The Commonwealth of Massachusetts is mostly finished with a $300 million rehabilitation of the Fitchburg Line, which will yield more capacity on the line and faster speeds on the longest in-state line in the system. At the same time, the Green Line extension project has seen exponential growth in cost, mostly due to bizarre contracting methods and poor oversight. But it's still a complex project. And now an idea is being floated to cut back a branch of the line to Union Square in Somerville—a branch which parallels the Fitchburg Line—which is in dire need of better transit.
But maybe this presents an opportunity for some out-of-the-box thinking. Both branches of the GLX are slated to be built alongside existing Commuter Rail lines, and building next to an active railroad is not particularly easy. There are safety concerns, FRA issues, and even the cost of staff to insure the safety of workers—and the safe passage of trains—comes at a significant cost. If you could cut all parallel rail service, you could save a lot of time and money: rather than having to rebuild in a constrained corridor, you could more quickly build the project in a much easier work environment.
This, of course, would require cutting Commuter Rail off from the the terminal in Boston. For Lowell, this is a non-starter: busing from Winchester or West Medford would be subject to the whims of traffic on I-93, as would buses from Anderson/Woburn. And the Lowell Line also serves Amtrak and some Haverhill trains which bypass traffic on the single-tracked portions of the Haverhill Line. At busy times on this line, there is a train every ten minutes.
But for Fitchburg, this presents an opportunity. Before getting to Boston, Fitchburg Line trains stop at Porter Square. Already, between 30 and 50% of Fitchburg riders begin or end their Commuter Rail trip at Porter, transferring for a trip to Harvard, Kendall or even in to Boston. What if, for a short period of time, you closed the line inbound from Porter to allow for reconstruction, and had everyone transfer at Porter?
While this would be inconvenient for some riders, and put a bit more of a load on the Red Line, it might save a lot of time, and a lot of money, in the construction of the Union Square portion of the Green Line extension, as well as the portion near Lechmere where the branches meet and cross over the Fitchburg Line. Shuttle bus service could be provided between North Station and Porter (a 20 minute ride) but most passengers would take the Red Line. Considering that nearly half the riders already get off, and most jobs downtown are located near or south of the Red Line (in the Financial District and Back Bay) this would be only a minor inconvenience for them. With faster track speeds on the Fitchburg Line, in fact, it might actually be a wash for many commuters.
Using GTFS, I've tested out a few test trips from South Acton:
+16 minutes to North Station
42 minutes via North Station
58 minutes via Porter, Red Line and Green Line.
+6 minutes to Seaport
66 minutes via North Station and #4 bus
72 minutes via Porter, Red Line and Silver Line
+5 minutes to Copley
56 minutes via North Station and Green Line
61 minutes via Porter, Red Line and Green Line
+3 minutes to Park Street
52 minutes via North Station and Green Line
55 minutes via Porter and Red Line
0 minutes to LMA
72 minutes via North Station and Green Line
72 minutes via Porter, Red Line and #47 bus
0 minutes to South Station, Kendall and Harvard
58, 48 and 42 minutes via Porter already faster than via North Station
It's a wash for most commuters other than those traveling to North Station, and most commuters' final destination is not at North Station, but somewhere to the south (since North Station is mostly surrounded by highway ramps and water). In the long run, running trains to North Station makes sense. But if service could be curtailed at Porter for a year to save millions of dollars, I think it is a worthy sacrifice.
In addition, service on the Fitchburg Line could increase in frequency. Each train terminating at Porter would save 20 minutes of round trip running time. This could be translated in to an extra trip in each rush hour to help spread the load, and an extra midday and evening trip as well using the same equipment. It would also be a good opportunity to, once and for all, construct high-level boarding platforms at Porter to allow faster boarding of trains at the station. The two-track station would be more than adequate for the current schedule on the Fitchburg Line, and during the midday, trains could be stored on the tracks beyond the station well shy of construction in Union Square.
The five train sets currently stored in Fitchburg would be enough for full service on the line; the first train arrives in Porter at 6:40 and could easily make the outbound run to Littleton for the 8:20 service back to Boston in the morning. In the evening, the first outbound train to Littleton could easily turn back to Boston in time for the late local departure at 6:20 (which could be pushed back a few minutes with no ill effect on passengers).
With the route mostly cut off from the network, light maintenance would have to be established somewhere along the line (perhaps at the maintenance of way facility near Alewife). For heavier maintenance, trains would have to be shuttled to Lowell across the Stony Brook line from the Willows. This railroad is slow and would need improvement for anything but occasional moves (if it were faster, it could host passenger service from Fitchburg to Boston via Lowell) but would likely be adequate for short-term moves. The extra crew costs would be offset by the savings of rebuilding the inner part of the line quickly and economically.
Is there precedence for this? There is. From 1979 to 1987, the Southwest Corridor was rebuilt below grade between Hyde Park and Back Bay for the relocated Orange Line. The issue was that the Needham Line was only accessible via the corridor. Rather than keeping a track in service and continually moving it around for the rest of the rebuild, they shut down Needham service, replaced it with express buses (which encountered less traffic on the Turnpike than they would today) and rebuilt the corridor in place, That project is obviously larger than the Fitchburg project, and necessitated a longer shutdown, but there are certainly similarities which could yield similar cost savings. See page 202 here.