Re: I-90 Interchange Improvement Project (Allston)
What are the peak DMU frequencies we could see on the SS branch? Could it approach anything close to the 7-10 minute headways we see on other lines?
See the discussion on p.14 of this thread about that. Short answer: yes, if we're talking DMU's in a vacuum. 15 minute headways, not 7-10 min. headways...
nowhere is < 10 mins. possible out of South Station when it's at peak load feeding that much traffic into Back Bay. Nowhere did anyone promise promise subway-level headways; that's not what Indigo is, or ever could be.
It gets much more doubtful you can pull this off on the existing infrastructure when you factor in DMU's + a Framingham/Worcester schedule that's going to grow much heavier by its lonesome in the next few years.
Short answer as to why. . .
-- The DMU's are fine by themselves; there's 3 crossovers between Back Bay and New Balance that allow Worcester trains to pass. The DMU's won't be the ones delayed.
-- The problem is Framingham/Worcester and the track situation
outside the scope of this DMU project. Between the west (New Balance) end of Beacon Park and Framingham station there is only 1 set of crossovers at Wellesley Hills for staging train meets. And trains have to hop over each other all day long between Beacon Park and Wellesley when the Newton stops are being served.
-- Certain sequences of Framingham/Worcester trains have very low margin for error on their schedule. It all has to do with trains serving the Newton stops vs. trains skipping the Newton stops, and the single-track platforms in Newton forcing trains to switch tracks. Every X many trains there's an extra-vulnerable slot where the track-switching dance between Beacon Park and Wellesley has to be made spot-on or things go to hell.
-- A vulnerable slot that blows its meet is going to have to pause and wait a very long time for the conflicting train to clear. That is why when Worcester is late, it is late by a mile and you routinely hear horror stories of 30 minute late, 60 minute late trains that sit at a dead stop for 20+ minutes at a switch. When one Worcester/Framingham train is late by a mile it has the added effect of backing up other Worcester/Framingham trains in vulnerable slots. There's no in-between...the line is either on-time or it's a full-on disaster commute. And this vulnerability is at its absolute most precarious at the AM and PM peaks.
-- The only way to fix this is to install new crossovers. One in Newton before Newtonville. One at Riverside Jct. A re-spacing of the one by Wellesley Farms out further into Wellesley. And maybe one more before Framingham. That solves the problem of having too few passing opportunities, lets locals and Worcester expresses coexist in very large numbers, and gives trains that blow their slots lots of recovery time. It's how every other high-traffic line on the system works, and how the
outer half of the Worcester Line works.
-- The signal system is too old and limited to simply retrofit. Extremely expensive and unreliable to perform surgery on. It was considered several times in the past, and every time it projected too difficult. Basically, all 21 miles of signals from Back Bay to Framingham have to be junked and re-laid from scratch to really make it work. Requiring the same total teardown/rebuild job they're doing on the Fitchburg Line today with those weekend closures. Easily $50-75M, with zero funding for that alloted or hinted to in the Transportation Bill.
-- However, mix the full 15 minute headway Indigo service into the mix with the full Framingham/Worcester schedule (which is going to get bigger still in the next 3-5 years) and things get dicey if you don't spend the $$$ for the signal do-over. Something as inocuous as needing to hold open the doors for a couple minutes longer at Back Bay or Yawkey for a ballpark crowd or extra passenger assistance lowers the margins enough that the meets could get a couple minutes out-of-sync between New Balance and Wellesley Farms. And then...delay catastrophe.
-- Not even doubling up the Newton platforms helps much here beyond the fringes, because express trains still have to hop over locals. At most that'll shave off a few trains that won't have to be crunched into a do-or-die schedule meet. There will still be trains crunched into the timing dance between New Balance and Wellesley Farms, and the consequences for blowing those meets will be disaster commute all the same. This doesn't go away until the signals are redone.
-- This is a necessity even if the DMU's
never happen. Within 5 years there'll be enough Framingham/Worcester trains that they'll start scraping up against the ceiling. A couple of Amtrak Inlands will probably force the tipping point for all the signal work $$$ because those won't be able to handle the meets either. The Worcester Line has huuuuuuuuuuuuge untapped capacity if they fixed this. Track 61 DMU's to West, DMU's to Riverside, Framingham locals, Worcester expresses and non-stop superexpresses, Worcester rush hour trains routed down the Grand Junction (the 5 per AM / 5 per PM peak plan in the prior study, not the DMU), Amtrak Inlands, Amtrak Inlands down the Grand Junction, a daily Boston-Montreal round trip. Yeah...it can handle all that if you give it nimble passing opportunities inside Framingham. It wouldn't be too too far removed from the kind of traffic levels the NEC Shoreline used to be able to handle in the slow-speed pre-electrification days. But it's gonna cost them to renew that much track infrastructure. And they haven't said a peep about how/when/for how much.
--
NOTE: New Balance and West, being inside of the Beacon Park crossovers where there's plenty of passing space, should also be fine to add to certain Worcester/Framingham schedules when they're built. Without the signal work. They have minimal effect on the Newton dance at conventional commuter rail schedules. Not enough to degrade the on-time performance to worse than the (crappy) it is now. New Balance definitely is going to pre-date the DMU's by several years anyway. West easily could too, and still be a quite very useful station at conventional commuter schedules (BU will be fetching a lot more of the patronage for the first decade anyway since Harvard land is going to take awhile to build). So keep in mind it's the extra layer of
overlapping services on the schedule that's the destabilizer...not the presence of these extra station stops themselves. The track has to be reconfigured to juggle the
services.
Everything that has to be done here is outside the project area of the DMU service terminating in Allston (Riverside...that DMU service they definitely can't swing without the signals). So if they're not funding the signals/crossovers now or talking about how they're going to make up that $50M+, it comes down to this:
-- You can run the DMU's. The DMU's will never be made late by a Framingham/Worcester train.
-- You can build the stations. The stations can serve the existing schedules years before the DMU's even debut.
-- ...but, are the political consequences of further damage to Framingham/Worcester on-time performance too severe to proceed with the DMU's here before they can fund the signals. The way the Worcester Line is growing, and with how critical a function it's starting to serve on horrendous MetroWest highway commutes...can it realistically happen without addressing the rest of the line? My guess is no given how much representation the Worcester Line gets in the Legislature (for good reason).
-- If that's case, when are we going to get a schedule and funding commitment for the track work? The longer that goes unmentioned, the longer you can push back the rollout of DMU's from South Station to West. This Indigo leg will start to lag well behind Fairmount and Track 61. This is an unavoidable part of the plan...answer whether anything is doable without first fixing Newton-Framingham, then quantify how much that slows the rollout to full 15 minute headways. Because this isn't going to be a well-patronized service if the headways meander at 20-25 minutes instead.
So...we're only getting part of the picture. They can't just stick a podium in front of the site of future West Station and talk about DMU's from West-inbound in a vacuum when all of the most tangible project risks and impacts are outside the city.
And no, I don't think Grand Junction service is ever going to happen. The traffic queue math around the grade crossings is fully available in the last study that got soundly rejected by the locals, and 2 minutes of feeding those timings into a calculator multiplied by simple TPH counts paints a stark picture of what a carpocalypse that's going to be at Indigo-level headways. Try it yourself...it's easy enough for even the most casual observer to do the arithmetic and see how infeasible that's going to be. I'd wager on that extra West platform getting cut from the design quickly and deferred to a later add-on while they back away slowly from that Grand Junction promise.
