Comment by lorenzhs | Hacker News Reader

Comment by lorenzhs | Hacker News Reader

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Driverless trains have been here for a while. They're great. With platform-edge doors, nobody can fall or jump onto the track, not to mention that they increase brake cooling efficiency and decrease air resistance (less air to push).

But of course you weren't talking about trains.

I see this sentiment a lot on HN that self driving cars are going to fix everyone's transportation woes, but I'm not convinced that they will. For example, they're never going to be particularly efficient at really high speeds, due to tyre wear (due to heat) and air resistance (which can be reduced by driving in a convoy, but not enough). Rail (or maybe hyperloop, who knows) will still be much more efficient for high-speed travel, not to mention much faster. So maybe the cars will all be going 40% faster on highways than nowadays, which is nice, but still only half of what rail can do, and even less for hyperloops.

I don't buy the "it's gonna fix everyone's commute", either, because at the same time it's supposed to fix parking. So now you have loads of cars driving out of the city to park at the same time as you've got just as many driving into it. Sure, vehicle-to-vehicle communication and superhuman reaction times will allow for increased density on roads, but is it enough to offset the increase in traffic? And is the increase in miles driven and resulting road maintenance cost factored into the cost calculations?

Damn right I want cars to drive themselves, and it's going to be fantastic. But I don't think autonomous cars are the panacea that many seem to see in them.

I agree with your scepticism about solving the commute traffic with a self-driving silver bullet. The research for traffic flow [1] says that, with human driven cars, a slice of a 4m wide lane will pass about 1000 people/hr in cars, about 7000 people on foot or bicycle, and about 10,000 people by bus.

That means that to get competitive flow with buses, self-driving cars need to deliver a tenfold improvement in flow. Since in traffic cars are quite tightly packed already, you probably can't get much from putting them closer together, so even if self-driving magic gives you two doublings of flow on its own you still need to more than double the speed limit to compete. I can imagine this working only on roads dedicated to self-driving vehicles, with no pedestrian crossings, so now self-driving cars benefits only materialise if they eat up a chunk of the public space.

You might get a bit of improvement from vehicle sharing as well, but it seems like a really complicated way to attack a problem that already has an OK low-tech answer, at least in high density areas.

Where I live the census says that about half the commute journeys in the area are less than a few miles, for which cars of any sort seem ridiculous to me, for the able bodied. For those who aren't able bodied or have a long journey all the able bodied car users on short trips are using up a scarce resource that they need!

Throw in the health benefits of active transport, and the health cost of particulate emissions (still a problem with electric cars, since a decent chunk comes off tyres and brakes) and it looks like a wash to me. Then again I am one of those awful bike people, so maybe I miss the point.

[1] Litman 2017, Brun & Vuchic 1995 etc.

Outside of NYC, in the U.S. public transit in my experience takes two or three times as long to get you where you're going. Until the typical experience gets better or people get poorer, the resource efficiency won't matter.

The common American is getting poorer, but just like junk food and lack of exercise, people still drive. Other modes of transit may be much safer and healthier, but unless the common person is encouraged (whether that be with incentives to not drive, or tolls for driving) quite a few people will still drive.

There are a number of US cities that get most workers into the urban core besides NYC despite poor to middling infrastructure at best, but driving infrastructure dwarfs everything else, bike lanes are added only to diet roads usually (resulting in shitty lanes), and most areas see 60% to 70% of their land tied up in (mostly empty) parking, which is a disaster for every mode of transport.

I guess part of the issue here is that cars are a kind of coordination problem - if nobody else is using a car on the roads, cars are quite a good choice. They are fast and easy, and go where you want.

However, each person who uses a car creates some external costs (a high traffic factor / unit of person-flow) which are borne by all the other road users. Once people choosing the "defect" strategy (cars) have enough numbers, the "cooperate" strategy (not cars) gets broken for other solutions that use the road network, so the system fails to a bad equilibrium if there are enough defectors in the population.

Congestion pricing would solve that, and go nicely with robocars too.

(I'm not a fan of cars; I don't drive one myself. But I don't expect people to accept any less convenient and flexible solution.)

Not sure what rail services are like where you live, but in the UK it's about 50/50 whether it is faster to travel between major cities by car or by train. Trains can go faster but this is often counterbalanced by needing to slow down to come to a stop, etc. There will always be places that can't be reached with public transport and even in cities like Paris renowned for their public transport it is often necessary to change several times as part of a journey.

Many light rail services e.g. BART and the London Underground are completely crazy at rush hour and there are many obstacles to increasing frequency. A big challenge of self driving trains is ensuring they are able to stop in time if an obstacle is present, and this relies on fairly similar technology to that of driverless cars. Self driving cars would reduce traffic because they would reduce accidents and allow cars to sort themselves into slots automatically rather than waiting at traffic lights.

You have a good point about rush hour traffic being increased by cars driving outside the city to park, although cars could park more efficiently in city centres if multi-storey car parks didn't need to allocate space for humans.

I'm confident in saying there's zero chance that self-driving cars, on their own, could replace the London Underground. Zero.

The Underground (and commuter rail that feeds into it) carries a vast number of people every day. There's just not enough road space to get that many cars in and out, even if they were 2x or 4x more efficient.

If you want to fix the Underground (although it works fairly well so it's not clear why drastic changes are needed) you need to start thinking about buses and bicycles, staggering working times to avoid rush hours, moving jobs outside the city so people don't have to commute in at all, that sort of thing. None of those actually needs AI.

Self-driving cars (and especially self-driving buses and minibuses) can certainly be part of the solution, but they're not the solution.

Where a train can move 20k+ people an hour in each direction, a standard road moves around 1k. Self driving cars will only make sense as chauffeur replacements for Uber, Lyft and Taxis, as even with a tripling in capacity, you'd still be wholly uncompetitive with rail. Nevermind the inefficiencies of enlarging roadways :P

> If you want to fix the Underground (although it works fairly well so it's not clear why drastic changes are needed)

The population of London continues to increase. Central, Northern, Jubilee lines are often difficult to get on during rush hours, and even harder to stay on. And that's in the winter, summer time's a whole other ball game...

Self driving cars are certainly not the solution, but that's not to say there's not plenty that needs fixing on the London Underground.

https://www.youtube.com/watch?v=FOF_XIylzS8 still rings true, albeit with less BK these days than before.

I don’t think I’ve ever heard someone claim driverless cars will fix everything

Mass transit specifically trains have serious problems I don’t think there are solutions for. The first is that they make centralized points of failure. Broken trains can bring a whole city to a halt. The second is they are the perfect germ delivery system.

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