Tobin Bridge Relocation/Replacement

[F-Line to Dudley]

Interestingly, I would have been concerned about GLX Medford branch exceeding capacity on Day 1, given its extremely dense walkshed (80k compared to RL North's 90k). But while anecdotal reports suggest that E trains are packed, its ridership is still much smaller than RL North, and comparable to each individual GL streetcar branch, despite much faster grade-separated service to downtown.

Do we know that for sure when fare collection enforcement on GLX has been...intermittent at best...since launch? I suspect that what ridership has been tallied so far has a rather severe undercount.

 

[TheRatmeister]

Do we know that for sure when fare collection enforcement on GLX has been...intermittent at best...since launch? I suspect that what ridership has been tallied so far has a rather severe undercount.

I suspect you are correct. Going through the data for the green line which is collected with APCs (I think?) rather than station entries leads to... interesting results. It suggests for example that every surface E branch station along Huntington Ave had less than 1000 daily average boardings in Fall 2019. Either that or that Boylston had more than 1.5 times as many boardings as gated entries. That's why I use the 2013 statistics instead because there is really nothing better.

 

[vanshnookenraggen]

I guess the bigger question is: Does the "ease" of connecting to the Brattle Loop and a Charlestown station make it more advantageous over building a very expensive FJ at Maverick and the difficulty of tunneling in East Boston and Chelsea? Picking Green over Tobin means you mostly have to go with elevated rail in Chelsea which reduces cost once you get there too. I'm also a bit concerned about Chelsea ridership exceeding capacity on Day 1.

Yes, but that's more so because a FJ at Maverick is a terrible idea. If you *must* branch the Blue Line, do it after Airport and have it follow the old Grand Junction in a tunnel to Chelsea. But as has been pointed out, this will screw over the rest of the riders up to Wonderland. If Red-Blue is built, and maybe CBTC signals go in, you can probably get away with splitting service if you can boost capacity to 30tph. Even so, that is limiting for any extension to Lynn.

A Green Line branch doesn't mean elevated in Chelsea at all, although this is obviously going to be based on the route. My preferred route is up Everett Ave to the Revere Beahc Pkwy. The avenue is wide enough to build out a median (probably have to take some land but not buildings), or build a cut and cover tunnel.

If you're talking about going along Broadway instead, you probably aren't using the new Tobin at all.

 

[Tallguy]

So, I believe that service is every 5 minutes now. If you increased to every 3 minutes on the trunk, then each branch would get 6 minute service. One crossover every 6 minutes is not beyond the capacity of a flat junction. That's why there is provision for one at Maverick.

 

[Riverside]

Obviously I'm no civil engineer, but the clearance under the bridge is 135 feet. At 6% grade, that's, like, 2250 feet of running distance and 2254 feet of incline... right? (I'm always unconfident in my own arithmetic.)

I want to circle way back to this. From what I can tell, the clearance under the Tobin today is 135 feet. At 6% grade, that's 2250 feet of running distance. To the north, that would extend to 2nd St:

(And this assumes rise from sea level; the actual starting point of an elevated would be significantly higher.)

To the south, from the Little Mystic Channel, 2250 feet runs to Prospect St.

Even rising to 150' of clearance over the water would require 2500 feet of running distance, which is the limit of 6% grade for light rail (although, again, 150' over water ≠ 150' from street level).

Based on these figures, I see absolutely no reason that a light rail line couldn't run over a bridge of similar dimensions to the Tobin. Conventional heavy rail would be significantly more difficult: 3.9% grade to reach 135' requires a bit under 3500 feet of running distance, which puts you between 4th and 5th St in Chelsea and Warren St in Charlestown. But even then, that is not intractable if you really wanted to run heavy rail. You'd likely lose intermediate stations in Charlestown and near Admirals Hill, which I think would be a significant value loss, but I could understand the argument in favor of that if you really wanted extra capacity.

As I said previously, I'm not a civil engineer, so I'm happy to learn why it's not so simple as what I've laid out above. But, absent that, I see no particular reason for concern.

 

[TheRatmeister]

3.9% grade

That's a pretty conservative estimate. If we're assuming that any line over a new bridge is a standalone line, it will need new rolling stock which can be designed beefy enough to take steeper grades. Yes it is more expensive on the rolling stock procurement side, but likely far cheaper on the bridge side.

 

[JeffDowntown]

That's a pretty conservative estimate. If we're assuming that any line over a new bridge is a standalone line, it will need new rolling stock which can be designed beefy enough to take steeper grades. Yes it is more expensive on the rolling stock procurement side, but likely far cheaper on the bridge side.

Generally the next step up for grades is a cog railway or a cable-assisted loco. Effective but very slow. Also lots of maintenance (lots of mechanical wear and tear).

 

[TheRatmeister]

Generally the next step up for grades is a cog railway or a cable-assisted loco.

Not from 4%. 6% is roughly the next step up, and is absolutely doable with (beefy) subway trains.

 

[F-Line to Dudley]

Not from 4%. 6% is roughly the next step up, and is absolutely doable with (beefy) subway trains.

Rubber-tyre metro if you want to avoid hideously overpriced custom equipment. Probably not something the T is ever going to consider, though, from the lack of maintenance continuity with the other 4 lines.

 

[Charlie_mta]

Not from 4%. 6% is roughly the next step up, and is absolutely doable with (beefy) subway trains.

How about an elevator at each end of the main span of the new bridge, sort of like a lift bridge mechanism, which would raise or lower a consist of transit cars from or to the ground level.

 

[F-Line to Dudley]

How about an elevator at each end of the main span of the new bridge, sort of like a lift bridge mechanism, which would raise or lower a consist of transit cars from or to the ground level.

Or...you could just not do ANYTHING unorthodox and route a transit line out of Somerville or Eastie or in a tunnel instead of tying oneself in knots trying to make the Tobin work. Absolutely nothing says it HAS to be an over-Tobin alignment that serves these communities.

 

[vanshnookenraggen]

Or...you could just not do ANYTHING unorthodox and route a transit line out of Somerville or Eastie or in a tunnel instead of tying oneself in knots trying to make the Tobin work. Absolutely nothing says it HAS to be an over-Tobin alignment that serves these communities.

This. The Tobin route is a bad one for many reasons.

 

[Riverside]

4% is the conservative estimate. In the worst case scenario, if there was no choice but to use Red Line rolling stock, then the crossing appears to be doable, albeit with a much longer span (and fewer stations).

As I have mentioned a couple of times now, the naive math suggests that light rail should be perfectly capable of crossing the Mystic with 135 feet clearance at a 6% grade. No apparent need for rubber tire trains or anything atypical.

@F-Line to Dudley, if you have anything to back up your claim that the grades would be a problem, I would love to hear it.

I’m not married to the Tobin alignment by any means. But it would be nice if this discussion could be grounded (no pun intended) in specific details and data.

 

[TheRatmeister]

Generally the next step up for grades is a cog railway or a cable-assisted loco. Effective but very slow. Also lots of maintenance (lots of mechanical wear and tear).

How about an elevator at each end of the main span of the new bridge, sort of like a lift bridge mechanism, which would raise or lower a consist of transit cars from or to the ground level.

Rubber-tyre metro if you want to avoid hideously overpriced custom equipment. Probably not something the T is ever going to consider, though, from the lack of maintenance continuity with the other 4 lines.

Again, you do not need any of this for 6%. If we were talking about 10% that would be a different discussion, but we're not. If high-floor "Light rail" vehicles can do it, then you can have subway trains that do it. Or just build a high-floor "light rail" line/medium capacity metro.

 

[JeffDowntown]

Again, you do not need any of this for 6%. If we were talking about 10% that would be a different discussion, but we're not. If high-floor "Light rail" vehicles can do it, then you can have subway trains that do it. Or just build a high-floor "light rail" line/medium capacity metro.

The biggest problem I see with the long, 6% grade approach is you end up not servicing the significant potential rider base near each end of the bridge. Or you have to try to site stations way up in the air with very expensive access issues (and the stations themselves need to flatten out the grade, extending the run). Big population centers in Charlestown and Chelsea live or work close to the bridge.

 

[Riverside]

The biggest problem I see with the long, 6% grade approach is you end up not servicing the significant potential rider base near each end of the bridge. Or you have to try to site stations way up in the air with very expensive access issues (and the stations themselves need to flatten out the grade, extending the run). Big population centers in Charlestown and Chelsea live or work close to the bridge.

I think this isn't really true. 6% puts the base of the incline at 2nd Street in Chelsea. Note again that this is the sea-level base of the incline; ground level will be higher, and the rail ROW will probably already be elevated at that point. So the actual incline could probably start a bit further south, which also helps ameliorate the cost of flattening the grade along the platform. (It looks like ground-level in Chelsea is about 20' above sea level in that area.)

I think 2nd Street is a perfectly good location for a station. If anything, siting a station slightly northeast might be better. You also wouldn't want to put the station that much further south, since your 10-min walkshed is already bumping up against the water.

You do lose out on access to Admirals Hill if that's where you site the station. But, it's a hill (looks like about 85' high on the side near Tobin); diverting the ROW off the bridge for a short jaunt to a modestly elevated station might be feasible. But losing Admirals Hill isn't a problem unique to a Tobin alignment -- a Grand Junction or Eastern Route line won't get there either.

Charlestown, I grant, is a bit harder. In the above examples, I assumed 135' clearance over the Little Mystic, which pushes a station as far south as Prospect St, which I agree loses a fair amount of potential riders. That being said, the current Tobin has 100' clearance of the Little Mystic, which would only require 1670 feet running distance of incline, putting a station between Vine St and Bunker Hill St, which is better but not by much.

If you assume the station is elevated 20' (which doesn't seem unreasonable), you can push the station north of Vine St. At that point, I do think the walkshed is reasonable:

And as you can see, we start bumping up against the water again, which means that siting a station further north actually doesn't get you as much as you'd think (though yes, Spaulding's presence is notable):

Sorry for all the TED Talks here, folks. Like I said, I'm not married to the Tobin alignment or anything. But I feel like I'm operating on a significantly different set of facts than some of you, and I genuinely have that "Am I crazy?" feeling. Am I missing something obvious?

 

[JeffDowntown]

I think this isn't really true. 6% puts the base of the incline at 2nd Street in Chelsea. Note again that this is the sea-level base of the incline; ground level will be higher, and the rail ROW will probably already be elevated at that point. So the actual incline could probably start a bit further south, which also helps ameliorate the cost of flattening the grade along the platform. (It looks like ground-level in Chelsea is about 20' above sea level in that area.)

I think 2nd Street is a perfectly good location for a station. If anything, siting a station slightly northeast might be better. You also wouldn't want to put the station that much further south, since your 10-min walkshed is already bumping up against the water.

View attachment 66496
View attachment 66495

You do lose out on access to Admirals Hill if that's where you site the station. But, it's a hill (looks like about 85' high on the side near Tobin); diverting the ROW off the bridge for a short jaunt to a modestly elevated station might be feasible. But losing Admirals Hill isn't a problem unique to a Tobin alignment -- a Grand Junction or Eastern Route line won't get there either.

Charlestown, I grant, is a bit harder. In the above examples, I assumed 135' clearance over the Little Mystic, which pushes a station as far south as Prospect St, which I agree loses a fair amount of potential riders. That being said, the current Tobin has 100' clearance of the Little Mystic, which would only require 1670 feet running distance of incline, putting a station between Vine St and Bunker Hill St, which is better but not by much.

If you assume the station is elevated 20' (which doesn't seem unreasonable), you can push the station north of Vine St. At that point, I do think the walkshed is reasonable:

View attachment 66497
View attachment 66498

And as you can see, we start bumping up against the water again, which means that siting a station further north actually doesn't get you as much as you'd think (though yes, Spaulding's presence is notable):

View attachment 66499

Sorry for all the TED Talks here, folks. Like I said, I'm not married to the Tobin alignment or anything. But I feel like I'm operating on a significantly different set of facts than some of you, and I genuinely have that "Am I crazy?" feeling. Am I missing something obvious?

That Charlestown stop placement is much better for tourists that residents.

You have high density residential (Bunker Hill Development, Domino Development) and high density employment (yes Spaulding, but also the massive MGH research campus with several thousand employees) out at the far edge of your walkshed. Charlestown would really be better served with a plan that creates 2 stops on that line.

 

[Riverside]

That Charlestown stop placement is much better for tourists that residents.

You have high density residential (Bunker Hill Development, Domino Development) and high density employment (yes Spaulding, but also the massive MGH research campus with several thousand employees) out at the far edge of your walkshed. Charlestown would really be better served with a plan that creates 2 stops on that line.

Yeah, like I said, Charlestown is harder.

The MGH campus would be 5 minutes from a station at Vine St, less if you can find a way to cross over/under the apartments. (And a stop at Medford St wouldn't be any better.)

Spaulding is 10 minutes:

The far end of Bunker Hill Housing (I believe) is 8 minutes (and again Medford St does no better):

425 Medford will be pretty far from a Tobin line no matter what. By my measurement, a station at Medford St would be a 17 minute walk, while one at Vine St would be 18 minutes. Either way, I would imagine that site would be more oriented toward Sullivan Square anyway.

Vine St and Medford St are less than 1000 feet apart. Medford St is closer to Spaulding and to some residents, but it also loses half of its walkshed to water. Requiring that station be sited at Vine St rather than Medford St doesn't seem like it should be so detrimental as to undermine the value of the project overall.

 

[The EGE]

Exactly how certain are we that the Tobin replacement is even going to be a bridge? Tunnels aren't cheap, but neither are mile-long bridges.

 

[clam]

How about an elevator at each end of the main span of the new bridge, sort of like a lift bridge mechanism, which would raise or lower a consist of transit cars from or to the ground level.

the prt/monorail mob are going to go nuts with this one