Wednesday, August 19, 2015

Allston: Let's look for a win-win

This is a straight quote from Fred Salvucci about the Allston viaduct: instead of talking about shared pain, we should talk about a win-win. He also referred to my plan as "genius" (or maybe me as a genius, I am too verklempt). Anyway, talk amongst yourselves; I'll give you a topic: here are a couple of updates regarding some technical-ish aspects of the Allston project, to address a couple of concerns I've heard from some people.

1. There won't be a direct yard lead from the Worcester Line trackage east in to the train stabling yard. The answer is … yes, probably, let's talk about it further. In the previous iteration, I had the Grand Junction viaduct descending from to West Station at the same time as the Worcester Line ascends. The issue is that for a Worcester yard lead to leave the Worcester alignment, it needs to stay fully at the base grade until the end of the "throat" section before crossing under the Grand Junction.

So, how do we do this? Well, first, the Grand Junction viaduct needs to continue at its grade (24' above grade) for about 50 more feet to allow the railroad track to pass under it, feasible with no more than a 1% grade. And the Worcester Line would need to proceed at its grade (0') to the end of the viaduct, before ascending to the station and assume a low grade beyond since it will be made for low-speed yard moves (let's assume 0.5%). This all works (although the yard may have to be dug out a bit lower, which will be better for eventual air rights). I discussed crossing one of the Worcester Line tracks under the Grand Junction recently, to allow for island platforms and easy transfers.

The issue is that then the Worcester Line would have to ascend to West Station, and it would have to do so at a higher grade, in this case, 1.5%. However, I think this is feasible. There is currently no freight east of the Beacon Park area on the Worcester Line. 1.5% is steep for passenger trains, but there is a mitigating factor: it would be traversed uphill by trains decelerating westbound to West Station, and downhill by trains accelerating eastbound from the station. So the gravity would actually aid the trains in and out of the station.

Here's a drawing:

2. There is a question of the support structure for the Grand Junction viaduct. I am not a structural engineer (as I've said before), and it's certainly a possibility that the single center posts would not be sufficient to support freight rail. This could be mitigated with supports on both sides of the eastbound Turnpike. While not as elegant as the single post design, it's quite possible that it would be required for 150-ton freight railcars and heavy rail passenger trains. This is obviously something that needs further study.

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