Siting an Urban Ring LRT station in the Seaport (and the general challenges of using Track 61 for rapid transit to the Seaport)

Posted on by Riverside

The following is purely a fun exercise for a highly hypothetical scenario. I’m posting it more as an illustration of thought process, and not really in advocacy of the proposal itself. (There are many things I would prioritize above an Urban Ring LRT station in the Seaport!)

The scenario

Let’s assume a few things are true for this scenario:

  • The Piers Transitway (currently serving SL1, SL2, and SL3) is converted to light rail and connected to the larger light rail network via a subway running from Huntington Ave to Back Bay to South Station — we’ll call this the “Magenta Line”
    • “T-under-D” has been completed, meaning the subway now extends from World Trade Center station under the current grade crossing at D St to a portal near the current Silver Line Way station
  • Center-running bus lanes on Congress St in downtown and Summer Street in the Seaport have been built, and the T7 upgraded into a full bus rapid transit service, which we’ll call the “Navy Line”
  • SL1 service has been transferred to the Navy Line, to provide a one-seat ride connecting North Station, the Financial District, South Station, the Seaport, and the Airport
    • We’ll loosely assume that a lane in each direction of the Ted Williams Tunnel has been dedicated to mass transit use
  • An LRT iteration of the Urban Ring has been built on the southside of the network, connecting Longwood, Nubian, and the Seaport, approaching the Seaport via the Track 61/South Boston Haul Road ROW

In short, our starting point looks like this:

The satellite image doesn’t tell us the whole story, however. This is a highly three-dimensional space, where Summer St and World Trade Center Ave sit elevated above the rest of the street grid, and where a slew of highway tunnels sit under the surface.

World Trade Center Ave looking east, as seen from Summer St
World Trade Center Ave from above, looking north, with Haul Road below and to the right
World Trade Center Ave at “elevated street level” looking north, from nearly the same vantage point as above, but lower down
Track 61 and Haul Road passing underneath Summer St, from above World Trade Center Ave, looking west; the Boston Convention and Exhibition Center is visible at the far left
OpenStreetMap showing the tunnels below the surface

Where to place an Urban Ring LRT station?

“The gravel pile”

As visible in the photo above looking west along Summer St, there is a triangular plot of land bounded by Track 61, the embankment of Summer St, and (effectively) the elevated WTC Ave. (There’s actually an access road that cuts off the corner of the plot slightly east of WTC Ave.) That plot currently is occupied by a massive pile of gravel. (Last I checked, the plot is owned by MassPort, though I assume they would sell it off to a developer if/when they could.)

This is probably the most obvious place to plop down an LRT platform. It’s accessible from the current ROW with minimal modification and landtaking required; it provides good access to BCEC and easy transfer to the Navy Line services (including services to the airport); the Magenta Line subway station at World Trade Center is about 400′ away, which isn’t ideal but is certainly manageable, especially if one of the sidewalks can be covered for protection from the elements.

There are some downsides. The plot is a little small; if we leave the access road untouched, it’s just about 230′ along the long edge, which would be barely long enough for a double-set of the 114′ Type 10 “supertrains” that are expected on the Green Line in the next several years. So it’s likely the modifications at the east end, west end, or both would be needed to fit a center platform, two side tracks and a crossover. (Depending on how the Track 61 ROW is converted to double track LRT, some space might already be reclaimed from Haul Road at the western end, which might simplify the design somewhat.)

The other downside is that this location serves the Seaport, but only somewhat so. A lot of the Seaport is located on the other side of the “highway canyon” that Track 61 and Haul Road sit within, so Urban Ring passengers would need to go “up-and-over” for the last segment of their journey. The current World Trade Center station is much more centrally located.

The gravel pile is potentially an adequate location for a station, and would likely be the least expensive option. On the other hand, if we are going to go to the expense of building an LRT Urban Ring, there’s an argument that it should be built for maximum efficacy, rather than just minimal cost.

The underground parking lots

As can be seen in the photos, there are a number of parking lots at the grade level of Track 61, including one parking lot that directly abuts the southern wall of the current World Trade Center station; open that wall up, and you have a strong transfer to the Magenta Line.

The problem here is that you need to cut across Haul Road and the Mass Pike ramps in order to access the lot. And while that’s doable, it’s far from ideal. There actually already is a traffic light directly underneath WTC Ave on Haul Road, so in theory the disruption to traffic flow would not be new. On the other hand, you could only run trains so often if they need to disrupt traffic, probably capping headways at 5 minutes. Again, that is doable, but seems to trigger the same question as above — if we’re gonna build this thing, why not do it properly?

World Trade Center Ave

One thing that bothered me when thinking about mini-project was how to provide good transfers to both Summer St BRT and Transitway LRT. The distance between a stop in front of BCEC and the entrance to WTC station is roughly 650′, which is long for a transfer but not unheard of. (If I recall correctly, it’s roughly the distance of the transfer between Southbound Orange and Blue at State. Of course, State has the benefit of being entirely indoors, while BCEC <> WTC would have significant exposure to the elements, even if the sidewalk were covered.)

Having two Urban Ring stations — one for the Transitway and one for Summer St — seemed excessive. So then I got to thinking more about what the objectives are for stations/connections at each location.

Summer St

  • Boston Convention and Exhibition Center
  • Transfer to Summer St BRT toward downtown: South Station, Post Office Square, Haymarket, North Station
  • Transfer to Summer St BRT toward Logan
  • Transfer to Summer St BRT toward South Boston

Transitway (World Trade Center)

  • Seaport core, including Congress St and Seaport Boulevard
  • Transfer to Magenta Line westbound: western Seaport, South Station, Back Bay, Longwood
  • Transfer to Magenta Line eastbound: eastern Seaport

On paper, that looks like a lot of reasons for each, and maybe even more in favor of Summer St due to its connectivity, but when you look closer, some are less relevant:

Summer St

  • Boston Convention and Exhibition Center
  • Transfer to Summer St BRT toward downtown: South Station, Post Office Square, Haymarket, North Station
    • By definition, the Urban Ring will have multiple connections to downtown, so this is not a vital benefit
    • Also, Urban Ring riders will all but certainly be coming from locations that already have direct service to downtown — it’ll be a very uncommon journey to transfer in the Seaport
  • Transfer to Summer St BRT toward Logan
    • As you’ll see below, this benefit is in fact not going to be unique to Summer St
  • Transfer to Summer St BRT toward South Boston
    • I won’t put strikethrough on this one, but I will point out that most of the previous connection points along the Urban Ring corridor (e.g. Broadway, Mass Ave/BU Medical Center, Nubian) will hopefully have — and will be better served anyway — by direct bus service from South Boston
    • Again, the Seaport itself wouldn’t be a common transfer point

Transitway (World Trade Center)

  • Seaport core, including Congress St and Seaport Boulevard
  • Transfer to Magenta Line westbound: western Seaport, South Station, Back Bay, Longwood
    • As mentioned above, pretty much all of the Urban Ring stops between Nubian and the Seaport will have better ways to connect to South Station, Back Bay, and Longwood than via the Seaport
  • Transfer to Magenta Line eastbound: eastern Seaport

So, to me, the goal of an Urban Ring LRT station would be twofold: connect to the Seaport, and connect to Logan. A stop anchored by the Transitway station better serves the Seaport and, as you will shortly see, also serves Logan. So, insofar as we need to choose which connection to prioritize, we should focus on a Magenta Line connection at World Trade Center station.

Getting to Logan

In some alternate timeline, the Ted Williams Tunnel was built with a third tunnel to carry rapid transit rail service to Logan. This would’ve been so much better than today’s system, but alas.

In the scenario I’ve outlined here (and, in my opinion, in any vaguely realistic scenario), service to Logan is provided by BRT. Now, to be clear, BRT can be a lot better than what we have today. For one, a lane in each tunnel could be dedicated to transit and perhaps very-high-occupancy vehicles, with semi-permanent lane protection to ensure speedy and unencumbered journeys.

But our BRT services still need to get in to the tunnel, and the solution to that problem also solves the problem of Summer St vs the Transitway.

Today’s SL1 and SL3 services make a semi-unadvertised stop at street level on Congress St just outside of World Trade Center station; they do this immediately after exiting the off-ramp, which has the benefit of getting travelers from Logan to a stop in the Seaport quickly, without needing to double back from Silver Line Way.

This stop is marked on my diagram from the top of the post (though I am supposing that the simple sidewalk stop has been expanded into something more like a proper BRT platform):

As far as I can tell, absent a major rework of the Mass Pike tunnels, Logan-originating buses will exit from that off-ramp for the foreseeable future. Now, it is true that Logan buses could instead turn left and use Congress St bus lanes to head toward downtown. However, that would duplicate the lanes on Summer St which would still be needed for South Boston service (i.e. the T7), and would be more awkward to connect to South Station. And while Logan -> South Station is mildly more direct via Congress, the journey in the opposite direction is significantly worse, requiring a lengthy diversion down Haul Road in order to reach the on-ramp.

Funneling Downtown <> Logan service through Summer St maximizes frequencies on the shared trunk, minimizes redundant infrastructure, and maintains good Logan -> World Trade Center service. It is somewhat more roundabout, but connects to more places. (And if we are really worried about an express South Station <> Logan connection, using dedicated lanes in the Mass Pike tunnel running direct into the South Station Bus Terminal is probably a stronger solution anyway.)

So we’ve identified a way for our Logan -> South Station service to transfer at WTC station, but what about the other direction? Well, that’s where those parking garages can come in handy.

Running directly parallel to the Transitway is a small side street/alley that runs into the lower level of the parking garage, and which, I think exits on to Haul Road just underneath World Trade Center Ave. Visible in the second Streetview photo are two large metal doors: I am pretty sure that those lead directly into the lobby of the World Trade Center station — meaning that with some modifications, you could put a BRT platform near there, and have buses immediately proceed to the on-ramp.

This would then provide a strong transfer point to Logan-bound services at World Trade Center proper — benefitting Magenta Line riders, but also providing a crucial transfer point enabling an Urban Ring station at World Trade Center.

Placing an Urban Ring LRT station at World Trade Center

So, where to put a new LRT station at World Trade Center?

We can’t put it at grade level without disrupting all the highway ramps, or otherwise settling for a station at Summer St instead.

We can’t put it below grade level because of the highway tunnels.

What about above grade along the World Trade Center viaduct?

Building a short rising viaduct on the gravel pile’s plot and claiming some of World Trade Center Ave (more details on that below) to add a above-grade LRT platform, combined with building an at-grade BRT platform for Downtown -> Logan services by reclaiming some space under the parking garage and adding a BRT platform on Congress St for Logan -> Downtown service, enables all three services to be centralized in a single station for easy transfers between all three.

So how do you reach the World Trade Center Ave viaduct?

Some of this will depend on how Haul Road is reconfigured for double-track LRT, particularly in terms of the horizontal alignment (do you steal a lane, or eat into the gravel pile?), but I think there’s enough open space to feel comfortable that something could fit, even if we don’t work out the details right now.

One area we have less flexibility on is the vertical alignment: there’s approximately 310 feet of horizontal running space between the Summer St underpass and the edge of the World Trade Center Ave viaduct, and we have to fit our rising viaduct in there.

The WTC Ave viaduct is approximately 25 feet high; 25 feet rise over 310 feet run yields a grade of 4.61°, which is well within the comfort zone for LRT grades. Even a rise of 33 feet over that distance would still come in at our 6° threshold. Likewise, rising 25 feet at <6° is doable in as little as 240 feet. Therefore, even with the known limits, it should be possible to rise from the Summer St underpass to the World Trade Center Ave viaduct at a reasonable grade.

Fitting a terminal on the World Trade Center Ave viaduct

The main question facing us here is whether to maintain some level of automobile access through WTC Ave. I believe I’ve come across proposals to fully pedestrianize that street, which, honestly, based on my experience, seems pretty reasonable. Mostly it seems like the street is used to deliver goods to the World Trade Center proper.

If I needed to maintain some level of automobile access, I would use a staggered pair of side platforms to maintain LRT capacity and keep a shared bidirectional lane open for vehicles to pass through on a limited as-needed basis, placing signals/traffic lights at each entry to coordinate passes through the right-of-way.

Obviously, this arrangement is complicated and would create some disruption to the system, depending on the road traffic volume. This option would need to be considered carefully to assess the cost vs benefit.

The key thing to note is that there is horizontal space to fit all the necessary elements:

  • First 230′ platform (enough to accommodate a doubleset of the 114′ Type 10 supertrains)
  • 90′ to fit a crossover to provide passing access
  • Second 230′ platform
  • A 100′ radius curve from the rising viaduct on to WTC Ave
  • Reasonably short walking distance between platform and current headhouse to streamline transfers
  • Maintain pedestrian access to the elevated greenspace between Congress St and Seaport Blvd

The second option is more conventional and straightforward: pedestrianize the whole viaduct, and claim part of it for a GLX-style center-platform terminal station.

There are lots of potential variations on this design — adjusting the width, length, and placement of the platform, trying out different methods of pedestrian access — but they all more-or-less look like this.

Keen observers will note that none of these designs feature fare gates or paid-access vs unpaid-access areas. Numerous transit systems, both in the US and around the world, have demonstrated that it is possible to run ticketed transit systems that do not require metal barriers to enforce payment. Eliminating fare gates makes it possible to build transit access more directly into the fabric of a neighborhood. Both station designs, but particularly the staggered platforms alternative, see no clear demarcation of the “edge” of the station, but rather allow the space to be woven together into a seamless whole.

So how do you site an Urban Ring LRT station in the Seaport?

To me, it looks like this:

  • Add a BRT platform at World Trade Center station for Downtown -> Logan services (under the parking garage just south of the station)
  • Build a viaduct to connect Track 61 LRT to the WTC Ave viaduct
  • Add an LRT station at-grade on the elevated World Trade Center Ave viaduct

Should you put an Urban Ring LRT station in the Seaport?

One thing this exercise illustrates is that the Seaport is not very wide. This sounds obvious and trivial, but one result is that there isn’t really space nor need for a “crosstown” service. The Piers Transitway and Summer St already form strong “east-west” transit corridors (whose elevation difference reduces their overlapping walksheds slightly). But they’re still close enough that a perpendicular service between/across them wouldn’t make much sense (particularly since both originate at South Station and come very close to connecting again at World Trade Center).

So a Track 61 LRT service basically needs to choose a particular point along the “linear Seaport corridor” to terminate. That increases the pressure on that station to be located optimally to maximize access to jobs as well as to transfers. World Trade Center does reasonably well on that front, but both the eastern Seaport (e.g. Design Center) and western Seaport (e.g. Courthouse) would require transfers for short last-mile journeys. But this need to choose lies at the heart of why siting an Urban Ring LRT station in the Seaport is difficult in the first place.

A Track 61 LRT service will likely reach the Seaport in part by passing near Broadway station. Regardless of origin point beyond there, a service near Broadway likely could instead be aligned to pass through South Station instead — and then continue to Seaport along one of the east-west corridors. (For reasons I won’t get into here, a Piers Transitway LRT corridor would very likely have excess capacity to absorb Urban Ring LRT in addition to the Magenta Line LRT I’ve described here.)

Sending an “Urban Ring” LRT service down one of the east-west corridors would provide better access to the entire Seaport, and reduce/eliminate the need for transfers. Running LRT service via Track 61 may in fact be unnecessary.

This brings us to a key difference between an LRT Urban Ring and a BRT one: BRT can continue to Logan Airport and on to Chelsea much more easily than LRT. Rapid transit on the Track 61 ROW, with a transfer station roughly at World Trade Center, and continuing service to Logan is able to catch a much broader swath of journeys (in italics below), compared to service terminating in the Seaport:

  • Longwood <> Seaport
  • Nubian <> Seaport
  • Red Line transfer point TBD (e.g. Broadway) <> Seaport
  • Longwood <> Logan
  • Nubian <> Logan
  • Red Line transfer <> Logan
  • Longwood <> Chelsea
  • Nubian <> Chelsea
  • Red Line transfer <> Chelsea
  • Seaport <> Chelsea
  • Logan <> Chelsea

The concept of the Urban Ring was to provide circumferential service that bypasses downtown, for speedier journeys and reduced crowding in the core. A route that terminates at Seaport curtails possible destination pairs, and becomes less competitive against transferring downtown via the radial services (especially for long circumferential journeys).

Returning to the point about connecting at Broadway vs South Station: South Station is, to be clear, the bigger fish. Nubian <> South Station journeys surely outnumber Nubian <> Broadway journeys. Urban Ring concepts usually favor a transfer at Broadway or to the south — but can justify skipping South Station because they are providing speedier service to Logan and Chelsea. Track 61 LRT can’t do that.

So I think Urban Ring LRT service via Track 61 presents a weaker case than it first appears. Now, it bears mentioning that capital costs for a Track 61 LRT route would probably be less expensive than a journey via South Station. If given the choice between Track 61 LRT and nothing, I’ll be entirely in favor of the former.

Conclusion

Ultimately, this is a fun thought exercise. The scenario I’ve contrived here presupposes a lot of things, so its “real-world relevance” is somewhat limited. A few final thoughts:

  • The problems I’ve outlined here will impact any Track 61 proposal; Track 61 will always be on the wrong side of the Mass Pike between Summer and Congress Streets, so you’ll always need to figure out a way to bridge that gap
  • This conversation becomes radically different if an LRT connection between Seaport and Logan is built — although even then, Track 61 will still be on the wrong side relative to the Transitway
  • Urban Ring considerations aside, I’d suggest that a Navy Line service to Logan would significantly benefit from the “under-the-garage” platform I propose here, especially if the Transitway is converted to LRT and thus cut off from Logan
  • The Seaport is centered on two east-west corridors, and there’s an argument to make that almost all services, even circumferential ones, would do well to feed into or otherwise align with those

For all the reasons outlined here, and others, most of my crayon maps going forward will favor both LRT and BRT Urban Ring services that run via South Station, rather than Track 61/Haul Road. At most, I can see Haul Road being useful for express service to Logan that bypasses the Seaport — that, it could do quite well. But for serving the Seaport proper, I think it comes up short.

What I saw on the Green Line Extension

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As a holiday treat for myself, I went on a purely recreational trip to see the new Green Line Extension in action. Truth be told, I had a ball. Sitting in the so-called “railfan” seat, peeking out the front window as we sped along the Medford Branch, all of the politics and the delays could be momentarily forgotten, and I could enjoy the moment and say to myself, “Wow, this is so cool!”

The Green Line Extension has been in the works for decades. Its 2022 opening means that the one-seat ride between downtown and Union Square and other Somerville neighborhoods has returned after almost exactly 100 years. It is truly a delight to see it open at last. And make no mistake: any operational or aesthetic shortcomings notwithstanding, the bones of this extension are solid and will last for another 100 years if not longer. This is what long-term public investment looks like.

I took lots of notes and photos. Presented below are some of my observations. It is undisputable that many aspects of GLX remain in progress – there is still lots and lots of ongoing construction, for example. So I’m going to present my observations largely without commentary. I pay a lot of attention to details, and will share some of the particular details I noticed – I defer to more knowledgeable voices to assess the significance (or lack thereof) of those details.

All photos are dated Dec 26 2022. I’m writing this about a week after the fact, so it is possible that some of things have changed since my trip, though given the holidays, that seems unlikely.

Maps

Many maps across the system do not currently show GLX. By my observation, all four of the core Green Line transfer stations – Park St, Government Center, Haymarket, and North Station – have maps that omit the Green Line extension and physical signage that points to Lechmere.

The map at North Station is a typical example:

On closer inspection, someone (or multiple people, given the different ink colors) had tried to add in GLX by hand:

A similar situation on Park Street’s Red Line platform:

Park Street’s Green Line northbound island platform had a map and diagram with a sticker that read “Open Spring/Summer 2022”:

By contrast, all of the GLX stations had updated diagrams:

The GLX stations also all have those lovely neighborhood maps:

Quincy Adams (undergoing renovations) also shows GLX on its map in the paid lobby:

Maps within Green Line cars themselves were a mix, with some showing the extension and others omitting it. (Probably there was a pattern based on the older Type 7 vs newer Type 8 cars, but I wasn’t paying close enough attention to tell.)

Signage and wayfinding

“Stop Requested”

On my trip outbound on the Medford Branch, the operator came on the PA after departing Lechmere and said something to the effect of, “For stops on the Medford branch, please request your stop prior to arrival.” (She said something slightly clearer and more elaborate, but I don’t remember the exact phrasing.) The Stop Request sign lit up at every stop, and we made every stop.

On the inbound journey, there was no announcement. When we pulled in to Magoun Sq, no one had made the request, so the train came to a complete stop, but the doors did not open, and the train set off again. 

In full candor, the Stop Request system seems reasonable on the B, C, and E branches, where stations are about 750-1000 feet apart; it does not seem reasonable to me on the D and Medford Branches, where stations are much farther apart, and where the often 10-min wait between trains means that a missed stop costs you an additional 15 minutes of travel time (whether you walk or double back on a train). 

I should also note that there is no in-car signage on the Type 8’s to explain to riders how to request stops. (I didn’t specifically check while on a Type 7.) There also was no physical signage that I saw in any station about the presence of a Stop Request policy on the Medford Branch.

Next train indicators

I didn’t get a good photo, but the dot matrix indicators that display when the next train will come (e.g. “Heath St – 3 min”) often would just show something like “Trains every 8-13 minutes” on the inbound Medford Branch. As I understand it, this is because a specific countdown doesn’t begin until the incoming train departs Medford/Tufts. However, given that the travel time from Medford/Tufts is relatively short, that means that the countdown indicator will only ever give a few minutes’ worth of notice.

A similar problem happened on the northbound platform at Park Street: because the indicators only show the next two trains, there was a Union Square train only 3 minutes away, but it wasn’t visible on the board. 

Next departure track indicators

At Union Square (and also at Medford/Tufts, though I spent less time there), hanging above the platforms are a pair of arrows which are intended to light up to tell passengers which train will depart first. I didn’t get a great photo of them, but you can somewhat make them out in this one (under the overhang, bracketing a white lit panel):

I departed Union Square multiple times during my trip, but only tried to use the indicators during one of those departures; as it happened, the indicator pointed to the wrong track that time. 

Miscellaneous

A sign from the Aug-Sept 2022 Green Line shutdown sits tucked away next to the fare machines at Union Square:

The ramp appears to remain under construction at Union Square. As you can see, a small printed sign notes, “MBTA Ramp Closed, Please Use Elevator”. 

But in fact, the ramp was unblocked and appeared open, and had a series of small placards with details about the neighborhood (including some evidence of a Somerville-Saugus rivalry over the origins of marshmallow fluff):

Returning to that first photo of the ramp, you’ll notice that there is also an open staircase on the left, which appears to offer an alternative to both the ramp and the elevator. When you get to the top of the staircase, however, it is sealed off with a chain link fence; I did not see any signage to note this. 

Operations

Travel over the Lechmere Viaduct remains slow (at or under 10 mph). There was a small sign at the western end on the outbound track, saying “Resume speed.” Trains really fly on the Medford Branch, though – I would guess at least 35 mph. 

The automated announcement at Union Square said, “Doors will open on the left hand side,” but the train had already switched over to the other track – meaning the doors would open on the right. (Trains arrive and depart from both tracks at Union, meaning sometimes the doors will open on the left, and other times on the right.)

On one train as we entered Lechmere, the automated announcement said something to the effect of, “This is Union Square. The destination of this train is Heath St/VA Medical Center.” (Beyond announcing the wrong stop, this announcement also doesn’t make sense in that Union Sq trains now go to Riverside, not Heath.)

The inbound Medford train I was on got stuck at a “red over red” signal at East Somerville station (i.e. just before entering the junction with the Union Square branch). The driver eventually had to reset it manually. I overheard chatter on the radio later that suggested there was still an issue at that signal.

One of the outbound Union Sq trains I took needed to have its destination swapped to Medford; we pulled in to Lechmere, and the operators directed people out on to the platform where we waited for the next train (itself originally for Medford) to pull in. I wasn’t able to figure out why the first train needed to change destinations. 

On the Green Line Extension, the signals before switches say, “Stop, check for proper signal & switch”, and have little labels below – right arrow for Union, left arrow for Medford, that kind of thing; I’m sure that will make for a fun “Easter egg” for young railfans for many years to come.

On a very nerdy note: now that B and C trains both terminate at Government Center, the Park St Loop in theory does not see any regularly scheduled use (perhaps for the first time ever?). However, I saw at least one train getting short-turned on the so-called “fence track” at Park St, meaning that the loop continues to be used to short-turn trains to reduce bunching.

Infrastructure

The labels for platform level in the elevators at Union Square and Medford/Tufts used different styles for writing “Green Line” – the label at Union Square omits the space between the words.

Elevator buttons at Union Square
Elevator buttons at Medford/Tufts

One of the two elevators at Medford/Tufts was out of service.

Both doors to the Pedal & Park at Medford/Tufts had placards reading “Tap Charlie Card Here,” pointing to an empty space along the fence, where unconnected hookups were visible on the other side; I couldn’t see any place to tap a Charlie Card.

You get some really cool views of the Commuter Rail Maintenance Facility (Boston Engine Terminal) and the new Green Line maintenance facility from the Lechmere-to-Union viaduct:

I didn’t get good photos, but you also get a really cool view looking west from the Medford-to-Lechmere viaduct, from which you can see the Fitchburg Line commuter rail tracks, the Green Line’s flying junction tracks to/from Union, and the under construction Community Path that flies over everything:

And from the Lechmere-to-Medford viaduct, you get a cool view of the curved viaduct ducking under to go to Union, with the Green Line Maintenance Facility in the background.

While GLX stations are not unique in this regard, it is always cool to see level low-floor boarding, which I tried to capture in this quick shot:

The elevator at Lechmere has a lovely botanical pattern on its glass:

And finally, just before I was about to head home, I managed to snag a ride on one of the new Type 9 trains – I had tried earlier in the day to catch one but had barely missed it, and so had given up; as I was heading down to the Red Line platform at Park, I happened to turn around and see a Type 9 rolling in; so I delayed my departure in favor of a quick excursion up to North Station:

The Atlantic Ave El: A Story of Failed Aldgate Junctions

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Earlier this year, I described how Aldgate Junctions can be used to provide additional service along branchlines without impacting capacity on the core. But Aldgate Junctions have their limitations – a lesson that the Boston Elevated Railway (BERy) learned the hard way, 100 years ago.

The original Main Line El network

When what is now the Orange Line was first built, it was very different. In fact, the earliest iteration of the Orange Line did not use a single piece of track, tunnel, station, or right-of-way that the current Orange Line uses.

The Main Line El, as it was called, was opened in 1901, as a collection of three elevateds and one subway: the Charlestown El, the Washington St El, the Atlantic Ave El, and the Tremont St Subway. Yes – despite being opened less than 5 years before as a streetcar subway, the Tremont St Subway was semi-temporarily converted to third-rail and high-level platforms. (The four-track sections of the subway saw the inner tracks maintained for streetcars.)

The infrastructure of the Main Line El when it opened looked something like this:

Single els at the northern and southern ends were connected by a pair of downtown trunk lines, all linked together by a pair of Aldgate Junctions, the northern junction called “Tower C”, and the southern one called “Tower D”. This arrangement allowed all trains to run everywhere. For example, the following array of service patterns would have been readily achievable, with bidirectional service on each “line”:

(Note that I’m not sure a full service pattern like this ever existed; but, as you will see below, it looks like BERy experimented with many permutations, so this one may have been attempted at one point or another.)

Shifting into the Washington Street Tunnel and reshaping the network

The original network was short-lived. Within the decade, the Washington Street Tunnel opened:

As you can see, the Aldgate Junction at Tower C was preserved, but Tower D was modified into a simple flat junction. I argue that the asymmetric presence of the northern Aldgate Junction fatally undercut the Atlantic Ave El’s ability to contribute usefully to the network.

Mapping the lasting impact of the asymmetric Aldgate Junction

In the course of researching another project, I ended up doing a deep dive into BERy’s experiments with different service patterns on the Atlantic Ave El from 1919 to 1924. You can follow the evolution step-by-step below.

Ultimately, I would argue that the problem they were trying to tackle was a geometric one. Without an Aldgate Junction at Tower D, the Washington St El is hobbled by reverse-branching: every train you try to send from Dudley to Atlantic is one fewer train that you can send from Dudley to downtown; as it is today, downtown was the more popular destination and could hardly afford to lose service.

Trying out a shuttle service + deinterlining

This is why it is unsurprising that in 1919, BERy stopped running trains from Dudley to Atlantic via Beach St – all trains from Dudley would run through the Washington St Subway, as detailed in this newspaper announcement:

As you can see, BERy sought to increase frequencies on both the Tunnel and the El by isolating each other’s services; the Tunnel would be served by Forest Hills/Dudley-Sullivan trains, and the El would be served by North Station-South Station shuttles. (Not mentioned here is a dedicated track that existed at North Station, allowing Atlantic shuttles to reverse direction without blocking Tunnel traffic.) Drawing on the style of the Cambridge Seven Associates “spider map”, a diagram of the system at the time might have looked like this:

This was certainly a reasonable idea, and is a technique called “deinterlining” that remains in use to this day. (Every so often, you will see someone put forward a proposal to deinterline the NYC Subway, for example.) Two low-freq services offering dedicated one-seat-rides to multiple destinations are reshuffled into two high-freq services that provide higher frequencies to all stations, improve reliability, and maintain some OSRs, at the cost of turning other journeys into two-seaters. 

The push for deinterlining highlights a common pitfall of Aldgate Junctions: it entangles all three branches into a single shared timetable. Trains on one branch need to be coordinated with trains on both other branches. Even if your train is bypassing a branch, delays on that branch will still impact your journey through ripple effects. 

Pitfalls of a deinterlined main line + shuttle, and an attempt at remediation

But BERy’s own announcement reveals a fatal flaw in their plan: most of the major destinations on the Atlantic Ave El could be reached by other two-seat rides that were often more direct, especially for riders coming from the south. Why would anyone board a train at Dudley, ride it all the way to North Station, and then transfer to a shuttle and ride it the long way round to disembark at Atlantic (today’s Aquarium)? It would likely be significantly faster to transfer at State/Milk/Devonshire and ride an East Boston train one stop. (And probably would be just as fast to walk.) 

And from a convenience perspective: a two-seater is a two-seater, so Washington + East Boston is equally convenient as Washington + Atlantic. At that point, journey time becomes the deciding factor. 

Perhaps an Atlantic shuttle service could have been more successful if it had offered a southern transfer at Dover. Unfortunately, the Washington St El’s station construction style meant that significant capital investments would have been required to turn trains at Dover. 

As it stood, the 1919 Atlantic shuttle service was useful for three specific things:

  1. Shuttling passengers between South Station and North Station
    • Perhaps of limited use to long-distance travelers, but hardly a large market
  2. Serving Battery St
    • Located at the farthest edge of the North End, with half of its walkshed underwater
  3. Serving Rowes Wharf
    • Faced with declining ferry ridership and likewise only half of a walkshed

That is pretty wobbly, especially given the cost of maintaining the El and the diversion of rolling stock away from more heavily used segments.

(Of note – though I believe ultimately not of very much consequence to this particular topic – is the Great Molasses Flood, a disaster that occurred about two weeks after BERy’s announcement, and which put the Atlantic Ave El out of service for over two months.)

This experiment in pure deinterlining was short-lived. Just six months later (and less than three months into the service actually being consistently run following the flood), a Dudley-Atlantic-Sullivan service was reinstated:

Which would have looked like this (although I am unclear whether the Sullivan-Dudley service itself was weekends-only):

Implementing a “wraparound” service

The Dudley-South Station-Sullivan service – whether it was truly daily or only on weekends – only lasted another six months. In December of 1919, a fascinating “wraparound” service was instituted that essentially turned the Atlantic Ave El into a second northern branch of this predecessor to the Orange Line:

This change was briefly announced in November:

But it was given much more fanfare upon actually starting in December, including an interview with the Superintendent of Transportation. The article also includes details on the frequencies breakdown: 

The core stretch through the Washington Street Tunnel would see 24 trains per hour (tph) at peak. To the north, 8 of those trains would head to South Station, while the other 16 would go to Sullivan; in essence, BERy “paid” for a one-seat-ride to the Atlantic Ave El by diverting about one-third of Sullivan trains. 

(To the south, it should be noted, the 8 tph from South Station were short-turned at Dudley, again leaving the other 16 tph available to serve Forest Hills, though I’m not sure that they all did.)

Seasonal direct service

Sometime in the summer of 1920, a direct Dudley-South Station-Sullivan service was reinstated, to accommodate increased traffic from summer travelers. It’s unclear to me whether a North Station-South Station service remained during this time. 

Wraparound service + shuttle

However, by the end of September, the through-run was canceled, replaced by a return of the wraparound service – now only 6 tph – but now supplemented by a dedicated North Station-South Station shuttle, also running at 6 tph. 

Again, we see BERy reducing the frequency of one-seat rides, but adding additional short-turn service to raise frequencies on the El itself higher. 

Low-freq seasonal direct service + high-freq shuttle

Once more, however, after several months BERy shifted the service pattern again. In June 1921, BERy announced the return of Dudley-South Station-Sullivan direct service, citing the need to accommodate summer travelers.

Once again, the wraparound service was discontinued. This time around, however, BERy reduced the frequency of the direct service lower than I believe they ever had before: only 5 trains per hour. This was again supplemented by a much higher frequency on the North Station-South Station shuttle, which saw 10 tph during rush hour.

I think there’s actually a lot to be said for this arrangement. The lack of wraparound services means that trains aren’t doubling back on themselves; the frequency for Dudley-Atlantic-Sullivan services seems to match the present-but-low demand, sitting at the edge (but still within) the realm of “turn up and go”; and frequencies remain high on the core segments, meaning that riders who are impatient have the alternative of a two-seat journey between services with high frequencies (and therefore short transfer times).

Reverse branching from the south

It’s unclear to me whether BERy returned to a “Winter” service pattern after the 1921 Summer was over, and if so, which Winter service pattern they used.

However, it appears that the Summer pattern was again used in Summer 1922, before being replaced in September 1922 with yet another new service pattern:

This pattern essentially extended the North Station-South Station shuttle – a relatively constant fixture of all these variations – from South Station to Dudley. This again turned the Atlantic Ave El into a second northern branch of the Main Line El, but shifted the split point to the south to avoid the roundabout journeys of the wraparound pattern. This of course came at the classic cost of reverse branching: radial service from Dudley was rerouted away from the core, reducing the number of trains that could run between Dudley and Downtown.

As I understand it, this service pattern remained somewhat stable, though I am unsure how long it remained in place. By 1924, the predecessors to the Blue and Green Lines saw many of their surface routes truncated at Maverick and Lechmere respectively, which leaves us a map like this:

Writing on the wall

In 1926, the Report on improved transportation facilities in the Boston Metropolitan District noted that (p. 26):

At the present time the Atlantic Avenue Elevated loop is utilized principally as a rapid transit connection between the North and South Stations. It also affords a convenient means of reaching the several steamboat and ferry terminals along the waterfront. The total traffic served by this loop is not particularly important in a comparative sense. 

That same report called for the demolition of the Atlantic Ave El and replacing it with an “elevated roadway” (p. 41 and on) – essentially proposing the Central Artery, some 30 years before its time. 

By the late ‘30s, BERy listed the Atlantic Ave El as a separate route on its maps, running primarily between North and South Station. The El itself was demolished in 1938.

Other disadvantages faced by the Atlantic Ave El

To be clear, there were a number of factors that put the Atlantic Ave El at a disadvantage. For one, running along the shoreline meant that half of its walkshed was literally underwater. The route also avoided the densest parts of downtown Boston, in favor of serving the docks, which also reduced transfer opportunities to the Tremont Street streetcar services and to mainline railroads at North Station. 

(Transfer opportunities to the East Boston Tunnel were available at Atlantic, and to the Cambridge-Dorchester Subway at South Station; I would speculate, however, that passengers would likely prefer the shorter and fully-indoors transfers available on the Washington St Tunnel.)

Serving the docks was an understandable design decision at the time, but became more problematic as time went on. Tunnels under the harbor significantly reduced ferry ridership; for reference, the highly popular Boston, Revere Beach & Lynn Railroad ferried passengers across the harbor from their terminal at Jefferies Point to Rowes Wharf – surely a large source of passengers for the El.

Finally, it bears mentioning that Elevateds themselves quickly became unpopular. They were noisy, unsightly, and brought the noise of transportation up from street-level directly outside residents’ windows. Furthermore, since the Els were a rapid transit service that BERy used to express riders in from streetcar transfer hubs further out from downtown, stops were spaced distantly, and thus provided that much less advantage to residents who endured the costs of living nearby. 

What if?

Would things have been different if Tower D had been maintained as an Aldgate Junction? It’s hard to say. Maintaining a central “loop” service as I showed in my diagram above would still mean reducing the number of trains that could run directly between Dudley and downtown. 

On the other hand, a loop would have kept frequencies maximally high within the core Washington Street Tunnel, keeping capacity high for transfers from Cambridge, Dorchester, East Boston, and North Station. A loop service would also have created a one-seat ride from South Station to (what is now) Chinatown, State, and Haymarket.

Would it have been enough to save the Atlantic Ave El? In the end, I doubt it. The waterfront routing and probably the mere fact of being an elevated likely would have doomed it anyway. These were the early days of rapid transit – some ideas were simply best guesses, and so some ideas were inevitably wrong. 

Lessons for today

It’s clear that the asymmetric availability of an Aldgate Junction following the construction of the Washington Street Tunnel is the fundamental reason BERy kept changing the service patterns seemingly every six months circa 1920. BERy was trying, I would argue, to solve a physically impossible puzzle, experimenting with basically every possible permutation of service on the El, and failing to make any of them work.

The history of the Main Line El offers a lesson, not in the benefits of Aldgate Junctions, but in the perils of reverse branching and doubleback services. A key advantage of an Aldgate Junction is the “branch bypass” service: recall BART’s Orange Line that runs from Richmond to the East Bay without entering the core in San Francisco. 

In the case of the Atlantic Ave El, that advantage was negated: the experimental wraparound service was inefficient because it was a doubleback service that was roundabout and not fast enough to compete with more direct two-seat journeys. South Station-Sullivan service avoided the core of downtown, and consumed slots needed for the more valuable Sullivan-Dudley service. 

Why does it work in London?

London’s example may be a closer comparison than the BART’s: the eastern end of the Circle Line is also a doubleback service, as can be seen in the 2015 London Connections Map:

Why does it work in London where something similar failed in Boston? I think there are a few reasons:

  1. London has more people – a lot more people. Greater London had about 7.5 million residents in 1920, while Boston had a tenth of that (see pg. 143). Being physically smaller, 1920s Boston may actually have been roughly as dense as London, but you could probably fit (and I’m making a wild guess here) four or five “Bostons” into London’s areas of high density. 

    With that many people, the numbers game really begins to change. (This is a useful point to remember when comparing [Western] cities to London, New York, and to a certain extent Paris and Los Angeles – those cities are simply different due to their scale and are hard to use for comparisons.)
  1. The northern and southern legs of the Circle Line are a little bit further apart than the El and the Tunnel were, increasing incentive for passengers to ride around the bend even if it is slightly more roundabout.

  2. The Circle Line has fewer “crossing services” than Boston did: recall that riders could use the predecessors to the Red and Blue Lines to access most of the stops served by the El; London by contrast had more stops and fewer crossing services.

    If you were coming from Farringdon or points west and wanted to go to Monument, you could alight from the Circle Line at Moorgate and transfer to the Northern Line and go south one stop… but if you were going to Cannon Street or Mansion House, then you’d need to get back on a Circle or District Line train anyway, so why not stay on? The Central Line and Thameslink also presented options, but might have been undesirable for other reasons (see below).
  1. London’s large population becomes relevant when considering transfers; I don’t know what it was like in 1920, but today those segments of the Northern Line and Central Line are extremely crowded, while the Circle Line is noticeably less so. This again incentivizes riders to continue “round the bend”, to avoid an extremely crowded transfer.

Planning and crayoning

So what does all this mean from a transit planning and crayon mapmaking perspective? It means that an Aldgate Junction can solve some problems with branching, but it’s not a cure-all. 

It’s still vulnerable to the pitfalls of reverse-branching, diverting radial services away from the core. Every train from Dudley that went to South Station was a train taken away from the more valuable Dudley-Downtown route.

If the branches are close together, then an Aldgate Junction becomes less useful because it won’t be used for through-journeys from branch to branch – there will be other “crossing services” (including walking or biking) that are faster. Someone journeying from Scollay Square to what is now Aquarium was better off traveling via the East Boston Tunnel than going the long way around.

If the branches are long and are corridors unto themselves, then the Aldgate Junction can still be a useful way to increase frequencies within the corridor – but in that case it may be more efficient and reliable simply to short-turn supplementary services within the branchline itself, rather than deal with the logistics of a junction. 

In a Boston context, this would be relevant on the western branches of the Green Line: a “wraparound service” that jumps from the B to C Lines while avoiding Kenmore would be a poor alternative to the (idealized, well-running) 66, 65, or 47 buses. If frequencies need to increase within the Beacon or Commonwealth corridors, short-turning trains at Blandford St, St. Mary St or Kenmore would be more reliable and less complex than a junction. 

(This also holds true, in my opinion, at the western end of those branches, where there is a true set of Aldgate Junctions at Cleveland Circle and Chestnut Hill Ave.)

Summary

An Aldgate Junction is more useful when as many of the following are true:

  1. Branches are evenly distributed geographically
  2. The region is pluricentric, where key destinations are located across multiple branches
  3. The branches are long and form corridors unto themselves
  4. Direct “crossing services” (such as circumferential routes) are not available between the branches, or are too centralized resulting in three-seat-journeys (such as Farringdon-Moorgate-Monument-Cannon Street)

Even before the elimination of the Aldgate Junction at Tower D, the Atlantic Avenue El failed all of these. Following the relocation into the Washington Street Tunnel, BERy was hamstrung with no way to serve the El without incurring reverse-branching, doubleback services, or both. This is vividly illustrated by the rapid changes and experimentation with service patterns circa 1920. 

While the Atlantic Avenue El was demolished over sixty years ago, its history can still teach us lessons today.

Addendum: a GIF

Mapping the Orange & Green Line Closures

Posted on by Riverside

Over the past week, I’ve been iterating on modified versions of the T’s official subway map to illustrate the closures and shuttle services that begin tonight and will continue for 30 days. This map will likely continue to evolve, and I will continue to post the latest revision here. As always, please note that this is not an official map — always refer to the MBTA’s website and to the City of Boston’s website for up-to-date information.

Notes for transit and design nerds

This exercise started relatively simple: show the Orange Line and northern Green Line in some alternate manner to indicate the bustituted segments. This was relatively straightforward: I borrowed design language from the Arborway bustitution in the late ’80s, with a colored outline, white fill, and colored circles for the stops.

On the further advice of someone with better aesthetic sense than I, I shifted the white fill to a lightly colored fill, to better differentiate the lines, and avoid the perception of a total absence of service. The light fill seemed to strike a good balance between maintaining the line’s identity, showing the continued existence of service, and also indicating a significant difference in service.

But, as happens with many projects, I kept on thinking of, “Oh, just one more thing I can add!”

Which brings us to the current design, which pushes the original map’s information design to the limits. I wanted to show:

  • The bustituted segments
  • The un-bustituted segments
  • Text notes on significantly relocated shuttle stops
  • The one-way service at Haymarket
  • The early-morning/late-night shuttle to Chinatown and Tufts Medical
  • The bus routes the T suggests as alternatives to the Orange Line (39, 43, 92, 93, CT2)
  • The suggested walking transfers between Orange Line and Green Line stations

That is a lot of information to cram onto a diagram that was originally designed to be rather sparse. The current official subway map is an evolution of a design from the early 2000s that primarily showed the rapid transit routes, with commuter rail and ferries being shown secondarily, and limited-access highways being shown tertiarily. In the late 2000s, the key bus routes were added, and a subsequent redesign shifted some parts of the map around while maintaining the same visual language overall.

Evaluating my attempts

Was I successful? Ehn.

I was pleasantly surprised when an earlier version of this map gained a small amount of traction of Twitter, so it’s nice to know that at least some people found it useful. But at a certain point, I fear the level of detail hinders rather than helps. Part of the brilliance of Cambridge Seven Associates’ original “spider map” design was in its simplicity; even if you didn’t memorize the whole thing, the visual concept was highly memorable: four lines, crossing each other in a square and radiating out. That basic schema was easy to recognize and recall, and created a foundation to understand the rest of the system, even if it wasn’t put into one single map.

The eventual addition of commuter rail lines, key bus routes, and now all of the additional information I’ve added here is all very reasonable, especially when done incrementally. But I find myself questioning the ultimate usefulness of the diagram I’ve created. Is it really useful enough for journey-planning? Or is it too confusing to parse?

Simple maps and specific signage

Ultimately, I’ve come to believe that clear and specific wayfinding signage in and around stations is much more important than a detailed system diagram, both under ordinary and extraordinary circumstances such as the Orange Line Closure. (This despite my own love for detailed system diagrams.) In that way, perhaps my earlier, simpler diagrams were more effective.

Shuttle routes only

In this simplest version, the shuttle routes are shown and nothing else:

The advantage of this design is how minimally it alters the original, and (hopefully) how starkly clear the changes are: the most important thing is that the Orange Line and northern Green Line are different and need to be planned around. The question all of this hinges on: can the diagram provide enough information to adequately re-plan the journey? And that’s the part I don’t know.

Walking transfers

The second-simplest iteration added the walking transfers:

Including the walking transfers worked better than I expected. Quite frankly, I’d like to see these added to the official map (though hopefully a little more elegantly than I’ve done here). There are a lot of walking transfers that ought to be indicated on the system diagram, such as the ones I’ve included here, but also additionally:

  • State – Downtown Crossing
  • Government Center – Park
  • Riverway – Brookline Village
  • Reservoir – Cleveland Circle – Chestnut Hill Ave
  • Kenmore – Lansdowne

These transfers would not be suitable for everyone — and it should be noted that they are not free transfers under the current model — but if you are able-bodied and have a monthly pass that doesn’t charge per ride, these transfers are useful, speedy, and potentially can relieve congestion on key sections of the network.

Adding these transfers to the map is a good idea in general, but does it help in the case of the Orange Line & Green Line Closures? Again, I’m not quite sure. In most of these cases, I would guess that regular commuters are pretty familiar with the areas in question, and likely are well-aware that, for example, State and Gov’t Center are practically a stone’s throw apart. And if you aren’t a regular commuter… well, the pretty clear (and dire) direction from both the City and the T has been, “Please, stay away.”

Concluding Thoughts

Working on this diagram has been fun. It also has been nice to see positive response from numerous folks on Twitter. (Shout out to Jeremy Siegel at WGBH for sharing it with his followers!) And at least some of those positive responses have made comments to the effect of, “This is easier to understand than the materials the T has put out.” A few comments on Twitter aren’t necessarily a representative sample; however, the negative reaction to the T’s materials have been widespread and resounding — the Boston Globe going so far as to publish a parody of the official closure diagram.

That negative reaction suggests that there is room for improvement in how the T communicates these closures. I’d argue that the positive reaction to my diagram has been driven by its recognizable similarity to the “normal” map, combined with the clear-and-obvious differences that are blatant and draw attention to themselves.

With rumors swirling of partial shutdowns of the Green and Red Lines later this year, perhaps the T might consider adopting a similar strategy to what I’ve presented here.

The Green Line turns 100 today

Posted on by Riverside

“Wait”, you say, “that’s not right. The Green Line turned 100 in 1997, with the centennial of the Tremont Street Subway’s opening.”

True enough. But the Tremont Street Subway, for its first quarter-century of operation, looked quite different from the modern Green Line. It was only in the early 1920s that it began to resemble the system we know today, and it was only in 1922 – not 1897 – that the modern Green Line was born.  

An Underground Street

BERy (the Boston Elevated Railway Company, the MBTA’s primary private predecessor) saw the tunnel more like a substitute for the crowded street above than as a proper rapid transit subway. 

Streetcars funneled in from all over the city and distant suburbs, squeezing into the subway and crawling along at the speed of a modern bicycle. Contemporary accounts describe crowds surging down the platform at Park Street when the boarding location of the next trolley to such-and-such suburb was announced. The destination board at Park Street in 1899 resembles a departure board at a mainline station like South Station or Grand Central much more than that of a rapid transit station:

https://commons.wikimedia.org/wiki/File:Destination_board,_Park_Street_station,_1899.jpg

The streetcar subways draw a clear contrast with the services which BERy did consider rapid transit (the predecessors to today’s Red and Orange Lines). Beyond the difference in rolling stock (high-platform third rail vs low-platform wired), the rapid transit lines were also distinguished by their use of transfer stations.

A Tale of Two Transit Trips

Compare these two rider experiences:

  1. A commuter from Somerville boards a trolley at the intersection Highland Avenue and Willow Avenue. 
  2. The car trundles down Highland, stopping every couple of blocks to pick up passengers. 
  3. After 2.7 miles, the car reaches Lechmere Square…
  4. …where it departs from the street and enters the streetcar-only Lechmere Viaduct…
  5. …which snakes over the Charles and around the West End before…
  6. …diving into the subway just north of Haymarket.
  7. After another 1.5 miles, the commuter disembarks at Scollay Square

Vs.

  1. A commuter from Dorchester boards a trolley at the intersection of Blue Hill Avenue and Seaver Street (equidistant from downtown to the Highland/Willow intersection in Somerville). 
  2. They actually have a choice of trolleys – bound for Egleston, or bound for Dudley (now Nubian). 
  3. They travel by streetcar for 1 to 1.7 miles, stopping every couple of blocks to pick up passengers, 
  4. before arriving at their rapid transit station where they get a (free) transfer to the Elevated. 
  5. The Elevated speeds into downtown, with stops roughly every three-quarters of a mile. 
  6. The commuter disembarks at State Street.

The Somerville commuter takes a long slow ride from the suburb to the core, while the Dorchester commuter takes a short slow ride followed by a short fast ride, enabled by a transfer station.

A Tunnel Filled With Buses

For BERy, in those first 25 years, the Tremont Street and Boylston Street Subways were just ways of getting the huge volumes of streetcars off of the streets in downtown. In today’s terms, those tunnels were essentially filled with buses. This was useful transit service, to be sure, but it wasn’t rapid transit.

The same was true of the East Boston Tunnel. Extended from its Court Street terminus in 1916 to a portal on Cambridge Street (with a turnback loop at Bowdoin, still used today), the tunnel’s primary use was to bring East Boston trolleys under the Harbor into downtown. In fact, early in the planning of the East Boston Tunnel, one option that was considered was to have trolleys exit the tunnel from Maverick through a portal in the North End, and continue on street-level into downtown – similar to today’s Sumner & Callahan Tunnels. The primary use of the tunnel was to get trolleys (or “buses”, if you will) under the harbor – not to create rapid transit service. 

In the early 1920s, that all began to change. 

Conversion to Rapid Transit

Birth of the Blue Line

The 1924 conversion of the East Boston Tunnel to rapid transit is well-known and offers a clear example of how a streetcar tunnel can be transformed into a rapid transit subway. The vestigial surface route on Cambridge St was converted to bus, and the half-dozen streetcar routes to the east were cut back to terminate at a new transfer station at Maverick. Thereafter the local streetcar services fed into a dedicated rapid transit service, mirroring similar designs at Dudley, Harvard, Sullivan, and others. 

This, I would argue, marked the birth of the modern Blue Line; while it is true that today’s State (f.k.a. Devonshire) and Aquarium (Atlantic) stations opened some 20 years prior, it was only with the 1924 conversion that the service became anything like its modern form.

(There’s also an argument to be made that the true birth of the modern Blue Line actually occurred a bit further to the east, during the early and highly successful years of the Boston, Revere Beach & Lynn Railroad, which was essentially running Indigo Line-style service 100 years before its time.)

As a matter of comparison: mainline rail service with today’s rapid transit stop spacing had been running along both the Highland Branch and what is now the Southwest Corridor for 70 years and 100 years respectively before their conversion to rapid transit; but I don’t think we would say that either the modern Green Line or Orange Line were born circa 1888. We would consider those to be predecessor services, and I would argue that we should view the streetcars in the East Boston Tunnel as a similar predecessor service (albeit of a different character).

Birth of the Green Line

Less well-noticed – but I would argue equally important – was the 1922 construction of the transfer station at Lechmere. Like at Maverick, local streetcars were now short-turned at a rapid transit station where passengers transferred to service that was dedicated to bringing riders downtown at high speed.

In fact, in those early years, BERy ran a dedicated service to Lechmere for this purpose; a “shuttle” service ran from Lechmere to the Pleasant Street Portal for the first six months, which was rerouted to Kenmore in early 1923. Note the similarity to the East Boston Tunnel’s rapid transit service – “shuttle” services whose sole purpose is to run between downtown and a transfer station. More information in a contemporary newspaper account here.

Over the following ten years, BERy experimented with extending Lechmere service on to the Commonwealth and Beacon branches, which eventually both through-ran to Lechmere until the early 1960s. With their dedicated medians, the Commonwealth and Beacon branches were indeed the most “rapid-transit”-like of the various services feeding into the Central Subway at the time. They still intermingled with “local bus”-like services to Watertown, Huntington, Egleston, Dudley, City Point, and Sullivan, but the clear intent was to create a “rapid transit” service, as much as possible. 

The efforts to replicate the success of the “rapid transit transfer station” model were originally envisioned to go even further. As discussed previously in my Blue Line series, plans were made for another transfer station in Allston, which is why Kenmore station – not constructed until 1933 – was built with a loop for the Beacon line; the hope had been to convert Kenmore into a transfer station for a Beacon streetcar and a Commonwealth rapid transit line, Maverick-style. You can see a 1926 proposal for such a network here:

https://upload.wikimedia.org/wikipedia/commons/thumb/0/0f/Map_of_1926_proposal_for_Boston_rapid_transit_lines.png/1024px-Map_of_1926_proposal_for_Boston_rapid_transit_lines.png
https://en.wikipedia.org/wiki/Green_Line_E_branch#/media/File:Map_of_1926_proposal_for_Boston_rapid_transit_lines.png

The construction of the Lechmere transfer station marked the turning point from BERy treating the Tremont Street Subway as a collection of independent streetcar routes into BERy treating the Subway like a trunk line with multiple feeder branches – in short, the modern Green Line.

Death of the Streetcar Network

Following the cutback of the Lechmere services, the once-expansive network of streetcar routes running into the subways (a subject for a later post) started a rapid winnowing in which the same story played out again and again: a transfer station was constructed and the streetcar route was cut back to the transfer; once a route no longer needed to travel into the subway, bustitution almost always quickly followed.

This is one place I want to draw our modern attention to. I’d always thought of bustitution as a phenomenon of the latter 20th century, driven by the post-war embrace of the automobile. In fact, the vast majority of bustitutions happened between 1922 and 1941. If anything, the pace rapidly slowed following the war, and it is in fact remarkable that Arborway survived all the way to 1985. 

  • 1922: Lechmere Network cut back once transfer station opens
  • 1924: East Boston Network cut back once Maverick opens
  • 1925: the Ipswich Street Lines (the predecessors to today’s 55, 60, and 65) were truncated at Massachusetts (now Hynes) station
  • 1932: the routes along what is now Route 9 to Chestnut Hill were bustituted and redirected to Kenmore’s surface station
  • 1935: last year that foreign streetcars from the North Shore ran into the subway, halted by the loss of the bridge over the Mystic River
  • 1938: the local streetcar running below the El along Washington St between Dudley and the subway was substituted with a bus (described here)
  • 1941: the Huntington Avenue Subway opened, and streetcars stopped using the Public Garden Incline. 

At this point, the winnowing slowed significantly, and the system had largely transformed into the modern Green Line we know today, with a few extra branches (to Egleston, City Point, and Charlestown) hanging around.

  • Late ‘40s: the two Charlestown branches are eliminated, just barely outliving BERy itself
  • 1953: the City Point branch is eliminated by the MTA
  • 1956: the Egleston branch is cut back to Lenox Street
  • 1959: the Riverside Line is converted to light rail, expanding the MTA’s reach to Route 128
  • 1961: the Lenox Street branch (formerly running to Egleston) is cut back to the Pleasant Street Portal, and briefly runs as a shuttle service between Boylston and Pleasant Street
  • 1962: the shuttle to Pleasant Street is canceled, and the Pleasant Street Portal – once an anchor of the streetcar subway – falls into disuse
  • 1965: through a consulting engagement with Cambridge Seven Associates, the newly incorporated MBTA assigns colors to its rapid transit lines for the first time – the literal origin of the term “Green Line” (as well as the birth of the iconic spider map)
  • 1969: the “A Line” – having survived long enough to actually be called “the Green Line” – is eliminated

And in this context, we now see that Arborway’s survival all the way to 1985 almost seems improbable by comparison – the last in a 60-year effort to remove all streetcars from the subway.

The cruel irony is that this effort – originally intended to speed up service and improve reliability in the subway – contributed to an overall degradation of transit access in the region over the following century. Once streetcar routes were taken out of the subway, they were very easy to replace with buses, and once they were replaced with buses, it was very easy to quietly degrade or eliminate service. 

Conclusion: 100 years of the Green Line

In writing this, I read a lot of old reports written about Boston transit in the early twentieth century. One thing that struck me is that the reports written in the 1920s have much more in common – in terms of priorities and perspectives – with today’s approaches than they do with the reports written by their predecessors a mere 30 years beforehand. 

By the 1920s, recognition had set in that the streetcar subways could and should be converted into rapid transit, using the same transfer hub model that had been successfully deployed at Sullivan, Dudley and Harvard. 

(Interestingly enough, it had also become clear by this point that those elevated railways – built barely twenty years earlier – were awful and needed to be replaced as soon as possible; both the Southwest Corridor alignment and the current Haymarket North alignment to Sullivan were explicitly described in the 1926 report.)

The 1922 opening of the new Lechmere transfer station marked this pivot point, after which every single capital exercise carried out on the streetcar network was done with the aim of turning the subway service into a rapid transit service – or getting it as close as possible. 

This continues to this day! The Green Line Extension project is undeniably a rapid transit project, and not just a resurrection of the former Lechmere streetcar network, and the same will be true if the Green Line is ever extended to Needham. Moreover, it seems all but certain that a Green Line extension to Nubian Square would need to find ways to make itself as “rapid transit”-like as possible – or else face a century of institutional inertia to overcome. 

The notion of a “Green Line” with branches feeding into a trunk – as opposed to an urban streetcar network whose density called for a tunnel in key locations – arose in the early 1920s. Today’s Green Line is much more closely related to the LRT subway service of the 1920s than of the 1900s, in structure, operation, and public branding. It arises out of 1920s ideas about hub-and-feeder networks, which had previously been applied on other routes, and were then brought to the streetcar networks following their success. The creation of the rapid transit line that would become the Green Line occurred not in 1897, but in 1922.

And so, that is why, this summer I’m celebrating the Green Line’s (true) 100th birthday.

Acknowledgements 

I am indebted to a host of transit historians, who have produced reams of carefully researched accounts detailing the stories of Boston’s transit system over the decades; most of them did so as volunteers, producing labors of love that exemplify the root of the term “amateur”. I want to specifically mention the names of Ron Newman, Bradley Clarke, O.R. Cummings, Frank Cheney, and Anthony Sammarco, as well as the volunteers who maintain the Wikipedia pages on Boston’s transit network. 

Introducing the Aldgate Junction, a countermeasure to reduced frequencies on branches

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In a previous post, I described the mathematical inevitability of decreased frequencies on branchlines. But I also alluded to a particular feature that certain systems have that allows them to bypass this particular pitfall. And that brings us to today’s post. 

Introduction

Let’s take a simple trunk-and-branch system, which sees 10 tph six-min headways on the core and 5 tph twelve-min headways on the branches:

If those branches are out in the suburbs, those lower frequencies may be justifiable. But what if your system needs to branch within the core?

Introducing the Aldgate Junction:

(“Aldgate Junction” is a term I’ve coined to describe this kind of infrastructure and service pattern; there are other related terms, but I think the way I’ll be using this term is a useful addition to our vocabulary.)

An Aldgate Junction enables a second layer of service to travel in one branch and out the other, without touching the core and (usually) without a reverse move. Sometimes this can be created via a relatively minor infrastructure change, such as adding a third leg to create a wye junction, but sometimes a more significant capital project is required.

The original Aldgate Junction

The original “Aldgate Junction” is actually a trio of junctions and is located at the interchange of the District, Metropolitan, Circle, and Hammersmith & City lines:

(Image modified from Wikipedia’s version.)

You can see the layout of the three junctions and their names on this track map from CartoMetro.

The Aldgate Junction concept is deployed here to create a triangle of one-seat rides:

  • Liverpool St to Aldgate East via the H&C
  • Aldgate East to Tower Hill via the District Line
  • Tower Hill to Liverpool St via the Circle Line

Modifying my original diagram above to match the colors allows us to see how the Tube’s topology maps on to the generic model I’m discussing here:

The downside of the original Aldgate Junction in London is that it’s a level crossing, meaning trains block each other as they pass through, which creates a bottleneck. Some Aldgate Junctions utilize flying interchanges to avoid conflicts and increase capacity. 

Real-life examples of Aldgate Junctions

There are lots of ways to deploy an Aldgate Junction. It can provide distributed service to decongest central transfer points, or can be used to serve pluricentric regions with multiple “downtowns”. It can also be used to increase frequencies within the corridors of the branchlines, which is valuable for local trips as well as cases where the branch line is unusually long. 

Northern California

In my previous post, I mentioned that BART – a rather exceptional rapid transit system due to its enormous reach and mid-low frequencies on each branchline – uses an Aldgate Junction to increase frequencies on its East Bay services. 

BART’s Orange Line (also still sometimes called the verbose “Richmond-Berryessa/North San Jose Line”) plays the role of the “branch-to-branch bypass service”. For example: without the Orange Line, stations like Fremont would only see 15-min headways; Fremont is about 30 miles away from San Francisco, so 15-min headways might be appropriate for that service. But Fremont is only 15 miles away from San Jose, and there is a steady level of density running all the way up the East Bay – there are plenty of local journeys that sit squarely in “Rapid Transit Land”, and 15-min headways underserve that. 

Providing the Orange Line overlay raises headways to less than 10 minutes throughout the entire West Bay, without impacting capacity in the San Francisco core. Key to this is the Oakland Wye, a three-way flying junction to enable crossovers without interference. This is an example where an Aldgate Junction required significant infrastructure.

There are numerous other systems that use variants of the Aldgate Junction. 

The VTA Light Rail in San Jose has one between Tasman, Champion, and Baypointe. This is a simple flat junction in a four-way intersection.

Southern California

Moving further down the coast, we find that Los Angeles’ Metrolink commuter rail system actually has two Aldgate Junctions, of different varieties.

First, we see that the Orange County, Inland Empire-Orange County, and 91/Perris Valley lines form an Aldgate Junction in Anaheim. This creates a three-way link between Orange County, LA County, and Riverside County.  

But there is a second, more abstract Aldgate Junction, formed by the Orange County, Inland Empire-Orange County, and San Bernardino Line, between LA County, San Bernardino County, and Orange County. 

In both cases, these exemplify the use of Aldgate Junctions to serve distributed areas of density. Los Angeles is the core of the system, but Riverside and San Bernardino are major urban centers in their own right, and the use of the Aldgate Junction model creates two sub-networks based in Riverside and in San Bernardino. 

The “Riverside Network”
The “San Bernardino Network”

These examples, it should be noted, are cases where an Aldgate Junction is not functioning to increase frequencies; Metrolink’s frequencies are pretty poor, usually only about 1 tph at peak, and little-midday service. In this case the focus is on providing one-seat-rides across a decentralized network, enabling transit journeys to non-Los Angeles destinations that otherwise simply wouldn’t be possible.

New York & New Jersey

Finally, the reigning North American monarch of the Aldgate Junction is New York City.

The New York City Subway has several physical Aldgate Junctions, a notably consistent design feature of the old IND network, highlighted below. 

https://en.wikipedia.org/wiki/File:NYC_subway-4D.svg

The PATH system is built around a pair of Aldgate Junctions (forming an impressive set of underground flying junctions):

https://commons.wikimedia.org/wiki/File:PATH_daytime.png

And the Hudson-Bergen Light Rail offers a classic example of a simple Aldgate Junction near Hoboken Terminal:

https://commons.wikimedia.org/wiki/File:HBLR_diagram.svg

PATH and the HBLR offer an additional lesson about the operational realities of Aldgate Junctions; the maps above represent the daytime versions of those networks. On weekends (and in PATH’s case, at night), the Aldgate Junctions functionally disappear.

Modified from https://commons.wikimedia.org/wiki/File:PATH_afterhours.png

Modified from https://commons.wikimedia.org/wiki/File:HBLR_diagram.svg

All journeys remain possible, but some require transfers. 

PATH offloads its HOB-WTC journeys into a two-seat journey with transfer at Grove St; meanwhile, its two routes out of 33rd St are combined into one, with a reverse-move at Hoboken as part of the revenue service pattern. (Functionally, Hoboken is serving as a transfer point in the same way as Grove St; PATH just does the transfer for the passengers by throwing the switches rather than swapping out trains.) 

HBLR maintains weekend service to Hoboken, but riders from the north must transfer at Pavonia/Newport and backtrack. 

Summary

Aldgate Junctions provide a way to distribute service across a larger area and offer a way to increase service levels on branches without being constrained by trunk line capacity. Their physical form and implementation vary widely, from level wye junctions to complicated flying interchanges to dispersed routes spread across miles. These forms defer in capacity, reliability, and cost.

Despite these differences, Aldgate Junctions are united by consistent contributions to network topologies, and are a valuable tool when designing (and future-proofing) complex systems. 

Mapping the Bus Network Redesign: Somerville’s Buses, Present and Proposed

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Some of the earliest public feedback on the MBTA’s Bus Network Redesign (mapped in a previous post) came from residents of Somerville (and, to a lesser extent, Cambridge) who were – almost unanimously – unhappy with the proposals. 

City Councilor Judy Pineda Neufeld gave lengthy feedback, praising the increases in frequency, and raising serious concerns for riders from West Somerville (in particular Clarendon Hill), and those trying to reach Union Square and the nearby Market Basket. Others seconded the concern about lack of access to Market Basket, as well as poor connectivity to GLX, some suggested that GLX was mistakenly being viewed as a substitute for current bus service, and numerous people noted that a lot of ideas in the Redesign were pretty good, but that Somerville appeared to draw the proverbial short straw.

Based on my anecdotal observation on social media platforms, it appears that initial reaction from other communities has been more muted; this may change in the coming weeks with the further feedback sessions the T has planned. But still, I thought it was interesting that there was such an immediate and resounding response by comparison from Somerville.

I don’t envy the Redesigners their task with the Northwest Quadrant um, Sextant (?). Uniquely, they had to design for a system that doesn’t exist yet: GLX will be a seismic shift in transit access for Somerville, and while some of its effects are predictable, some are not. That’s a pretty big wildcard to toss into the mix.

The early signs suggest the Redesigners missed the mark, at least from the perspective of the community. I wanted to dig in to this and – of course – wanted to make a map to add to the conversation. I believe that I have been able to piece together a visualization that offers context and some explanation for this initial pushback; based on these, I have also generated some modest suggestions for revisions to the Redesign.

Further details are below, but the core of my suggestion is “swapping” the proposed T39 and proposed 90; this provides an increase in service to most riders, but is a more conservative change that does not disrupt existing travel patterns. This extension can be “paid for” by a dramatic shortening of the proposed 87 to its core service area, a reroute of the 90 to a shorter well-established corridor, and the use of a lower-freq crosstown route and a shuttle service to address connectivity gaps to Sullivan and Assembly.

The Map

I had two goals with this map: visualize frequency, and visualize potential destinations. I chose these goals because they reflected themes I saw in the initial feedback: frustration at multiple transfers (meaning, need for direct access to a larger number of destinations), and loss of service, particularly for lower-income residents (which I believe in some cases was a result of the Redesign’s shift away from “mid-low frequency” routes – think 45-min peak headways, that kind of thing).

Line color denotes reachable destinations. This system isn’t perfect, but I think captured some key dynamics. 

  • Dark red lines reach Red Line stations 
  • Dark orange lines reach Sullivan Square specifically, and light orange lines serve other Orange Line stations 
  • Dark green lines reach Lechmere 
  • Dark blue lines serve Longwood Medical Area

Some lines see multiple colors, meaning a rider might board a bus for multiple destinations; a good example of this is the 87 & 88 north of Davis, where a rider might board destined for Davis or for Lechmere.

Line width indicates frequency. 

  • The thinnest lines have peak headways more than 30 minutes
    • such as the 85 or 90
  • The next size up, forming a large swath of the network, denotes headways between 15 and 30 minutes at peak, including 
    • the 95 along Mystic Ave, 
    • the 87 along Somerville Ave,
    • the 83 along Somerville Ave and Beacon St
  • Thick lines indicate peak headways of 15 minutes or better – matching the target for the Redesign’s frequent network, and including major corridors along
    • Broadway 
    • Highland Ave, 
    • College Ave, 
    • Washington St
  • The thickest lines – matching the width of the rapid transit lines – see peak headways of less than 10 minutes, including 
    • the 77, 
    • the cumulative 87 & 88 between Davis and Clarendon Hill, 
    • the 101 & 89 on Broadway running into Sullivan

Here’s a version of the current system only showing routes that see 15-min peak headways or better.

Here we see six distinct corridors emerge:

  • Medford Square (and Malden) – Main St – Broadway – Sullivan
  • Powder House Square – Broadway – Sullivan
  • College Ave – Powder House Square – Davis
  • Clarendon Hill – Davis – Highland Ave – Lechmere
  • Arlington Center – Porter – Harvard
  • Sullivan – Union – Harvard – Allston/Brighton and Reservoir

I then created a map using the same design language to visualize the Redesign proposal.

(I recommend opening the “before” and “after” images in separate tabs, and then switching between them to hone in on the differences. I tried creating a GIF, but was unsatisfied with the results.)

Impact to current high-freq corridors

Let’s first review the impact to the current high-freq corridors:

  • Medford Square (and Malden) – Main St – Broadway – Sullivan
    • Largely intact
    • Goes near but does not provide transfer to GLX at Ball Sq
    • Extended beyond Sullivan to provide a (long) one-seat ride to Lechmere and Kendall
  • Powder House Square – Broadway – Sullivan
    • Eliminated
    • Moreover, this route is actually composed of a pair of branching routes:
      • a mid-freq route to Davis
      • a low-freq route direct to Clarendon Hill
    • Davis and Clarendon Hill lose direct service to Ball Sq GLX and Broadway
    • Davis and Clarendon Hill maintain roundabout access to Sullivan via Mystic Ave, an increase of 0.5 miles
  • College Ave – Powder House Square – Davis
    • Intact and strengthened
    • Newly anchored at north by Medford/Tufts GLX and extension to Medford Sq
    • Worth noting that the twice-hourly one-seat ride beyond Davis to Porter and Harvard is eliminated
  • Clarendon Hill – Davis – Highland Ave – Lechmere
    • Significantly reduced, and partially eliminated
    • Clarendon Hill – Davis gets a pair of the Redesign’s “30-min-or-better” routes, which could approximate 15-min headways, but still does not meet the current service’s average sub-10-min frequencies
    • Highland Ave drops into the Redesign’s “30-min-or-better” routes, but does not connect to Lechmere, or to Union GLX, or even to Gilman GLX (though it comes close), but instead is rerouted over toward Sullivan… which it doesn’t actually reach, instead ultimately diverting to Assembly
  • Arlington Center – Porter – Harvard
    • Intact
  • Sullivan – Union – Harvard – Allston/Brighton and Reservoir
    • Partially eliminated
    • Sullivan – Harvard is maintained, and combined with through-service to Everett
    • However, ridership from one side of Harvard to the other is actually surprisingly high, so this elimination is not trivial

Of the six current high-frequency corridors, three are maintained and three are significantly impacted. This does seem counterintuitive – as far as I can tell, all other existing high-freq corridors across the system were maintained in the Redesign, and most were significantly strengthened. I suspect the difference in Somerville was the future presence of the Green Line Extension.

Green Line integration (or lack thereof)

One of my biggest surprises on seeing the Redesign was how little integration there was to the GLX stations. Ball Sq and Gilman Sq will both see bus routes pass less than a quarter mile from the station without offering door-to-door service.

In addition, despite the arrival of the Green Line, Union Square now sees less connectivity than it did before, including the loss of one-seat rides from Clarendon Hill, Davis, and Kendall. As Councilor Pineda Neufeld pointed out, this also reduces access to the Market Basket in Union Square, as well as the Star Markets on Beacon St and Elm St.

I would argue that the Redesign treats the Green Line Extension more like one of its high-freq bus routes than like a rapid transit line – as if the GLX has said, “Don’t worry buses, I’ve got this stretch”, and thus bus routes are routed away from it. That is not done with any other rapid transit lines, and with good reason: rapid transit access is concentrated in discrete areas around stations; a key role of surface transit is to provide access to a station from beyond its walkshed. Unlike rapid transit, the close stop spacing of bus routes provides continuous access along the entire route, which GLX lacks.

To be clear, for over a century now, Somerville’s surface transit routes have had to play double-duty, providing both feeder service into rapid transit stations, as well as longer-distance service to support journeys that would in other areas be covered by rapid transit. GLX relieves them of the second burden, but not the first. 

To wit: the entire Red Line from Davis to Kendall is doubled by surface transit routes in the Redesign. It is true that GLX’s stop spacing is closer than the Red Line’s, but it’s still well-above typical surface transit stop spacing. The Green Line is not a wholesale replacement of local buses.

Highland Ave vs Elm St & Somerville Ave

In the current system, Highland Ave sees mostly 15-min-or-better service at peak on the 88, from Davis to Lechmere. Pre-pandemic, the average AM Peak frequency was 10 minutes. (The 90 layers on about one trip per hour to Sullivan.)

By contrast, in the current system, Elm St & Somerville Ave sees lower frequencies on the 87, wobbling between 15 and 20 minute headways. Pre-pandemic, the average AM Peak frequency was 22 minutes. 

(A short stretch of half-a-mile between Elm and Park Sts on the northern half of Somerville Ave sees additional 20 minute headways on the 83, running to Central Square via Inman. North of Elm, the 87 and 83 split, though remain only a couple of blocks apart for some distance. Pre-pandemic, the 83’s average AM Peak frequency was also 22 minutes.)

In the Redesign, Highland Ave drops into the 30-min-or-better category, and loses direct connections both to the Green Line and to Sullivan. (I should again note that 30-min-or-better routes still may see high-frequency peak service, which perhaps is the vision in this case.)

By contrast, Somerville Ave sees a significant increase: the 83 holds its place, while the 87 between Union and Porter is supercharged as the T39, receiving 15-min-or-better service. Somerville Ave also maintains a direct connection to the Green Line – only one of two radial routes in Somerville that do so, the other being the T96.

In essence, the Redesign swaps the frequency tiers of Highland Ave and Elm St & Somerville Ave. As mentioned above, Highland Ave is one of the current high-freq corridors, so its exclusion is puzzling.

I am guessing that the Redesigners saw the extent to which the 88 parallels GLX, and believed the Green Line would be an adequate replacement. As discussed above, however, surface transit and rapid transit are different beasts; the 88 is being relieved of its rapid transit duties by GLX, but not its surface transit duties. 

Moreover, while it’s true that the 88 parallels GLX for a lengthy distance, they diverge significantly after Magoun Sq GLX – GLX aims for Tufts and beyond, while the 88 aims for Davis and beyond. And as numerous people noted in the reactions I linked earlier, the 88’s corridor north of Davis is not meaningfully accessible from GLX.

Increasing frequency on Somerville Ave is not necessarily a bad thing – the problem is how the increase is achieved. The current Somerville Ave corridor runs uninterrupted from Clarendon Hill to Davis to Porter to Union to Lechmere. The Redesign shears off the southern half of this corridor, and joins it to an extended T39, running Porter to Union to Central and beyond to Longwood. That is a bold proposal, but it also dismantles a one-seat ride that has been in place for over a century.

This reflects a larger challenge introduced by treating the Clarendon Hill buses as feeders to Davis Sq, rather than acknowledging their actual roles as parallel spines threading the city together, radiating not from the Red Line at Davis, but from the Green Line at Lechmere. 

Lack of through-running from Clarendon Hill

It is worth highlighting that the current system offers one-seat rides at least half-hourly from Clarendon Hill to: 

  • Davis station
  • Porter station
  • Harvard station
  • Powder House Square
  • Ball Square 
  • Magoun Square
  • Broadway
  • Sullivan station
  • Highland Ave
  • Somerville Ave
  • Union Square
  • Lechmere station

The Redesign reduces that list significantly:

  • Davis station
  • Powder House Square
  • Highland Ave
  • Sullivan station (bus journey lengthened by half mile)
  • Southernmost Broadway, near Sullivan
  • Ball Square (via a 6 minute walk)
  • Porter station
  • Harvard station
  • Magoun Square
  • Most of Broadway
  • Somerville Ave
  • Union Square
  • Lechmere station

For over 100 years, Somerville has been tied together by crosstown routes on Highland and Somerville. The Redesign makes the unfortunate decision to reduce the Highland corridor, and breaks what is currently a single seat journey across the city from Clarendon Hill to Union Square via Somerville Ave into an almost-certainly three-seat journey. 

On paper, it may look like Clarendon Hill is all set with feeding into a hub at Davis; in reality, the Redesign takes numerous journeys that have been single-seat rides for – again I emphasize – over 100 years and makes them essentially impossible. 

Suggested revisions

I want to emphasize that I don’t mean to besmirch the Redesigners or their efforts: this was a herculean task that is impossible to get perfect. Tradeoffs had to be made, and balances struck. I can understand how they arrived at their current proposal, and I also can understand why community members are deeply unhappy. 

In this post, I have attempted to detail the nuances of the current system, to illustrate some of the features that I believe underlie many of the criticisms that have been levied against the Redesign. I want to conclude by offering some modest suggestions for revising the Redesign to address the concerns that have been raised. 

The Map

Methodology and fudge functors

While I am not sure that it has been stated explicitly, I believe the Redesign was undertaken with a “net zero” assumption – meaning the Redesigners assumed they could only work with the existing buses the system has today, and not increase the number of buses overall. As such, I am going to frame my suggested modifications through a reallocation lens: if I propose lengthening one route, I will attempt to balance it out by shortening another.

There are also fudge factors at play here that may provide some wiggle room on these proposals. First, infrastructure upgrades such as bus lanes and transit priority signaling may enable faster service and thereby reduce the number of buses needed to maintain frequencies. Second, it may be possible to spread minor frequency decreases across multiple routes to free up enough buses to add a new route – enabling the creation of a new high-freq route without eliminating routes elsewhere. 

These fudge factors cut both ways, of course – in some cases, they may make things harder, not easier. So while I’ve done my best to consider these suggestions as carefully as I can, I am of course limited to the data available to me; these suggestions should thus be considered preliminary. 

Generating a surplus

I suggest the following revisions to free up buses to accommodate additional changes below. For those interested, I’ve laid out the justifications for these changes in much greater detail in the appendix to this post.

  1. Shorten the proposed 87 along Mystic Ave to terminate at Harvard St
  2. Shorten and reroute the proposed 90 to Union Sq GLX via Somerville Ave (essentially recreating the current 87’s route)
  3. Institute an MBTA-run frequent shuttle service between Sullivan and the Assembly Row development, potentially leveraging public-private partnerships

Cumulatively, these modifications generate a surplus of 6.18 “route-miles” at 30-min-or-better frequencies.

Utilizing the surplus

  1. Reroute and extend the proposed T39, running Union Sq – Highland Ave – Davis – Clarendon Hill
  2. Revise the proposed network to include a 60-min-or-better route running Davis – Highland Ave – Sullivan, along the corridor of the current 90 (it may be possible to run this service at 30-min-or-better)

Suggested revisions in review

The core of my suggestion is “swapping” the proposed T39 and proposed 90; this provides an increase in service to most riders, but is a more conservative change that does not disrupt existing travel patterns. This extension can be “paid for” by a dramatic shortening of the proposed 87 to its core service area, a reroute of the 90 to a shorter well-established corridor, and the use of a lower-freq crosstown route and a shuttle service to address connectivity gaps to Sullivan and Assembly.

As detailed in my appendix, I believe these changes 

  • are achievable with a net-zero impact on the overall Redesign
  • maintain better continuity with established travel patterns and community corridors
  • still provide specific and general enhancements of service to most riders, per the Redesign’s objectives and philosophy

I commend the Redesign team on their thorough and innovative work. I hope they will carefully review these suggestions and the further feedback provided by the community, and consider adopting these changes into a revised version of the Bus Network Redesign.

Thank you, as always, for taking the time to read!

Mapping the MBTA Bus Network Redesign

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Background and Goals

For the vanishingly few of you who both read this blog and are unfamiliar with the MBTA’s Bus Network Redesign, you can check out the details of the proposal on the MBTA’s website.

In short, the MBTA is undertaking its first bottom-up redesign of its surface transport network in 100 years. The vast majority of the T’s bus routes once were streetcar routes; some routes have seen minor-to-moderate modifications in the ensuing decades, but the need to avoid disrupting the live system — which governs the day-to-day realities of thousands of people — has always capped how much could be done. As part of the long-running Better Bus Project, the T has conducted a deep dive review of its existing routes, including their ridership and reliability (see the Better Bus Profiles) and user research speaking directly to riders and community members.

Years in the making, the T this month released a proposed redesign of its bus network — details at the first link. This is a massive undertaking, and I give the redesigners credit for very clearly trying to avoid the “We’ve Always Done It Like This” Syndrome that plagues so much of American transit planning (especially in Boston).

Like any proposal, it has its imperfections and flaws. From my perspective, there are some things I like, and some things I don’t. There already has been some initial community feedback, and the T has a docket of public meetings (in-person and virtual) through mid-summer to collect feedback.

For the most part, I don’t intend to use my platform here to evaluate the merit of these proposals. The most important voices here are those of community members — their opinions should be listened to first, and given paramount consideration. Instead, my hope is to add to the discourse by providing additional ways to view and conceptualize the redesigned network — mainly through maps.

(There is one area of the proposal which received swift and strong public criticism. I have a post, and a pair of maps, in the works on that, where I will attempt to illustrate the flaws that have been pointed out by the community, and hopefully offer some modest suggestions to improve the proposal to address those problems. Stay tuned.)

In this post, I will share a map I have created to illustrate the Redesign’s “15-minute network”: a series of bus routes that are proposed to have 15-min-or-better headways all day from 5am to 1am, seven days a week. I’ll use the map to highlight some system-level features of the Redesign, and hopefully provide a framework for deeper discussion.

The Previous 15-Minute Network

Some of you may recall that I made a similar map of then-current all-day high-frequency MBTA bus services in the past. My methodology was a little different, so it isn’t a perfect comparison, but it is a useful starting point for our discussion today.

I also wrote on ArchBoston a detailed analysis of this network and its notable features, as well as a follow-up analysis specifically on the Dorchester network. There were a few things that stood out in that analysis:

  • Very few circumferential or crosstown corridors — almost everything was radial
  • Morning peak frequencies were often higher than afternoon
  • The bus network “breathes”
    • An entire subnetwork of high frequency services turns on and off during the peak, providing much more comprehensive service during rush hour, but a signficantly sparser network during middays, evenings, and weekends
  • The entire northern quadrant of the network — everything between the Red Line and the Blue Line — was bereft of (intentional) high-frequency all-day routes, with the sole exceptions of the 111 in Chelsea and the 116/117 in Chelsea/Revere
  • Some communities, like Everett, don’t show up on the “Gold Network” (high freq all day) because they are instead served by a more diffuse number of routes spread across the city, operating at lower frequencies
  • The absence of the North Shore network — meaning the absence of consistent high frequency service — was conspicuous
  • The Dorchester network is one-of-a-kind, with features that don’t exist elsewhere
    • The network itself is actually three networks superimposed: a “10-minute all-day network”, a “15-min peak, low off-peak network”, and a “low frequency network” — most routes fall very cleanly into one of these three buckets

(Interestingly, that last point about the Dorchester network[s] seemed to be on the mind of the Redesigners as well — they’ve also adopted three primary tiers: a “≤15-minute all-day network,” a mid-frequency network that I’m guessing will be “15-min peak, 30-min off-peak”, and a low frequency network that, like Dorchester’s, would mostly see hourly services. I won’t really go into much detail here, but in my previous analysis, I did note consistent characteristics about each of the Dorchester subnetworks, and I see many of those ideas applied systemwide in the Redesign.)

I mention all of these points because I believe the Redesign recognized these features as well, and explicitly designed their proposal to address them.

The Proposed 15-Minute Network

The Redesign calls for a series of 26 high-frequency routes that would see 15-min-or-better headways all day everyday from 5am to 1am. This proposal goes much farther than the system I described above — in particular with its commitment to late night and weekend service. Vanishingly few corridors see any level of service approaching this currently. Routes on this network would be indicated by a “T” prepended to their route number: the T39, the T111, and so on.

I’ve spent a while digging through the weeds of the Redesign, and have concluded that the 15-Minute Network is composed of three kinds of routes.

Radial Routes

These are straightforward: routes that radiate out from the core, and which feed into major transfer stations such as Harvard or Forest Hills. On my map below, I have used a dark blue for these routes. Most of these routes are unsurprising, and many of them are identified on my Gold Network map above.

Circumferential Routes

These routes offer crosstown service that goes around the core rather than pointing toward it. Some of these routes behave like radial routes as they approach their terminals; for example, the southern half of the T96 essentially radiates out from Porter and Davis. So these routes still will be used by commuters going to downtown — but they also will enable journeys between multiple subway lines that can avoid going all the way to downtown. The T1 is a classic example, connecting Roxbury and Cambridge without requiring riders to change at Downtown Crossing.

Two exceptions

There are two proposed routes that do not fit cleanly into the categories above or below: the T109 and T101, both running through Sullivan. North of Sullivan, they behave clearly like radial routes, to Medford/Malden, and to Everett/Malden. South of Sullivan, they do something that bus routes historically have not done: continue on from one transfer station to another.

Traditionally, these would be considered circumferential routes. However, I have mapped them as radial routes — I believe the Redesigners are trying to reconceptualize these corridors as radiating instead from Harvard and from Kendall, passing through Sullivan somewhat incidentally. I of course have no insight into their actual thought process, but I think it reflects general trends they’ve shown in favor of longer routes that pass through multiple quadrants of the system.

Longwood Medical Area Routes

This is by far the most seismic shift in the redesigned network. For the first time, Boston is proposing a transit network that acknowledges that Longwood is a major employment center, a third “downtown” equivalent to Back Bay and the Financial District. See for yourself:

Full size version here; data source: https://onthemap.ces.census.gov/

The current network requies riders to rely on employee shuttles, bus transfers at Ruggles, funneling riders on to the E Line and D Line, and lengthy walks. Despite being less than 2 miles away, commuters to LMA from Warren St currently have a single one-seat option — the 19, which only runs to Longwood during peak hours, mostly falls short of 15-minute headways during peak, stops running altogether by mid-evening, and offers no weekend service. (And it was no better pre-pandemic either.)

The Redesign proposes extending most major routes from Ruggles beyond to Longwood; it extends Cambridge crosstown service beyond Central to Inman, Union, and Porter; it adds a new crosstown route to the Seaport; and it increases frequencies on most existing routes.

When I did my analysis in 2020, the Kenmore-Longwood-Ruggles corridor saw 15 buses per hour during the morning peak, 4 per hour midday, and 6 per hour during the evening peak. The Redesign notes that exact routings through LMA are tentative pending further study, but by my count, the number of buses per hour between Longwood and Ruggles, Nubian, or Roxbury Crossing is proposed to increase to at least 20 buses per hour, all day.

I’ve colored the Longwood routes in dark red on the map. Some also act as radial routes to other hubs, and some do double duty as circumferential services in the larger network. But Longwood is undeniably the center of gravity, and makes for a distinct subnetwork, worthy of its own identification.

The Map

A few additional notes here:

  • This map is my creation, based on materials published by the MBTA; it is not an official map and any errors are mine. I recommend using my map as a jumping off point before reviewing the official materials.
  • Each route is marked separately and indicates a minimum of 15-minute headways (4 buses per hour) all day every day — I am sure that many if not most routes will see significantly higher headways during peak
  • Certain major bus stops are indicated, largely for the purpose of indicating transfer points to rapid transit; stop placement is not exact
  • Some potential “transfers” would require some walking, indicated by a dotted black line
  • The proposed Blue-Red Connector and potential Silver Line Extensions are indicated with dotted lines
  • Some corridors see high-frequency service provided by layered mid-frequency services; these are mostly indicated by the line splitting and ending with arrows
  • This map is not precise and is meant to illustrate the overall network, not detail individual routes
  • Some routes have been simplified to reduce clutter. For example, the T39, T9, T70, and most of the routes in Chelsea, all have significant stretches where the route splits on to parallel one-way streets; most of these, I have simplified by drawing the route through the block in between the streets

And voilà:

Massive full-size version here

If the full-size version is killing your browser, here is a link to a slightly lower-resolution version.

Here’s a detail view on Back Bay and Longwood, probably the most visually cluttered part of the map:

Conclusion

I do want to emphasize again that I am not trying to evaluate the quality or suitability of the Better Bus Project’s Bus Network Redesign proposals. There are elements of the proposal that I believe are transformative in that they are shifting the conversation in ways that are vitally necessary: centering Longwood, insisting on consistent high frequencies all day everyday, and creating wholesale new corridors that do not descend from the old streetcar network.

But the devil is always in the details, and there are many details to sort through in this proposal. My hope is that my overview and map can make it easier for you to wrap your head around this sprawling project, and from there, dive into the details, well-armed with a larger context.

Inevitabilities in Life: Death, taxes, and decreased frequencies on branches

Posted on by Riverside

In my previous post about branches, I briefly discussed the rapid decrease in frequencies as you add more branches to a trunk line. You might remember a diagram that I showed: 

A service level diagram, where the trunk has 15 tph, and then 5 tph branch off, leaving only 10 tph to the next station, after which the line splits into two branches of 5 tph each

In this diagram, the trunkline sees high-frequency headways of 4 minutes (which is better than many subway lines in North America). With such a high frequency, it’s easy to think that there’d be enough trains to serve a bunch of branches.

But as you can see, four-minute headways equals 15 trains per hour. If you have three branches, that means each branch gets 5 trains per hour – which yields 12 minute headways. If these branches are out in suburbia, 12 minute headways might be appropriate, but you’ve nearly reached the limit. If you were to add a fourth branch, each branch would see less than 4 trains per hour, at 16 minute headways, at which point you really no longer have a claim to “frequent service”.

In my last post, I recommended, as a rule of thumb, no more than two branches per line. However, I didn’t explain why. It comes down to a combination of typical throughput capacities, and mathematical inevitabilities. 

Divvying up trains-per-hour among multiple branches

Consider this chart:

I will post a text version of this table in the next few days!

On the left side, we have a list of potential trunkline capacities, measured in trains per hour. These indicate how many trains in each direction you can squeeze through your trunkline in an hour. (Don’t worry about converting these numbers to headways – I’ll get to that below.) 

For some perspective (most numbers pre-covid): 

  • BART ran 16 tph through its core section from Daly City to West Oakland
  • CTA ran between 12 and 20 tph on its Red and Blue Lines during peak
  • WMATA ran 15 tph on its Red Line during peak
  • MBTA ran 15 tph on its Red Line during peak
  • London Underground’s throughputs vary widely from line to line, with some lines seeing over 30 trains per hour, following major infrastructure and modernization improvements
  • Beijing’s subway runs between 30 and 35 tph on several of its routes
  • Shanghai’s subway runs between 15 and 32 tph on most of its inner routes

All of which is to say, the top few rows represent trunkline capacities that require major investment in transportation infrastructure.

To the right of those trunkline capacities are the number of trains available to each branch, depending on how many branches you have. So, for example, in the first row, a 40 tph trunk will provide 20 tph to two branches, 13.3 tph to three branches, 10 tph to four branches, and so on. 

As mentioned before: you’ll notice that, as you move from left to right across the chart, the numbers in each row drop dramatically. In fact, the decrease is literally exponential; you can describe the chart above using

y = n-x

where n is the capacity of your trunkline in tph, x is the number of branches, and y is the resulting tph per branch.

Decreasing frequencies due to decreasing tph

It’s helpful to start this discussion using tph as a measure, because it’s easier to recognize the patterns in the numbers’ decrease. However, once we convert those tph into headways, it’ll become that much clearer why branching quickly leads to decreased frequencies.

I will post a text version of this table in the next few days!

I’ve added some (opinionated) color-coding, meant to suggest the various “levels” of service these different frequencies provide. 

  • The bright green (every 5 minutes or better) represent the highest tier of frequent service an agency might provide. “Turn up and go.”
  • The pale green (every 5-10 minutes) are still comfortably in the realm of rapid transit, but are probably better suited to off-peak periods and lower-ridership networks. “Turn up and wait a couple minutes and go.”
  • The yellow (every 10-15 minutes) are the lowest tier of what could be considered “turn-up-and-go,” describing services where riders don’t need to check a schedule when planning journeys. Call this tier “turn up and wait.”
    • This tier should be approached cautiously, with careful attention paid to the specific corridor where these frequencies would be deployed.
    • (Sadly, consideration should also be given to reliability; if a bus is scheduled to show up every 13 minutes, but one run gets dropped, suddenly you have folks waiting nearly a half-hour for their bus.)
  • The subsequent tiers are rarely going to be considered “frequent service”; some could be “salvaged” by adhering to a strict clockfacing schedule: a route that reliably comes exactly :13 minutes and :43 minutes past the hour can be a useful service that isn’t “turn-up-and-go”, but doesn’t require consulting a schedule either. These tiers break down something like this:
    • Orange = “plan when to leave, but journey whenever”
    • Light grey = “plan when to journey”
    • Dark grey = “schedule around the schedule” 

As you can see, our frequencies drop through the tiers I’ve described above quite quickly. Once you hit the yellow tier, you’re teetering on the edge of frequent service, and once you hit the orange and beyond, you’re definitely over the edge.

Different regions will have different definitions of “high frequency”. For example, it’s pretty rare to wait more than 4 minutes for a tube train in central London; a six-minute headway would be considered sub-par. In Boston, we are sadly accustomed to six-minute peak headways on the Orange Line, while Baltimore’s subway sees peak service every 8 minutes. 

It’s worth highlighting that reaching 90-second headways at 40 tph on heavy rail is exceptionally difficult. If you have multiple tracks in the same direction, it becomes more manageable, but a standard two-track subway is nearly impossible to operate at 40 tph per direction, outside of the world’s most advanced subway systems. And notice – even the top examples I listed above, such as Beijing or London, you’re still looking at that second row as your baseline, at around 30 tph. Even in those systems, having more than two branches knocks each branch down into a lower “tier”, meaning it’s not suitable to do within the urban core. 

If your crayon map requires shoveling 40 trains per hour through a trunk line, then probably it’s worth trying to plan a second trunk line!

Gaming out examples, and dealing with the unideal real world

Many of the North American systems I mentioned above see 4 minute headways on their core. If we go to that row, we can see two branches gives us 8 min (good so far), three branches gives us 12 min (borderline), and four branches gives us 16 min (no good). 

Some North American systems see base headways of 7 or 8 minutes. In that case, our drop-off happens even faster: 2 branches becomes borderline, and 3 branches sinks us with headways longer than 20 minutes.

On the London and Chinese systems mentioned above, trunklines see headways around 2 minutes or better. In theory, those trunklines could accommodate five or six branches; but if you drop the core headways by just one minute, suddenly you can only accommodate three or four branches at similar frequencies. 

And that “in theory” caveat is what’s really going to get us. Even if you can squeeze 30 tph through your trunkline to get 2-min headways, if you are feeding that trunk from five branches, that’s five times as many opportunities for delays and disruptions. We just saw above that the difference between a 2-min headway and a 3-min headway is worth two whole branches of throughput. That’s a very thin margin for error – meaning that you need reliability to be extremely high, or else the whole system will unravel, with cascading delays across your network.

The exceptions that prove the rule: North American legacy subway-streetcar networks

There are only two networks that I’m aware of which see sub-10 minute headways on four or more branches, feeding into a trunkline handling 40 tph: the MBTA’s Green Line and SEPTA’s Subway-Surface Lines.

This level of throughput is achieved (see caveat below) mostly because they are light rail lines rather than heavy rail. This means shorter trains which can start and stop faster, and therefore can be run closer together (albeit at lower speeds). The MBTA allows multiple Green Line trainsets to enter certain stations simultaneously, and SEPTA actually treats a couple of its subway stations as “request stops”, with trolleys rolling through non-stop if no one signals to board or alight. 

(I haven’t done the math on this, but it would be worth someone calculating the actual capacity of those two systems compared to heavy rail equivalents. It is true that the TPH levels are higher, but since the trains are shorter, I don’t know that you actually end up carrying more passengers.)

The reality, sadly, is that both of these networks are infamous for their reliability issues. (Full disclosure: I’m much more familiar with the MBTA than SEPTA, but I believe most of the T’s problems also exist in Philadelphia.) Delays are common, both on the branches and then resultantly in the core, potentially resulting in less than forty actual trains per hour through the core. 

Having four or five branches is somewhat workable on these two systems due to their unusual characteristics. Replicating that success elsewhere would likely require replicating those characteristics as well.

The other exceptions that prove the rule: hybrid rapid transit/commuter rail systems

BART’s core trunkline from Daly City to West Oakland feeds out into four eastern branches (Richmond, Antioch, Dublin/Pleasanton, Berryessa/North San Jose). Likewise, the London Undergroud’s Metropolitan Line runs to four termini in the northwestern suburbs (Uxbridge, Amersham, Chesham, Watford). 

Both networks accomplish this by running service to distant suburbs that is more like high-frequency commuter rail than traditional rapid transit service. Each branch on the BART runs every fifteen minutes, which isn’t super unreasonable given that most of those branches travel over thirty miles from downtown San Francisco. (BART is also a pluricentric network, which makes the ridership patterns a bit different than, for example, Chicago’s.)

The Met in London is a bit more complicated, but the concept is similar. Similar to New York, and unlike BART, the Metropolitan is quad-tracked for certain stretches, and therefore runs both local services and express services. During peak hours: 

  • Uxbridge sees 10 tph (6 min) spread across local and express services, with 4 of those trains short-turning at Baker Street
  • Amersham sees 4 tph (15 min), half of which are express
  • Chesham sees 2 tph (30 min)
  • Watford sees 8 tph (7.5 min), again with some short-turns and some expresses

A couple of further notes for context:

  • Almost all of the Uxbridge branch is also served by Piccadilly trains – 12 tph at peak – providing a robust 22 tph, which creates headways under 3 minutes
  • The Amersham and Chesham services run together until Chalfont & Latimer, before splitting off and going one stop each to their terminus, meaning most of the branch in fact sees 6 tph; these services are also supplemented by at least 2 tph that run on Chiltern Railways to Amersham and beyond. 
  • Chesham is also the most distant Underground station – 25 miles from Charing Cross in central London, and technically outside of Greater London – well into territory where 30-minute headways might be reasonable
  • The town of Watford is served by three other stations; the largest of these is Watford Junction, which is less than a mile from the Met station, and sees 4 Overground trains and about 5 London Northwestern Railways trains toward London per hour

So, the Met has a few mitigating factors:

  • Its branches are supplemented by additional services
  • Despite four possible termini, really it just has three branches, one of which splits at the very end
  • The only stations that see 15-minute-or-worse headways are distant suburbs, over 20 miles from the core of London

Like SEPTA and the MBTA, both BART and the Metropolitan also have unusual characteristics that enable them to get away with breaking my “two branches max” rule of thumb.

However, both BART and the Met also have an additional special feature that allow them to have their cake and eat it too… to be continued in the next post! 

Branches are not your friend

Posted on by Riverside

When I was a kid, I wanted to send branches everywhere. As a child, it was an easy concept to understand — I knew that branches came (like the Braintree or Riverside branches) and that branches went away (like Watertown), and if the Green Line used to have five branches, maybe it could have six or seven or eight! And if the Green Line could have eight branches, why couldn’t the Orange Line? 

Obviously, with age has come a modicum of learned wisdom; I stopped drawing branches everywhere and tried to focus on only sending branches where train service actually was reasonable. But there is more to the picture than that.

It is tempting to think of subway branches like roads. If you build a new road, it means that more places are connected. Providence and Hartford don’t have an interstate highway between them — you have to drive north or south first and pick up Route 84 or Route 95, and then head west. It takes longer than it would if there were an interstate directly between them, which is why you will occasionally hear proposals for one. Two disconnected places ought to have a connection between them.

Rail systems don’t work like that most of the time (and actually road systems don’t either, but that’s a different topic).

There actually is a surprising amount to discuss on this topic! Here are some rules of thumb:

Two branches max

For most systems, do not give an HRT/subway line more than 2 branches. A light rail line, or a commuter/regional rail line, can probably take more, but keep in mind the other rules of thumb below.

One evening I decided to jump down this rabbit hole and did a cursory review of pretty much every heavy rail subway system in the world. Almost none had HRT lines with more than 2 branches. Most of the exceptions were themselves exceptional systems, such as BART or London’s Metropolitan Line, both “subway” lines that act more like commuter rail lines, especially along their branches.

Consider frequencies

Branches have low frequencies, trunks have high frequencies. Trunks should only branch once they are far enough from the urban core that lower frequencies will be feasible. 

Most transit systems in North America have a “full-build reach” (even if hypothetical) of a 10 mile radius from the center. Your trunk shouldn’t branch too close to downtown; every city will be different, but in general you’ll want your trunk to branch no closer than 5 miles to the core. If you need to branch closer to the core, you should try to create a second trunk line.  

Remember that branching frequencies are almost always a hard-and-fast math problem: If your trunk line can take x trains per hour max, then two branches can each feed no more than 50% of x. That is often going to be enough to knock a “high-frequency” trunk service into a “mid-frequency tier” on the branches. As such, it’s worth conceptualizing a branch as something less than a “full” rapid transit line.

In the diagram below, note how the trunk line has a high frequency of 4 minute headways via 15 trains per hour, but that splitting it up into three branches very quickly drops frequencies to 12 minutes on each branch.

A service level diagram, where the trunk has 15 tph, and then 5 tph branch off, leaving only 10 tph to the next station, after which the line splits into two branches of 5 tph each

Read more about decreasing branch frequencies in my follow-up post on this topic.

Trunk line capacity should be your starting point

It’s important to recognize that branches are (usually) a game of subtraction, not addition. Your trunk line provides the pool of trains that you can send out to multiple branches. Unless you know that the trunk line is under capacity, you should assume that they are shoveling through as many trains as they possibly can, and can’t add more. So you need to think about redirecting the existing pool of trains, which is why this is a game of subtraction and not addition. 

Note that I said this is usually a subtraction game – some newer/younger rail systems will not be at capacity. When that is the case, a branch proposal can work in your favor: proposing the addition of a second mid-capacity branch can combine with the existing mid-capacity service to create high-capacity service in the core (where presumably demand will be higher). Especially in newer metro systems, there may not be sufficient existing demand to justify the capital expenses of expanding the fleet to increase service in the core; adding a branch can broaden your revenue base, and enable the purchase of enough vehicles to run high-frequencies in the core. (Sometimes – these calculations are always going to be complicated.)

Look for short-turn services (and over-capacity extremities)

Transit agencies are incentivized not to run extraneous services. The further out from the core, the lower the demand for service (very much theoretically, but I digress). One solution agencies use are short-turn services, in which some fraction of vehicles do not run the full-length of the route. Sometimes this is done to reduce the number of near-empty vehicles running on the outskirts of the line, and sometimes this is done in order to increase the reliability of service on the inner sections of the line (and sometimes both). Short-turns are very common on bus routes, but do have their role in rail transit as well. 

If your trunkline has an existing short-turn service, that is a very strong jumping-off point for a new branch: it points to a confirmed high-frequency trunk/mid-frequency branch demand model, and it doesn’t require additional capacity to be freed up in your trunk, since you aren’t trying to funnel a greater number of trains per hour through. (You will still need to expand your fleet size to maintain existing frequencies, although you may be able to adjust frequencies elsewhere in the network to account for the longer trips your short-turn services will now be taking on the branch).

A simple route diagram, from "Downtown" to "Beltway" to "Suburbia", before and after. Before, half of all trains terminate at Beltway (indicated by the line thinning to halfwidth). After, half of all trains go to Suburbia, and the other half divert after Beltway to East Suburbia, on a new branch.

But be careful – this technique works well if the short-turn is intended to avoid excess capacity on the extremities of the existing service. If the short-turn is intended instead to increase reliability within the core, then extending those short-turns out onto a new branch may jeopardize that reliability. And make sure to take note of the pitfalls of junctions, below.

Be cautious with reverse branching

Be cautious with reverse-branching, which is when a transit service splits into multiple branches going in to the city, rather than going out. (SEPTA’s Broad-Ridge Spur is a good example of this on-paper. In practice, it’s actually a little more complicated, but that’s a post for another time.)

A SEPTA system map with the Broad-Ridge Spur highlighted

http://www.septa.org/maps/system/

Recall what we went through above: branches are lower frequency than trunks. Reverse-branching into an urban core thus means you are reducing frequency precisely in the area you need it most. 

Note that I say “be cautious,” not “avoid.” I think that one of the major values of crayon maps is that they sometimes value creativity over feasibility. Reverse-branching is usually more creative than it is feasible, but sometimes it sparks good follow-up ideas. So, I wouldn’t forbid it as a hard-and-fast rule, but it’s good to be aware of its drawbacks.

Junctions are complicated

Junctions where branches come together will always have one of two drawbacks, so be careful where you put them:

If a level junction is used, then you will have capacity limits and sometimes delays, as trains need to wait for each other to cross, and may need to leave a whole signal block free (i.e. the train may not be able to wait right at the junction like a car at an intersection, but may need to be hundreds or thousands of feet away).

A flying junction avoids those problems and should be the standard for any new rapid transit junction. However, flying junctions are much more expensive, and also take up more space — horizontally and vertically — than level junctions. So, as with all things, it’s a trade-off between cost and quality of service. If you want your proposal to be taken seriously, make sure your proposal is ambitious enough to merit building the flying junction. 

In conclusion, branches are not your friend

Branches are not the friend of the crayon-mapper. They look great on paper but require a lot of careful planning to be done well; when done poorly, they can be actively detrimental to the individual branches and the system overall. If you really want to use them on a subway network:

  1. No more than two branches
  2. Aim to branch at least 5 miles from the core
  3. Look for segments where there already is reduced service (short-turns) or reduced demand for service (lower density)
  4. If both branches demand full-frequency service, then both branches warrant their own trunklines through the core: i.e. they shouldn’t be branches, but should be separate lines

Post-script on LRT, BRT and mainline rail

All of the dynamics I describe here hold true on other modes of service. However, the cost-benefit calculations work out a little differently because there are different standards for these modes.

LRT

For the most part, LRT is going to have the same struggles as an HRT subway would. The main differences are all knock-on effects of light rail’s shorter and more nimble rolling stock. Shorter trains makes it easier to “fudge” capacity in a trunk line, with multiple trains stopping in a single station at once, and shorter signal blocks allowing trains to run closer together. The shorter signal blocks also mean that flat junctions – while still disruptive – can be mildly less problematic. 

LRT also – by virtue of its lower capacity – is sometimes a better fit for serving lower-density regions, which can sometimes mean that the frequency cost of more than two branches is more manageable, especially if combined with a higher frequency on the trunk than you could achieve with larger trains.

Boston and Philadelphia both run a scheduled 40 light rail trains per hour through their tunnels (Philly apparently swings even more than that), with four and five branches respectively. San Francisco runs at a lower frequency (I think) in the Muni Metro subway, also with five branches. All three of these systems are plagued with reliability and other issues. (Muni recently tried to redirect two of its branches out of the subway, but now has returned them to the tunnel). That isn’t to say that these systems can’t be improved, nor am I denying benefits to their approaches. But it’s probably best to think of these as the exceptions which prove the rules.

BRT

BRT comes in lots of flavors, some of which are more amenable to branches than others. Christof Spieler gave an excellent presentation at TransitCon 2022 on the varieties of BRT, and discussed some of the pros and cons of branching on each. In short, I’d say that the more you want your BRT line to act like a subway line, the more you should follow the same rules about branching. 

Mainline rail

Mainline rail faces all of the same dynamics I outlined above. The major difference is that the costs of branching don’t always end up being “disqualifying.” If you take a 20tph rapid transit line and give it 10 branches, each branch will get 30 minute headways, which no longer is “rapid transit.” But if you give a 20tph commuter rail line 10 branches, the 30-minute headways on each branch may be perfectly reasonable. The same dynamic is at play — it’s just that the requirements are different and therefore the costs are more acceptable. 

On the other hand, some dynamics remain equally if not more problematic. Junctions, for example, will still be disruptive if built flat and costly if built flying. And reverse branching’s impact may be felt even more acutely: many American commuter rail lines run once per hour; split those between two downtown terminals – we’ll call them “Northtown” and “Southtown” –, and commuters now have to wait two hours between trains, which reduces flexibility for riders and may have an overall chilling effect on ridership on both branches. 

Consider this fictional system below:

Inspired by the NJ Transit system, four routes of 2 tph each branch out to Burlington (green), Louisburg (red), Toledo (blue), and Millville (purple). Those last two merge at Arroyo, proceding north to Belleview where they are joined by Red, all three of which proceed to Newtown where they are joined by Green. Between Newtown and Riveredge are 8 tph. East of Riveredge, each line splits into two half-width thinner lines, one each to Northtown and to Southtown

At first glance, it looks like a relatively robust commuter rail network. Each suburb sees 30-minute headways, and that segment between Newtown and Riveredge sees rapid transit-frequencies of 7.5 minutes. And every community sees direct service to both Northtown and Southtown.

But most commuters don’t care about going to two different workplaces – their destination is the same everyday. Let’s look at what the network looks like for a Northtown commuter:

A modified version of the map above, showing only services that go to Northtown. Each line is now half-width all the way through.

This paints a significantly different picture. Most suburbs are reduced to hourly service, and the turn-up-and-go frequencies at Newtown are gone. 

(To be fair, in this example, most American cities would be thrilled to see commuter rail service at this level – hourly commuter rail is nothing to sneeze at. But I’m keeping the numbers simple to keep the math simple; if most cities start with hourly commuter rail, then reverse branching drops the effective frequency of each branch down to every two hours, which is pretty rough. You get the idea.)

Instead of a robust trunk-and-branch network, reverse-branching reduces this network into two significantly diluted networks operating in parallel. 

The same map as above, but for Southtown, shown at 50% size to compare to the Northtown map at right.
The same Northtown map as above, shown at 50% size to compare to the Southtown map at right.