Here's my take on how the math for express trains works (doesn't work in this case).
An express train is faster because it doesn't stop. It doesn't go any faster on the rails themselves. The time a train spends on a stop is three things; first time lost because the train is decelerating (rather than going through at top speed), then a dwell time while passengers get on and off, then acceleration time to get back to the top speed. The acceleration and deceleration of an Urbos 100 is 1.32 m/s^2 (symmetrical) per Wikipedia. That means that the added time for accelerating and decelerating are each in the range of 7.3 to 8.3 seconds (depending on top speed - those are for 70 and 80 km/h top speeds). So that's 16-17 seconds. Then there's the dwell time, which is in the 15-30 second range. So the total time is 30-45 seconds saved per stop.
Let's say we're skipping four stops; South Hill, Lynnwood, Highfield and 26th Ave. South Hill is currently nothing much, Lynnwood will never be much. Highfield and 26th Ave are lower density industrial parks. Note that eventually South Hill is intended to develop at a fairly high density, and I wouldn't be surprised if it was the central hub for bus service to the SE industrial area (perhaps the Max Teal is routed through here), so maybe skipping it doesn't make sense. But in any case, there's 4 stops skipped, let's say 30 seconds per stop. Here's what that looks like from Shepard (I'm assuming 30 minutes to the downtown for simplicity; the Green Line website quotes 37 minutes to 16th Ave, and 10 minute frequency).
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What is clear from this is that the express doesn't save you all that much time. No matter when you arrive at Shepard station, you should take the next train, express or local. Unless you want to go to the four skipped stops (and there are hundreds of jobs around Highfield and 26th Ave in particular) - in which case, you have to wait an extra 10 minutes if the next train is local. Similar if you're at one of the skipped stops; you have a train only every 20 minutes, all to save Shepardites 2 lousy minutes going to downtown.
Note also that the express train never catches up with the local train, so no passing infrastructure needs to be built. A service pattern like this could be run on the existing lines today, if we wanted to cut transit service for a lot of people to save a couple of minutes for a few.
Here's the extreme example; let's assume that the train runs twice as frequently and skips twice as many stops - the four above as well as Quarry Park, Ogden, Inglewood/Ramsay, and the east Beltline stop at 4th St. Douglas Glen is the major park and ride lot, as well as the main bus terminal, as far as I know. But if you want to service QP, you could skip it instead.
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Only here, having made a lot of really strong assumptions, do we have an express train that gets you there faster. But not by a lot; I caught a bus this morning, and given the choice of getting on board right away or waiting more 5 minutes outside and getting to my destination 1 minute faster, I wouldn't pick the express option. And that's assuming I want to get downtown, not to Quarry Park or any of the industrial areas, and that I'm coming from Shepard, not Ogden or Ramsay -- in any of these cases, I can't take the express train and my service is just straight worse.
The secret as to why only New York has express trains isn't because nobody else is smart enough (or even densely built enough), it's that New York made the mistake in the first place of building the local trains. A forgivable mistake - first movers always make them. But express vs. local works there, where to take an example the 1 and 2 lines run parallel from 96th Ave to Chambers. The 1 stops 18 times, and the 2 only 6 times on the same segment; the express train takes 23 instead of 16 minutes; 35 seconds less per stop. But they also run incredibly frequently - 4 and 5 minute headways all day. So you get something more like this:
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where it always makes sense to take the express if you're going somewhere it serves. But the thing is that it's 17 km from Shepard to the Beltline, with 9 stops in between, a stop every 1.8 km. And it's 9.5 km from 96th to Chambers, on the express 2 there are 4 stops in between, one every 2.4 km. It's not that we should trying to add express trains, we already are. It's the local service - (16 stops from 96th to Chambers, a stop every 500m) - that we're not building.
PS: The bypass you show isn't regularly used by the Hudson Bergen light rail, from what I can find out. They actually do operate skip-stop express service (the "Bayonne Flyer") in the rush hour on a different line, which I'd bet money is because New Yorkers (and NJers who think they're New Yorkers) have a positive image of express service, and it's really a marketing ploy. The express trains don't pass the locals, so no bypass tracks are needed, and they only take 4 minutes less end to end.
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