I really see no reason to handicap such a line by using the Brattle loop. You could run elevated rail over Rt 1 for most of the same effect, then head over N. Washington St for a surface or elevated terminus next to Haymarket. That could at least be high-floor light rail or even full subway rather than being tied into the Green Line.
Fair point. I originally had this as an extension of a GC terminating line, but separated it after. Not fully sure if that's preferable to just having separate lines with a transfer in hindsight though.
Something like this along the NE Expressway (Rte 1 from the Tobin to Rte 60) would be sweet:
My question is what clearance height do you have to provide over the Mystic, and can you get to that height with heavy rail compatible grades under the highway span?
From the T's CRRC vehicle specs, these are the maximum grades for HRT in Boston:
Height, sure. Straddling? Probably not. The slim supports of modern concrete viaducts could easily fit in the ~15' of shoulder space on Rt 1.
Agreed. Everett is the clear winner of the 3 options. However, it's still worth keeping in mind that routing an Everett subway via the Tobin only really works well if the line continues into downtown. If you connect it to the Grand Junction instead, it ends up adding ~7-8 minutes to every trip from Everett compared to following the old El over the Mystic which is... not ideal.
I don't think I can agree here. Revere Center is a strong-ish node but the rest are quite mediocre. If you'd rather hit Revere Center than Woodlawn, it seems like diverging from Rt 1 at Revere Beach Pkwy is a better way to do that. A short tunnel could take you under Revere Center before re-surfacing to terminate at Wonderland.
No doubt it's mostly residential, but the strong ridership of the 111 would seem to suggest that this is fine, actually.
Yes the Everett Branch looks like the best branch to build, but is Tobin really the best crossing for it? If you instead crossed the Mystic near Assembly where the commuter line crosses, you could do so on a much lower bridge upstream of the port facilities and pick up Entourage and the new soccer stadium on the way. (This could be built either as an Orange Line branch from Sullivan Sq or Assembly, or as separate line with OL connections.)
The bridge itself almost always is built parallel to the current structure, with potentially some minor (or perhaps not so minor) land taking near the interface with the approach ramps. Any parts of the span that are stacked highway need to be rebuilt parallel to the current structure.
The approach roads are stacked, so it won't be possible to switch traffic to one side or the other while one level is being demolished and rebuilt. I'd say close the bridge for a couple of years and just build the new structure in the same place on the same footprint.
Where does all the traffic go then? The Tobin carries 85,000 cars per day and obviously there’s no clear transit alternative on the alignment. There’s no way the Revere Beach Parkway can handle all that traffic.
Not much steeper. Up to 6% for 2500 ft., 4% at unlimited length per the GLX Design Criteria Manual. That's compared to 4-5.6% at very restricted length under HRT. The problem is that the current Tobin's grades exceed that...both the maximum grade and the sustained grade. You're not likely to get a rail line on there at all unless Tobin II is engineered with very different grades than the current span, because of the likelihood that the approaches will exceed the max length of the max rail grade. Rubber-tyre metro is the only high-capacity mode whose grades will fit on a bridge that has more than 2500 ft. of 6% interstate highway -standard max grades, and that of course prevents any graft-on to any part of the existing rapid transit system.
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.)
You would be correct. There's also the fact that GL/OL/RL rolling stock isn't the only thing available. (From my understanding) just about any subway car could be juiced up to handle higher gradients. Obviously this is usually more expensive than just, not having higher gradients, but that's probably not the case here because of the fixed bridge height.
The specific issue is steel-wheel braking performance on slippery rail, which is a function of how many axles and how much weight the train has. The feds go with generic reference cases for their recommended standards, the T goes with its actual maximum car counts running empty consists but never exceeds the fed guidelines. It's not an easy thing to reengineer around, because it's extremely invasive to add more axles to rolling stock (with massive downsides in increased power output, maintenance complexity, rougher ride, and much-increased wear on the track). The reason rubber-tyre metros can take almost double the grades is because rubber has lots more friction than steel on a surface, and those trains have many more axles than steel-wheel trains to better distribute the weight on air-filled tires.
I return to the question I raised earlier, would rail on a draw (lift) span under the highway span be unbearable? How often is the 135ft. clearance needed? Would needing to open the span occasionally really be that disruptive to transit performance?