North South Rail Link schematic showing current train volumes for Commuter Rail
lines, potential future RER-style connections and new and existing stations.
Efficiency. The crux of the issue is that MassDOT wants/needs more space at South Station (and eventually North Station) and is limited by the number of tracks. Turning trains around is time-consuming: you have to unboard (deboard?) the train, board the train (even at rush hour, 50-100 or more reverse commuters may be waiting), have the crew change ends, and then thread out the same slow trackage you came in. Even with the best of practices, a terminal station track can only accommodate a train every 15 minutes or so. But if trains run through, boarding and alighting is faster and easier, there's no need for the crew to change ends, and with more destinations, fewer passengers get off at each stop. You could route 20 trains per hour per track, meaning that four tracks in the rail link could do the work of 20 at South Station (currently there are 13; the expansion would add about a half dozen more).
Electrification. You need to electrify the whole system (and maybe Amtrak to Portland). Maybe you could get away with dual mode engines, but that's lipstick on a pig. Electrification of the Commuter Rail network would cost somewhere in the neighborhood of $1 to $2 billion dollars. Not cheap. But huge operational efficiencies: electric trains are cheaper to run, cheaper to maintain, and have faster acceleration meaning that trip times (and staff costs) are shorter, while ridership is higher (faster trains = higher ridership).
North/South imbalance and the Grand Junction. The idea behind the North South Rail Link is that trains coming in to South Station run through the tunnel and out one of the North Side lines. This is the Philadelphia model. This works well in theory (some passengers would get a one-seat ride; others would have to change), but in practice more trains run in to South Station than North Station (although this was not always the case; in 1972 there were twice as many passengers at North Station). Several pair off relatively well:
Needham-HaverhillBut falls apart when you realize that all the North Side routes are taken and you haven't accounted for the Worcester or Fairmount Lines. You could route them through to other terminals, say, to Anderson Woburn, but this seems wasteful; you don't need a train every 8 minutes inbound from Woburn. This is where the Grand Junction comes in. If it were grade-separated in Cambridge (or maybe even if not; there are grade crossings in downtown Chicago with 20 trains per hour at peak times), Worcester Trains could split off at West Station (hopefully) and make a loop (much like lines in Melbourne, where a similar imbalance existed), serving Yawkey, Back Bay, Downtown and Kendall. As for the Fairmount Line …
Old Colony Lines-Eastern Route
Potential for RER(/S-bahn/Crosslink)-style service. Having the rail link in place with the Grand Junction connection would not only allow you to route trains through the city, but it would also allow you to implement RER-type service filling much of the urban ring and providing more frequent service than Commuter Rail (although Commuter Rail could run more frequently as well). If all the paired lines shared one set of tunnels, the Worcester Line could share the other with the following RER-type services:
Allston to Assembly via Cambridge (Kendall) and SullivanThese would operate frequently all day, every 10 to 15 minutes, allowing transfers between subway and Commuter Rail. This leverages the capacity of the rail link to create a complementary urban rail network to provide new connections and take some pressure off the existing hub-and-spoke network.
Readville to Allston via Downtown and Cambridge (Kendall)
Allston to Chelsea via Downtown and Sullivan
Get rid of North Station. Most ideas about the Rail Link include three downtown stations. But you only need two. Where North Station is today is convenient to very little, and the half mile to its north is taken up by highway ramps and water. A better idea would be a station between Aquarium and Haymarket. It still allows for transfers to all subway lines, and there is very little that is less than a 10 minute walk from North Station but more than a 10 minute walk from Haymarket. It would save money, too. (Obviously, the existing Green/Orange line station would remain.)
Open new land to development. Much of the land near North and South Stations is taken up by trackage, and the Rail Link, obviating the need for these stations (a couple of tracks to use in emergencies and for trains like the Lake Shore Limited might make sense, at South Station especially, although these trains could operate to West Station and provide connections there instead), and this would be very valuable land. In addition, it would render Boston Engine Terminal obsolete as maintenance would be for electric vehicles, and if maintenance facilities were rebuilt on less valuable land (say, in Billerica or next to the Anderson/Woburn station). Based on what Northpoint just sold for, it would be worth maybe half a billion dollars in development rights. A lot of this money could be captured to help pay for the rail link itself.
Will the North South Rail Link happen any time soon? Probably not. But hopefully this will help people understand its potential (which is huge!) and what we're talking about when we talk about the NSRL.