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Comment by cyclingfarther | Hacker News Reader

You can always gain efficiency by giving up safety.

Just look up peloton crashes. Or imagine cars driving like that.

there are automated peloton machines that do synchronized braking, cooperative load and force distribution, etc. and when on a specialized roadway there is very little risk of disruption or crash.

i think they're called trains

I get that this is sarcasm, but one of my idle day dreams is a safe, simple, mostly analog system that does exactly this between a set of moving train cars and the last car on the rear (as a transitional state, the rear car eventually catches up and mechanically couples). I call it the reverse slip carriage. If it can be done, it would keep all the advantages of trains while also totally revolutionising possible service patterns. You could (for example) have a train where every carriage slips-off to make its own subset of limited stops and then slip-joins the next train to pass by. Passengers pick where to wait on the platform based on their destination, and there's always an express carriage to where you want to go. Another neat service trick this system could do is to have an 8 car subway which runs every 5 min that splits itself into 4 different 2-car light rail services every 5 min (rather than 4 subway branches with an 8 car train every 20 min (looking at Rockaway beach A train)). The ability to split and rejoin trains on the fly without stopping or spending time on coupling procedures is simple yet it would be profoundly game changing.

My current vision for the system basically amounts to electrically coupling the motors of the carriages such that any attempt to accelerate / decelerate one carriage transfers energy via induced voltage which accelerates / decelerates the other carriages by exactly the right amount. It's like an electrical version of how all the cable cars are holding on to the same rope. No computer, no glitches, entirely dumb components.

What about the train drivers? They seem to still be necessary.

Barely.

In principle, railways would not be difficult to automate. But it hasn't happened at scale yet because industry regulations require that trains be manned, and railroad unions would strenuously object to any suggestion that this be changed (since it would likely put a lot of conductors out of their jobs).

Some public transport systems have omitted the driver, but they still need a human attendant for safety to make sure that no passenger is stuck in the doors before departure (and other exceptions to smooth operation). One that I've ridden is Docklands Light Railway (DLR) in London.

Others have pointed out driverless metro is already a thing in some places (from memory Singapore MTR, Sydney Metro, Docklands light rail in London, airtrain at JFK airport (NYC), Vancouver SkyTrain). But let's say for regulatory reasons you need a driver. So the way this would work is the electric motors in both the driver operated train and the slip carriage are electrically coupled via the rails. Technically the one driver is operating two trains with a single controller, but the circuitry is set up in a way that the second the slip carriage is always responding to the controls identically to the main carriage +a few m/s until it gets close enough for mechanical coupling. So the driver has no mental overhead in managing the secondary train sets. From a transfer of momentum perspective, his train behaves as if the slip carriages are already mechanically part of his train.

For the sake of example, I'll focus on my second use case. A mainline heavy rail that branches into multiple light rail at the same service frequency. In this case, the carriages split off from an 8 car set into two car sets and coast to a stop at designated branch station (like old fashion slip carriages from the late 1800s). At those stations new drivers board to take over light-rail style operation. When the drivers complete the route they step off the train at which point the automatic reverse slip carriage system rejoins them into an 8 car train (one driver stays on to become the lead carriage). The drivers that stepped off then cross the platform to take over control of the next train to split itself.

A strange but doable logistic coreography that lets metro lines branch more without intolerable service frequency.

I'd say it depends on the group, if you have a group of riders that know each other and have ridden in packs before then the risk of issues are slim. Essentially just stuff that probably would have given you trouble riding alone anyway. The risk starts when you either have a race going on or you have riders that are inexperienced and don't know the customs/procedures.

Yep. It’s definitely something you want to train for.

It’s one of the main reasons to join a bike club.

A good group will call out obstacles in the road and say when the are going to slow down. They’ll have set procedures to move the group round when the riders at the front get tired.

The experience of being pulled along faster than you could ride on your own is a truely joyous experience! :D

> The experience of being pulled along faster than you could ride on your own is a truely joyous experience!

It truly is! As a kid we used to hide behind the double decker busses on our mountain bikes at the stop and accelerate with it when it got going again. We’d be riding only a few feet from the rear of the bus and it’d pull us up the big hill home so fast. The bus driver used to get really annoyed and eventually snitched to the school so we had an assembly about it !

boys are stupid!

I’d never have the balls to do that now!

Haha! I remember latching onto school buses and other large vehicles at stoplights when I was younger. Stay close enough, and you could get sucked along at incredible speeds. It was interesting how some drivers would get super-pissed, while others would think "hey, that's awesome!" and help you stay attached.

Riding in a pack is a whole different experience, though. You have to be hyper-aware and -predictable in your lines, but the feeling of cruising along at over 20 MPH on a flat, aided only by your fellow cyclists, is something special.

When motor vehicles do that, it's called a convoy.

When motor vehicles do that, it’s called Talladega.

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