Tobin Bridge Relocation/Replacement

[Teban54]

Following up on the Commonwealth Beacon article mentioned above, TransitMatters also published a blog post with more details and analyses:

Where is Chelsea's subway station?

A few quotes from their post:

Regional Rail and Issues with Chelsea's Commuter Rail Station

The station receives trains infrequently (every 30-60 minutes) that take a circuitous route to Boston, is half a mile from downtown Chelsea, and lacks transfers to Chelsea’s major bus routes, the 111 and 116. These inadequacies may explain why Chelsea’s Commuter Rail ridership is modest, at best, despite having one of the densest walksheds on the network. Frequent Regional Rail service will be transformative in many ways, but Chelsea’s Commuter Rail line serves fundamentally different purposes than its overcrowded bus routes, and will still leave key needs unmet even with frequency improvements from Regional Rail.

TL;DR: Regional rail solves some important issues, but not other equally important ones.

Ridership

In fact, Chelsea's transit ridership ranks highly among the entire Metro Boston. If all 14,600 bus riders walked to or transferred at a subway station in downtown Chelsea (similar to Harvard’s role as both a neighborhood stop and a bus hub), it would be among the top 20 rapid transit stations with the highest ridership systemwide, comparable to other major transit hubs such as Forest Hills, Ruggles, Malden Center and Airport. The only stations with significantly higher ridership are: most stations in downtown Boston and the Back Bay neighborhood, as well as Harvard, Central, Kendall/MIT, and Maverick [2].

TL;DR: A "Chelsea subway station" would be a top-tier ridership station, even with today's bus riders alone (and no mode shifts).

Unreliability

The SL3 bus is hampered by traffic in the Ted Williams Tunnel and openings of the Chelsea Street Bridge. The Ted Williams Tunnel is notorious: an average inbound trip across the tunnel should be a 2-minute breeze, but a quarter of buses sit through at least 5 minutes of traffic during rush hours. The Chelsea Street Bridge can open as often as ten times per day, and each bridge opening disrupts SL3 service significantly: the section from Airport Station to Eastern Ave is typically scheduled for 5 minutes, but each bridge opening can lengthen this trip to 20 minutes or more.

Also:

Despite efforts from the MBTA’s Bus Network Redesign (BNR), unreliability persists. According to TransitMatters’ preliminary work on Pokey/Schleppie v2 (to be released soon), “bus bunching [3]” occurs on the 116 more often than any other route as of March 2025, even after recent frequency upgrades under BNR.

TL;DR: Buses suck, SL3 included, and even after the redesign.

Use of Tobin Bridge Replacement: Transit vs. Add-a-Lane

In contrast, adding a transit right-of-way will be a more efficient use of space on the replacement bridge, because transit can move more people in less space than cars can.
[...]
The Manhattan Bridge carries four times as many people by subway as it does by personal vehicles, despite allocating a similar amount of space for both. Likewise, the Longfellow Bridge brings 90,000 riders on the Red Line across the Charles River daily, but only 28,000 cars.

TL;DR: If we're replacing the Tobin Bridge anyway, we should advocate for a transit lane over yet another travel lane.

 

[Equilibria]

As we've discussed on this thread before, though, they don't tackle the question of how this line ties into anything on the Charlestown end. The only plausible link is to Orange (since the Green Line would not meet their standard of being service equal to Cambridge), and I guess I would have hoped that given TM's history of operational analysis they would have addressed that part instead of conveniently stopping their line at Bunker Hill.

 

[F-Line to Dudley]

As we've discussed on this thread before, though, they don't tackle the question of how this line ties into anything on the Charlestown end. The only plausible link is to Orange (since the Green Line would not meet their standard of being service equal to Cambridge), and I guess I would have hoped that given TM's history of operational analysis they would have addressed that part instead of conveniently stopping their line at Bunker Hill.

Orange also wouldn't be equal to the service of Cambridge, being a 9-minute (4.5 x 2) peak headway on a branch vs. a 3-minute peak headway on a mainline. Plus kneecapping the northern OL's frequencies including the big Sullivan and Malden Center bus terminals to the same low frequency.

I mean, there's a good case to be made for the Red X as a source line because doing alternating pairs with the Braintree and Ashmont branches would bring the same mainline frequency to points-north, but you'd have to expand the advocacy to truly grand lengths to get the thru-Downtown portion on the board and probably also get knee-deep in the NSRL CA/T alignment advocacy (which TM has stayed at arm's length on to keep their core Regional Rail advocacy from getting diluted) so the NSRL South/Congress alignment is freed up for the new subway from South Boston. Simply drawing a line at Charlestown and not even speculating about how you're going to get a frequency source there doesn't even provide much grist for an official feasibility study--a necessary first step--let alone an action plan that's going to directly influence the Tobin II's design.

 

[KCasiglio]

I mean, there's a good case to be made for the Red X as a source line because doing alternating pairs with the Braintree and Ashmont branches would bring the same mainline frequency to points-north, but you'd have to expand the advocacy to truly grand lengths to get the thru-Downtown portion on the board and probably also get knee-deep in the NSRL CA/T alignment advocacy (which TM has stayed at arm's length on to keep their core Regional Rail advocacy from getting diluted) so the NSRL South/Congress alignment is freed up for the new subway from South Boston. Simply drawing a line at Charlestown and not even speculating about how you're going to get a frequency source there doesn't even provide much grist for an official feasibility study--a necessary first step--let alone an action plan that's going to directly influence the Tobin II's design.

Yeah the Congress St alignment I think is the obvious (only?) viable path to HRT on the Tobin, but it immediately rases the question of capacity/space between North Station and Haymarket.

 

[F-Line to Dudley]

Yeah the Congress St alignment I think is the obvious (only?) viable path to HRT on the Tobin, but it immediately rases the question of capacity/space between North Station and Haymarket.

Shouldn't be an issue. The Baker tankapalooza 2019 NSRL reassessment that advocated for the 2-track South/Congress alignment said incoherently that we could eventually get 4 Purple Line tracks by building the CA/T alignment in duplicate with separate stations. Which is a ridiculous operational and cost-benefit claim, but does at least more-or-less settle the physical feasibility of the parallel subway digs.

 

[Teban54]

As we've discussed on this thread before, though, they don't tackle the question of how this line ties into anything on the Charlestown end. The only plausible link is to Orange (since the Green Line would not meet their standard of being service equal to Cambridge)

Here are my personal thoughts:

• Green Line branch (C branch extension) from North Station. This is my favorite -- it's a net benefit for everyone and doesn't make anyone worse off.
  • GL's bilevel platforms at North Station and the curve to Lechmere/GLX even provides a natural setup
  • If capacity is a concern, can also extend another branch in the future, such as the B
• Orange Line branch from North Station. A more popular proposal and provides higher capacity to Chelsea, but at the cost of Malden receiving half the trains (every 6 minutes at best, every 9 minutes with current infrastructure).
• Blue Line branch from Maverick. Aligns better with the demographic/cultural needs (between Chelsea and East Boston), but can't take advantage of the Tobin Bridge replacement.
• A brand new line. Costliest of all, but most beneficial in the long term. Possible options after Charlestown are:
  • Another downtown subway trunk, such as following Congress St from North Station to South Station
  • Connect to OL at Community College (for downtown-bound transfers), then become a circumferential route to Kendall, and either Back Bay or Longwood Medical Area
  • Continue down the river bank to Science Park and Charles/MGH, then to either Kenmore or Arlington (GL)

While most of these would have lower capacity than the Red Line, they would all greatly reduce the gap between Chelsea's and Cambridge's service levels that's highlighted here.

And it can be argued that Chelsea may not need full RL-level capacity anyway:

• Chelsea's walkshed population figures are still smaller than RL North (90k)
• Cambridge also draws more reverse-commuters than Chelsea can ever hope for, further boosting its ridership (unless/until the industrial parcels in Chelsea are rezoned)

 

[vanshnookenraggen]

From the article:

One particular irony is that the majority of traffic through U.S. Route 1—the highway that passes through Chelsea and feeds into the Tobin Bridge—does not even originate from Chelsea. MassDOT estimates that 57% of cars on the Tobin Bridge come from points north of the city.

That isn't irony. That's how highway bridges work.

I'm all for adding transit to the new bridge, but it seems that the most effective way to do this is through bus-only lanes that could one day be converted to rail (or dual use?).

 

[JohnCostello]

From the article:


That isn't irony. That's how highway bridges work.

I'm all for adding transit to the new bridge, but it seems that the most effective way to do this is through bus-only lanes that could one day be converted to rail (or dual use?).

I'd much rather see an Orange line subway branch from just before Community College with a stop along Chelesa Street (Now arriving at Navy Yard!) with the current traffic underwater coupled with a subway doing cut and cover all the way to Route 60, then above ground parallel with Route 107 to West Lynn and then over the ROW to Central Square. The Bridge auto traffic could be underground to around Chelsea High. The car tunnel could be shorter to allow for a gradual move left under Admiral's Hill and emerge by Chelsea HS. The Ted Williams does gradual curves, why not this?

The new tunnel should also have a pedestrian component like they do under the Thames in London.

 

[JeffDowntown]

I think a tunnel is a non-starter (unless separate from the bridge) because of the vitality of the Tobin as a hazardous freight route.

HC has not been allowed to use the Tobin since the construction of the City Square approach tunnels. It is part of the Boston core tunnels HC prohibited zone.

 

[vanshnookenraggen]

Been a loooooooong time since I've sharpened my MBTA crayons, but here's my pitch:

Build a branch of the Green Line that connects to the inner loop at Gov't Center that runs along Hanover St, then under the harbor to the Navy Yard.

Now, much will depend on the design of the bridge. But if there is a transitway on the underside, then this could be opened as a busway first, with the tunnel coming second.

Where it goes once it crosses into Chelsea is another can of worms, but I figure that won't matter until we figure out how to integrate this into the overall network.

On the track map, I've labeled this as the C, but given the limited capacity, I think there could be another line which loops at Gov't Center (H). This would mirror many of the north shore bus routes which terminate at Haymarket.

 

[Riverside]

Been a loooooooong time since I've sharpened my MBTA crayons, but here's my pitch:

Build a branch of the Green Line that connects to the inner loop at Gov't Center that runs along Hanover St, then under the harbor to the Navy Yard.

Now, much will depend on the design of the bridge. But if there is a transitway on the underside, then this could be opened as a busway first, with the tunnel coming second.

Where it goes once it crosses into Chelsea is another can of worms, but I figure that won't matter until we figure out how to integrate this into the overall network.

On the track map, I've labeled this as the C, but given the limited capacity, I think there could be another line which loops at Gov't Center (H). This would mirror many of the north shore bus routes which terminate at Haymarket.

View attachment 63945View attachment 63947

Very nice! Some similarities to the 1914 concept:

The lack of an Orange Line transfer is unfortunate. A North End station would be cool, but I wonder if a station at the Greenway with a connection to Haymarket might be valuable.

 

[vanshnookenraggen]

Very nice! Some similarities to the 1914 concept:

View attachment 63959
View attachment 63960

The lack of an Orange Line transfer is unfortunate. A North End station would be cool, but I wonder if a station at the Greenway with a connection to Haymarket might be valuable.

After all these years, I've given up trying to imagine I've ever had a truly original idea. But a good idea somehow always keeps coming back.

The issue with "Haymarket East-North End" station is that the Central Artery Tunnel is in the way:

Now, the tunnel I'm proposing would have to pass under the Central Artery, so it's *possible* that you could put a deep station there and the grade up to the Gov't Center loop isn't too steep. But that does seem like it's asking a lot.

I suppose you could route the new tunnel under the Green and Orange Line, adding in a "Haymarket Under" station (similar to scheme B from the 1914 plans), but then that would bypass the North End.

 

[astroTrain27]

Been a loooooooong time since I've sharpened my MBTA crayons, but here's my pitch:

Build a branch of the Green Line that connects to the inner loop at Gov't Center that runs along Hanover St, then under the harbor to the Navy Yard.

Now, much will depend on the design of the bridge. But if there is a transitway on the underside, then this could be opened as a busway first, with the tunnel coming second.

Where it goes once it crosses into Chelsea is another can of worms, but I figure that won't matter until we figure out how to integrate this into the overall network.

On the track map, I've labeled this as the C, but given the limited capacity, I think there could be another line which loops at Gov't Center (H). This would mirror many of the north shore bus routes which terminate at Haymarket.

View attachment 63945View attachment 63947

Not to get too far ahead of ourselves here, but at first glance, these seems to set you up nicely for Rutherford Ave Trolley that branches off at your new Navy Yard station. It wouldn’t be a particularly direct route downtown, but you’d at least be taking full advantage of the new harbor tunnel.

If you wanted to get really fancy, you could even run a service from branch to branch to give Chelsea a decent connection to the OL at Community College and take full advantage of the Tobin bridge replacement too.

 

[TheRatmeister]

Here's a map with basically any alt. I could either find or think of. I'd almost certainly lean towards heavy rail, it has options that span across the possible cost spectrum.

 

[Longfellow]

Putting my hat in for a west station - grand junction - Tobin alignment with a transfer at Kendall, align somewhere in the inner belt where we can find space to get over to Tobin

 

[Riverside]

After all these years, I've given up trying to imagine I've ever had a truly original idea. But a good idea somehow always keeps coming back.

The issue with "Haymarket East-North End" station is that the Central Artery Tunnel is in the way:

View attachment 63967

Now, the tunnel I'm proposing would have to pass under the Central Artery, so it's *possible* that you could put a deep station there and the grade up to the Gov't Center loop isn't too steep. But that does seem like it's asking a lot.

I suppose you could route the new tunnel under the Green and Orange Line, adding in a "Haymarket Under" station (similar to scheme B from the 1914 plans), but then that would bypass the North End.

Well, and to be fair to you, your idea includes the North End component, which wasn't a priority (or even a thought?) in the 1914 plans.

But yes -- I figured "in for a penny, in for a pound" in terms of a Haymarket station under the Central Artery; you're gonna need to tunnel under there anyway.

Here's a map with basically any alt. I could either find or think of. I'd almost certainly lean towards heavy rail, it has options that span across the possible cost spectrum.

Nice work!

I wonder if a light rail elevated along Congress St in downtown would be a total non-starter. The old Central Artery created a substantial physical barrier that cut off the North End, but a modern el with a slimmer footprint that goes through downtown proper seems like it could be different.

 

[Nexis4jersey]

Why not just build a branch off the Orange Line. A Green line extension would require a harbor tunnel to reach Charlestown or an expensive viaduct addon near Lechmere which would have to deal with I-93 , commuter rail tracks + the Orange Line. I would branch off before Community College with a station under the heart of Charlestown and then over the Tobin and to Everett.

 

[F-Line to Dudley]

Why not just build a branch off the Orange Line. A Green line extension would require a harbor tunnel to reach Charlestown or an expensive viaduct addon near Lechmere which would have to deal with I-93 , commuter rail tracks + the Orange Line. I would branch off before Community College with a station under the heart of Charlestown and then over the Tobin and to Everett.

Because it would halve frequencies to the big Sullivan Square and Malden Center bus terminals, at cascading ridership losses to the 22 affected bus routes that transfer there. And no destination on the branches would achieve better than 9-minute peakmost headways, the worst headway target on the rapid transit system.

All of the potential ridership/transit shares in TransitMatters' population density calculations would have to be adjusted down for Orange vs. any other source.

 

[TheRatmeister]

And no destination on the branches would achieve better than 9-minute peak headways,

Any bridge replacement is probably far enough out that we could speculate 6-8 minute headways on the branches but the point doesn't really change. Both branches need better.

 

[CheapLeak]

Thought I'd throw my hat in the ring with a (very rough) diagram with my proposal—converting the 111 to LRT (or BRT).

This would use the brattle loop and its tracks before descending to new, deeper platforms at Haymarket, with a corridor to the rest of the station. I can't determine how this would be done for here and beyond, but likely TBM and mining. Would be a stop somewhere in the North End before entering Charlestown, then (somehow) surface, stop, and rise onto the new bridge. It would then use it's own ROW to dive down to Chelsea's Broadway, before then just following the 111's route to Woodlawn, before then following Elm Street to a terminal at/near Ferry Street, with a transfer to a Broadway HRT.

The main reason for this is simply due to its high ridership, which should benefit from it. The main complication is lack of dedicated ROW. Bus lanes would be converted/moved to the center of the street where they exist. New ones would have to be made somewhere, although I don't really see any good spots, unless we want to ban parking on sections. This makes BRT more appealing, since it could deal with traffic better. It could be technically ran as a traditional, mixed-traffic streetcar, but I don't know if that's worth it over just keeping the 111 the way it is. More so a crazy transit pitch than the rest of these, but whatever.