Sunday, August 9, 2015

Quick Allston update

I've had some questions about my Allston plans along the lines of "how steep do the slopes need to be to match the grade of the Worcester Line and Grand Junction Line at the proposed West Station?" There have also been concerns about the grade of the Grand Junction rising from beneath the BU Bridge to ascend over the Turnpike.

The answer to the first question is: not very steep. I've gone over the grades before but have illustrated it in somewhat more detail below. It's perfectly feasible with a 1% grade; basically, you have about 1100 feet for the two lines to meet, and one can ascend while the other descends. This would put the grade of the track in the station at 14 feet—slightly lower than the current railroad—and about 10 feet lower than the adjacent streets in the BU Campus.

[Quick clarifying update on the above chart: dashed lines for the Grand Junction and Turnpike show areas where their alignments are outside of the constrained right of way area; for the Grand Junction, across the BU Bridge, and for the Turnpike, towards the toll plaza.]

The long and short of it is that the further west you move West Station, the lower it can sit. If it were moved to Cambridge Street, it could be at a grade of 0 feet, well below the current grade, although it would be much further from the core of the BU Campus. Wherever it is is a compromise: further east is higher (really anywhere west of Ashford Street would be a split-grade station with ramps or stairways between the two lines) and further west is lower. It would also be possible to have the Grand Junction in the center and the Worcester Line split on the outside; this might be preferable to easily enable cross-platform transfers. NB: Drawing not to scale:


  1. Is the vertical thickness of the Grand Junction viaduct expected to be about 8' or 9', given that the diagram seems to show the railhead 23' or 24' above the Interstate highway surface and we need less than 15' of clearance from the bottom of the bridge to the highway surface? And would putting the vertical supports on both sides of the bridge instead of only at the middle reduce the thickness of the bridge?

    I've been wondering if building a transit way as a northward extension of Babcock St would be feasible, with it continuing into the median of a relocated Soldiers Field Road to N Harvard St. With such a configuration, several services that originate at Harvard and continue to West Station would be possible; I'm thinking the places these could continue to past West Station might include:

    the portion of the B branch to the west of Babcock St

    the portion of the B branch from Babcock St to the vicinity of the BU bridge, then follow at least part of the current bus route 47 toward Longwood

    along Babcock St to Coolidge Corner, and then several routes from there: C branch to Reservoir; Longwood Ave; mirror part of the 66 and then part of 39 to end up at Forest Hills; mirror part of 66, a bit of 39, a bit of 14, and then most of 22 to end up at Ashmont

    It seems like depressing the west end of I-90 in the constrained corridor by 5-10 feet below what is in your diagram, or figuring out how to build a thinner viaduct, or going for a slightly steeper railroad grade might improve a Babcock extension transit way environment.

    West Station also ought to have a BRT like bus station for highway buses (with passing lanes) designed so that a bus going along I-90 can stop at West Station with a minimum of extra distance traveled and time spent as a result of making the stop; it might make sense to make the bus station in each direction be accessible from the left lane (with the bus station getting 60' - 100' in between the eastbound mainline lanes and the westbound mainline lanes), and then have all of the Soldiers Field Road etc ramps in the right lane, to limit how much any merge friction involving Soldiers Field Road impedes the flow of buses. The design of the I-90 bus platforms should probably be such that the only way for a bus to exit the bus station is to resume traveling along I-90 in the same direction the bus was going when it entered the bus station. The goal would be to make the I-90 bus platforms work well enough that all of the intercity buses and MBTA express buses that travel along that part of I-90 would stop there.

  2. I'm looking at the steep incline of the current turnpike elevation, and I'm assuming the current preferred alternative of keeping the highway on top will have a similar profile: In such a case, the 'elevated highway' alternative will require thousands of cars to drive up a steep grade every day for what - the next 50-75 years. This burns a lot of gas and emits a lot of CO2. In contrast, the 'rail on top' alternative you propose has a very flat overall profile... much less CO2 emitted per unit time.

    I wonder if there is a way to quantify the two alternatives in terms of greenhouse gasses. MassDOT and the Commonwealth have greenhouse gas emissions goals after all. I wonder if, when numbers are run comparing the net deltas in energy required to lift all those single occupancy vehicles over a rail line against raising the rail over the highway, there is a substantial difference in the release of CO2 into the environment. My guess is yes, elevating the train will have a much lower carbon footprint. I hope that can strengthen the argument in favor of elevating the train.

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