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Comment by black_puppydog | Hacker News Reader

It also shows an effect that the focus on high speed rail brings: rural areas are often very badly connected. Here in France they've even kept shutting down regional lines. That creates the train equivalent of "fly-over states": areas that you see from the train while going through, but that it would be impractical to go to.

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Has anyone considered the following? In a small town, you have a section of track running parallel to high speed rail. The track has a small and short "local" train (maybe just a couple of cars) that picks up passengers and accelerates to maybe 80 MPH, while the high-speed train slows to the same speed. The trains run next to each other for a couple of miles, some doors open between them, and people can step between the "local" train and the "long distance" train.

This lets the high-speed train serve a lot more places without losing much speed. Maybe the local train serves several towns in the area.

It has been considered and basically it’s not really reliable or practical or safe.

It was also planned for cargo (e.g. at the Megahub Lehrte) but didn't really pan out there either, even though ISO containers are much more predictable in their self-propelled movement than humans. At least all the material from that site now shows much automation, but it all happens at rest.

The problem is it's doable but if you do it, you might as well have a slow, regional railroad that goes between the stops of the fast international railroad. So a local/express situation, which is much simpler technology-wise.

Is there any writings on this? It sounds interesting.

My google fu is failing me but here are a few of the problems.

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Reliability

For a connection like this to work the trains have to meet, consistently, every hour or however frequently they run. This is pretty difficult, most rail networks are highly complex and delays cascade across a network. With station transfers this is okay, you can drop off anyone who needs to transfer to wait and let everyone else continue, but in this sort of moving transfer either people just totally miss their connection because it wasn't there, or the train loops around somehow and delays everyone else continuing on.

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Practicality

Let's say trains meet at 80 mph. Assuming you give people one minute to get their bags, walk to the door, take their seats in the other train (fairly aggressive for anyone who isn't a fit young adult) that means you spend 1.3 miles of distance traveling. That means 1.3 miles of parallel track where neither train can actually stop to serve local communities.

Station transfers in comparison are fairly compact (the length of a train) and they can actually also let people on and off from the surrounding areas with appropriate exits, whereas that's not possible with moving trains.

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Safety

We can't really guarantee two trains will move at the same speed parallel to each other. Trains are not automated to such a degree outside of self-contained metro networks, full automation is too complex to do in one shot and partial automation is still very complex and in its early days. Also whatever physical mechanism has to be tight enough to accommodate accessibility (wheelchairs can't go over large gaps) and reliable enough to work all the time; what happens if said mechanism breaks down while the trains are moving and conjoined?

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Finally there's the matter of actual need. If you need trains to not get slowed down, you can have some express services skip connecting to local regional services at all. It turns out demand for that kind of service is fairly limited; as an example, Amtrak has tried several times to introduce nonstop DC to NYC service, but it turns out that the additional passengers do not offset the loss of passengers from Baltimore, Wilmington and Philadelphia.

I've mused about a similar idea for California's high speed rail, which, should it ever be built, would be rendered impractically slow by frequent stops.

The idea is to drop cars without slowing down. These cars would have brakes, that's it. Before the station, drop the car, it slows enough to give safe time for switching, and cruises to a halt at the local station.

That's drop off, pickup is the slow train, which runs twice a day in each direction and assembles the carriage on the way.

Impractical for various reasons, sure. But what if.

The plan for California high speed rail was to replace plane flights and long distance car travel, not to have frequent stops (at least 40 miles/65 km between stops, sometimes longer). Only the major cities.

Yes, that was the plan. The raison d'être, even. But if it ever gets built, it will be obliged for political reasons to stop so often as to make it an unattractive alternative to flying from SF to LA or vice versa.

I could swear I've seen illustrations of such concepts. In the same theme as circular runways and having runways balanced across the tops of city skyscrapers.

The "moving platforms" concept seems to come up quite often, ala https://www.youtube.com/watch?v=MlhuHmVn4Ss

Except "flyover" states are not just rural areas. There are tons of big cities in non-coastal areas of the US. I don't think people who use the term are maliciously doing it, but it does diminish the lives of millions of people as unimportant and inconsequential compared to the "important" areas on the coasts

> Except "flyover" states are not just rural areas

Not just, no. But, looking at population density by states, you've got roughly:

(1) the coastal states way at the top (except Alaska, Oregon, and Maine), (2) non-coastal Mississippi River states, Oklahoma, Colorado, and Arizona, and Vermont in the middle (3) Everything else.

They are very different environments for things like passenger transport economics.

> There are tons of big cities in non-coastal areas of the US.

Define “big city”? There are three (out of 24 in the US) metropolitan areas with a population over 2.5 million where the principal city is located in a state without ocean, Gulf of Mexico, or Great Lakes coast; 0 out of 9 of your cutoff is 5 million.

Well, yes. New Yorkers and Californians see the rest of the country as useless, and most don't bother to learn that entire cities exist outside of their coastal regions.

It's also part of the current hyperpoliticalization we're seeing.

> New Yorkers and Californians see the rest of the country as useless,

I've known lots of both (more of the latter), none of whom believe anything like that.

I've knows lots of New Yorkers who think the middle of the country is just backwards uncivilized rednecks, since I'm from New York.

As a contrast Japan seems to have done a pretty good job of maintaining rail service in really rural areas.

This is the strong argument against high speed rail in the USA.

We don't even have anything close to regional rail, and highspeed rail would consume all public capital that would be used to improve regional rail systems.

Existing freight rails are so bad that passenger rail should get its own pairs of tracks in many cases (both to be higher speed and to serve the places people actually live, work and shop), and if you’re going to the expense of building new you may as well build it to support higher speeds.

> public capital that would be used to improve regional rail systems

could be used, but we all know thats not how it works ...

Commuter rail expansion and operations is the primary capital consumption area now, and there are more than a few such local / regional rail systems that could use several billion dollars each, on a continuing basis, for equipment, roadbed and station expansion.

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