Comment by seabass-labrax
7 days ago
I feel as if the time spent by each passenger walking to the right boarding area could easily surpass the dwell time of an extra stop or two.
Consider a metro system with trains 70 m long. With 10 m of space between the two boarding areas, that means the length between both sides of the station is 150 m. If the entrance to the platform is in the center, the walk to the middle of each boarding area is 45 m, taking about 30 seconds. If the entrance is at the end, that becomes 35 m or 115 m (taking about 20 to 90 seconds to walk). I think those figures are comparable to the dwell time of a typical metro system.
I do think it's a very interesting idea though! I think it'd work better for longer trains over longer distances, where the time spent accelerating and braking is often greater, but unfortunately few places are even considering anything shorter than 15 minute headways for such rail services.
Admittedly my calculations did not take walking-on-platform time into account, but what I have been assuming (based on figures I've looked up) is that each stop adds about 60 seconds to the journey time (30 seconds for dwell + 15 on either end for getting up to / down from cruise speed). I've also been assuming that the inter-station no-slowing-down time is 2 min.
So in a 2-of-5 stopping pattern you'd save 3 min every 5 stops, but depending on when arrive at the station you will sometimes get unlucky and just miss your train, in which case you'll have to wait an additional interval than you normally would for the next one (costing you 3 min). So for very short trips (under 3 stops) it actually makes travel time a bit worse since there's very few stops you can skip over in such cases. But for more median trips there is a saving, and for the longer trips it saves well into 2-digit minutes.
In your example I think in the case with the entrance at the middle of the platform there wouldn't be any real effect, because splitting the platform also in the middle doesn't marginally change how quickly you can get to the nearest open door on the train you want. There's no real need to get to the center of either boarding area. In the case of platform at the end of the station, I can accept that adds about 40 m of walking distance that wasn't there before (at least for some people), and that translates into an extra 20ish seconds. Less than that if you do the rational thing of walking briskly when you see you're about to miss your train.
So you're right that the platform split adds some time which isn't completely negligible, and depending on what fraction of the next n stops you want to skip it comes at a penalty of longer wait times for the correct train, but both of these are fixed upfront costs whereas the dividend accrues linearly the longer your on the train.