Thanks to everyone commenting on the airport proposal! I got a couple pages of responses here, then no time to respond for a few days, but I'm back
It's not going to connect to NSRL 100 feet below ground. Your junction is north of North Station where the tracks are mid-ascent on a maximally steep 3% grade. You're going to have to go back DOWN...on a curve...to get underneath Charlestown. Assuming it's even feasible to shiv in a junction in the middle of a 3% grade, lest you have to send all of NSRL back into design at untold cost bloat. Yes...it will be a 15-20 MPH slog, for damn sure. You're not considering the third dimension at all with that drawing.
I see, I see. My bad. My drawing was off and I was throwing out NSRL specs from memory, which were wrong.
Ignoring the details of what I drew before, have the airport tunnel branch off just north of the underground North Station. There are a few hundred feet of level track there to do so. Like this:
That's deeper than I said before, closer to 150ft underground. The extra depth is no problem for a gentle ascent up to an airport station. A 0.5% grade on the curve and 1.5% grade on the straightaway brings the tracks up to surface level at central parking at Logan. Assuming the train platforms will be underground, those grades will be slightly less. That eliminates the vertical junctioning and slowdowns.
All that said...
Put it this way...if we're going to be chasing overrated things, shouldn't we be aiming to make them only slightly overrated like Levy says? In that case, the 4-minute longer trip on the existing Eastern Route tracks + a 3000 ft. small slice of SL3 surface ROW + a 2500 ft. under-Creek & highways tunneled segment is much much more slightly overrated than the extremely overrated $2B NSRL appendage with complex vertical junctioning that saves only 4 minutes (but probably not even that) from the same trip.
Yeah, sure y'all have convinced me. This and comments from
@TheRatmeister and
@ulrichomega all sound good. Going through Chelsea first looks a lot cheaper for a small time impact.
One kind of (not really) problem with that route is all the grade crossings through Chelsea. It seems like there would need to be grade separations there even for existing Regional Rail planed frequencies, let alone adding in trains to the airport. Does anyone know what the plans there might be?
It would probably have to be in the same ridership stratosphere as today's North Station to possibly make fiscal sense, and there's no possible way to extrapolate that much Logan potential from the current middling transit numbers the airport does from this whole region with its not-at-all-bad transit access. The potential is an order of magnitude shy of fiscal sanity.
If the comparison is North Station, then an airport regional rail station would need to take what, like 15-20% modeshare? (There's 85k going to the airport daily, and a mostly different 85k leaving the airport, so it's a different pattern compared to normal commuters into North Station, and I'm just trying to pick rough, round numbers for the sake of a crazy transit pitch). That's not an outlandish expectation for something like I'm proposing (or the cheaper route along the Eastern Route). Those are the kinds of numbers you could expect from a convenient, frequent train that directly goes to multiple downtown stops around hotel clusters.
20% of people take the Canada Line to and from Vancouver's airport. The Heathrow Express was overpriced for sure, but the Piccadilly line apparently carries
in the 20s% of people to and from Heathrow (sorry I can't find the exact number). I've seen DCA has the highest transit modeshare of US airports(13% I think, but I've lost my source), mainly because of the subway connections. Those connections are great for getting downtown, but it reaches that modeshare without even being very good at connecting to the suburbs. The airport link I'm proposing is like if DCA was also connected to a half dozen regional rail lines radiating out in the Virginia and Maryland suburbs, as far as Baltimore. In that case, the transit share would obviously be higher.
And there is good reason to think this line to Logan would be among those high performing examples. This would go directly to several major hubs of business and hotels in the city. It also connects lots of the suburbs where local traffic is disproportionately originating from. It offers all kinds of one-seat-rides, which boosts ridership, especially for people carrying luggage. Lots more trips are possible with cross platform transfers. The train station can be right at the airport, without the need for extra connections on busses or people movers, right where we could automatically direct people coming out of arrivals. So in a very hand-wavy way, yes, I think this airport link would be the kind that pulls in a double digit modeshare. And I think that would put it in the ballpark of North Station ridership, if that's the cutoff you want to pick. It would be at least close enough that I don't think it can be dismissed out of hand.
As for trying to extrapolate from current public transit numbers, that doesn't really make sense to me. The Blue and Silver lines to the airport are not great. The Blue Line is the shortest, least connected rapid transit line, and still requires a transfer to a bus to get to the terminals. The Silver Line is a bus that gets stuck in traffic, regularly taking a half hour to get to or from the airport. Personally, I
stubbornly take public transit, but even I've started taking rideshare on the odd occasions I'm going to the airport. Or getting someone to pick me up. So it's not surprising to me that those services get middling transit numbers. But I don't know what they can tell us about possible ridership on what I'm proposing, which would be maybe one of the fastest and best connected airport links in the world.
Are you actually expecting that the southside suburbs alone are going to ride to Logan daily at a North Station-ridership level? And if so, where have all those people been hiding all these decades?
They've been driving to the airport.
RE: Terminal station placement. I think it's a given for this project that you need to be tunnelling under the terminal buildings themselves, otherwise none of this works. That said, could we share terminals for E/C and A/B? I make this out to be ~800 ft radius between the two terminal stations, with the curve out of Airport being worse, but I think that one's much more fudgeable.
That's interesting. Thanks to you and
@Riverside for all your other pictures of measurements on other airports. Station location(s) definitely isn't something I've found a perfect solution for. I still think the best would be a single central station, looking something like this: