This is the idea I thought the idea "worm train" [link] was going to be when I got there by a link from "Commuter train de-crowder" [link]. I searched for this and didn't find it, so I'm posting it.
You know how a chairlift at the ski hill works? The chairs are spaced out quite far apart on the cable while they're traveling, but they're condensed together at the stations (by disconnecting them from the cable) because they need to slow down to let people on and off, but they need to maintain the same numerical rate of chairs past any given point to avoid a pileup.
This does the same for trains. While traveling, the trains are spaced far enough apart that they can travel at a good speed without a significant risk of collision. Coming toward a station, they slow down and get closer together. At the station, there's a steady stream of trains, such that as one is leaving the platform the next one is already pulling up. As the trains leave the station, they accelerate and get farther apart for the journey to the next station. In this embodiment, the trains do come to a complete stop at the platform, like current trains do.
Now imagine that instead of trains of a few cars long, each train is only one car long. However, the platforms are still several cars long. The individual cars behave as described above, except that they don't come to a complete stop at the platform. Instead, they move along slowly, and getting on and off is facilitated by a travelator, as described in the idea "non-stopping train" [link]. They may temporarily link up with each other while moving along the platform, or just follow each other closely.
The above two embodiments could be facilitated by collision avoidance technologies such as radar-based adaptive cruise control from road vehicles, GNSS tracking, or maybe a track-conducted TDR method [link].
Now imagine that those cars are linked by an extensile tube with a substantially similar cross-sectional outline to the cars, such that they form one continuous vehicle that expands and contracts lengthwise in waves. These waves are stationary with respect to the surroundings (so that the peaks of compression stay aligned with the stations) but backward with respect to the forward-moving train (so that the peaks of compression stay aligned with the stations). The tube may use overlapping plates, and a mechanism similar to that of a Hoberman sphere, to expand and contract lengthwise between the cars as they get farther apart and closer together. This is what I imagined the idea "worm train" to be, based on its title and how it was described in the link to it from the idea "Commuter train de- crowder". This version is probably a lot less practical and useful than the previous two, but it would cut down on aerodynamic drag, possibly especially if the tube was sealed and air was passed in a controlled manner from in front of a given car to behind it, such that the tube-contained air between any two given stations remains the same air even as the train and its connecting tube move forward around it.
N/A [2019-11-30]-- notexactly, Dec 02 2019 worm train by [hippo]. Mentioned in idea body. The idea that I thought was going to be this one, but was not. It's actually about train propulsion (I think). [notexactly, Dec 02 2019] Commuter train de-crowder by [8th of 7]. Mentioned in idea body. The idea where [hippo] posted a link to the above-linked idea, whose description gave me the idea that that idea was this idea. [notexactly, Dec 02 2019] non-stopping train by [FireElf]. Mentioned in idea body. Basically the second version I described, without the specification that one train may pull up to the platform as the one ahead of it is still pulling away. [notexactly, Dec 02 2019] Train detection system by [Frankx]. Mentioned in idea body. Use of TDR through the train tracks to detect other trains on the same track and avoid colliding with them. [notexactly, Dec 02 2019] Discussion on how to board a fast-moving train Alternative_20Tube_...for_20dare_20devils [hippo, Dec 02 2019] Worm Train! https://youtu.be/87KYnPdQ0uU?t=855By coincidence, I saw this yesterday. [Loris, Dec 02 2019] condensation https://www.youtube...watch?v=CQGW46B6x_4con-den-sation! briliance [xenzag, Dec 02 2019] This is not a totally bad idea, but would it not be more effective to compress spacetime between the stations so that the trains can simply move with relatively low constant velocity ?-- 8th of 7, Dec 02 2019 Well this doesn't address the moist seats or inner window sweat at all!-- 2 fries shy of a happy meal, Dec 02 2019 This isn't the idea I thought it was going to be at all - I thought this would be something to condense, from the exhalations, coughs, sneezes, sweat and farts of a mass of tightly-packed commuters, water vapour that can be distilled, purified, automatically bottled, and sold via in-carriage vending machines.The idea, as written, though is good. As the carriages shuffle along, I think it should be possible for each carriage to come to a halt just for a second in the middle of the platform which would allow elderly or disabled passengers to board or get off. In that sense, this idea does have similarities with "worm train" but whereas the appeal of that idea was the peristaltic method of movement, with the train being a single, continuous body, urging itself forward in a series of rhythmic, almost fleshy impulses, this idea separates the train into small, separate cars. In each, the experience for the passenger, of slowing and speeding up in a station, is similar - this idea is arguably more practical and would cause fewer passenger deaths however.-- hippo, Dec 02 2019 Yes, there's a distinct downside.
// allow elderly or disabled passengers to board or get off.//
There's a trebuchet for that ...-- 8th of 7, Dec 02 2019 If there were two tracks in each direction (as is common on main lines) then you could have the "slow" train running as described in this idea. The "fast" train could then run on the inner track, 180° out of phase, so that it was running steadily alongside the slow train in the middle of the countryside, allowing people to move from the slow train to the fast train; the fast train would accelerate towards the station and zoom through without stopping, slowing down to synchronise with a slow train carriage half-way to the next station.-- pocmloc, Dec 02 2019 [pocmloc] I think that might be a separate (and very good) idea - to have express trains running permanently at 200mph on dedicated tracks. Then, other trains speed up to the speed of these trains and transfer passengers, and then slow down to stop at a nearby station to transfer passengers-- hippo, Dec 02 2019 //Now imagine that those cars are linked by an extensile tube with a substantially similar cross-sectional outline to the cars, such that they form one continuous vehicle that expands and contracts lengthwise in waves. [...] if the tube was sealed and air was passed in a controlled manner from in front of a given car to behind it, such that the tube-contained air between any two given stations remains the same air even as the train and its connecting tube move forward around it.//
If you're doing that, you could instead use the entire carriage-rear-plate : tube : carriage-front-plate assembly as a combustion chamber.-- Loris, Dec 02 2019 Or a giant accordion.-- MaxwellBuchanan, Dec 02 2019 Is there a difference?-- pocmloc, Dec 02 2019 Noone has ever been formally diagnosed with obsessive-compulsive variable-length train arson disorder, whereas there are many who crave the sight and sound of burning accordions.
Nor will we swerve from our great task until the last wisps of smoke have ascended to the skies.-- 8th of 7, Dec 02 2019 You know, I rather like accordions. I always think of them as being friendly and cheering, even if they are rather bulky. A friend of mine has two of them - they're great except that they tend to take up a lot of space on the sofa.-- MaxwellBuchanan, Dec 02 2019 No, hang on, now that I think of it they're St. Bernards.-- MaxwellBuchanan, Dec 02 2019 Easy mistake to make. Just squeeze them in and out- the difference in sound is quite distinctive. Also, it's possible to sit with a full-size accordion on your lap and still breathe.-- 8th of 7, Dec 02 2019 You have tried it then?-- pocmloc, Dec 02 2019 With a representative sample of one adult St. Bernard, yes.-- 8th of 7, Dec 02 2019 At the time we thought your pants were on fire.-- Loris, Dec 03 2019 random, halfbakery