[ Question ]

Will autonomous cars be more economical/efficient as shared urban transit than busses or trains, and by how much? What's some good research on this?

by MakoYass 2mo31st Jul 201910 comments

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There's reason to think they would be. When people get into a shared public transit vehicle, usually, they're not all going to the same place. The vehicle has to take an indirect route, it has to start and stop many times along the way to let people on and off. A person will often have to transfer between multiple lines along the way and that will often involve a bit of waiting. There are usually many routes that have very low utilisation rates- carriages will be mostly empty most of the time, in part due to the fact that you can't deploy half of a bus for low-use routes, in part due to the rigidity of the route scheduling.

Small self-driving vehicles, instead, can take a person straight where they need to go. The vehicle can then pick up someone else nearby and take them straight where they need to go, and so on, all day. They'll also benefit from economy of scale of production, if more units are produced, the cheaper they individually become, smaller units, then, can be cheaper.

That's the vision I have in my head, anyway.

The main potential issue that I can see is commuting patterns. If a lot of people are going in the same direction at the same time, batching their trips together with larger densely packed shared vehicles might make sense.

But I'm not sure that's a legitimate way for cities to be. With affordable inner-city housing, mixed-use planning, this commuting pattern wouldn't pop up - people would be taking short trips in all different directions even during peak commuting times.

(Although I cannot personally understand why) A lot of people seem to like living in suburbs, and conventionally planned cities have land pricing issues that make living in them prohibitively expensive for most ordinary people who work in them (I will discuss a potential solution to this in a later post). These ideal mixed use cities that I am mentally situated in, might not exist, and might not come to exist before autonomous vehicles start to compete with existing public transit.

So I'd like to know what relationship suburb size has to the commuting pattern problem - how large can the suburbs get before fixed-route busses become more efficient? (and also, are they really better, even with large suburbs? Is there that much route agreement in any city?)

Visions of self-driving cars currently look like variants of the cars we have, improved for not needing to have a driver's seat and forward visibility, often you'll see 8-seaters that're expected to be shared to some extent. I think that might be unrealistic, if it is, we need to see more analysis of single-occupant cars like the toyota i-road. Aside from using fewer materials and using less energy during acceleration (they're lighter)[1], they'd also have the advantage of being able to to drive two to a lane, reducing congestion.

If we can answer these questions well, I think we will be much better informed about the future of urban transit than we are now.

[1]: although, regenerative braking is a thing. I'm not sure there's really an upper limit on how efficient that can be made, so maybe weight isn't so much of an issue.

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3 Answers

I remember thinking through the potential evolution of autonomous transportation* some 10 years ago, and, barring the protectionist forces winning out and enshrining the "right to drive" in law, like the "right to bear arms", it's pretty clear where the transportation is going.

1. One- or two-person electric commute vehicles dominating city traffic, eventually leading to the whole swaths of urban areas being closed to human drivers, which would be deemed unsafe. Those areas will then expand outwards and merge, eventually spreading into the suburbs, and at some point major highways, first with HOV lanes, then taking over the rest lane-by-lane. Owning a car will become very expensive, and a human-driven car prohibitively so.

2. The huge parking lots will disappear, since uber-like electric commuters will be in use much more often and can be stored efficiently in much smaller spaces during off-peak times.

3. Everything will be routinely recorded, whether outside of the vehicle or inside it, limiting the type of activities one can indulge in while getting to the destination. Vandalism will virtually disappear, as well. Ride sharing will complete strangers will be as safe as walking along them on a busy street somewhere in central London.

4. Once there are no more human drivers, in the autonomous-only areas the vehicles themselves will be able to communicate and coordinate, and soon will be required to do so, forming a driving grid. Any vehicle not complying with the grid inclusion rules will not be allowed in, or forced to stop and get towed outside. Yes, the grid will eventually take control from the single vehicles.

5. Once that happens, the traffic lights will be largely obsolete. There will be pedestrian crossings, with the Walk/Stop signs, but no usual traffic lights, since there will be no human drivers to look at them.

6. The current alternating pattern of driving through the intersection will change: without pedestrian crossings cars will simply zoom in all directions, their movement perfectly choreographed by the grid. With pedestrian crossings there will be breaks for humans to cross on foot in all directions at once. Odds are, many crossings will be replaced with walkways above or below ground.

7. Congestion will be greatly reduced due to coordination. Worst case you'd have to wait to get your ride, as the grid will limit the number of vehicles to keep the system at peak efficiency. Traffic jams will be extremely rare, since most current causes of it will be eliminated, such as broken down cars, accidents, high volume traffic, power outages, road work (the grid will shape the traffic around any roadwork in progress).

8. The city architecture will change to accommodate the new transportation realities: there will be much less road space needed, so some of the wide busy streets will be repurposed for parks, living spaces, etc.

This is as much as I recall offhand, but there is definitely more.

Now, to answer your question, the costs will eventually go down orders of magnitude compared to the existing means of transportation. Which does not mean that price will go down nearly as much, as everything will be heavily taxed, like train and plane tickets now.

Edit: I expect this will happen first in places with high penetration of autonomous vehicles. Places like, say, Oslo. Also in the countries where the government can exert some pressure and ensure compliance and coordination, like, say, in China and maybe Japan. The US will be one of the last ones, and the most expensive ones, as is customary with most technological innovations lately.

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* The language will evolve accordingly:

  • "self-driving car" will be a name for DIY driving, the opposite of what it is now.
  • self-driving will be reserved for antique car enthusiasts, who would tow their cars to a "driving range" and show off their skills in this ancient activity, sort of like horseback riding is now.


In the short-medium term (next 30 years, say), change is going to be gradual. It will take a LONG time to overcome all the edge cases of current driver, traveler, and pedestrian expectations. We'll see more ride-share and semi-autonomous, and portions of the ride-share will become autonomous, but not a lot of end-to-end differences.

I haven't seen much study of the demand side of things - what is the actual price/time/convenience elasticity of common travel desires. I know that commute times stay fairly constant - people move further out when roads improve. I don't see why that will change - people will take more distance (and cheaper/roomier housing) over less time/resources for their commute. I do strongly expect that people will simply travel longer and more often as it gets cheaper/easier to do so.

Rail is here to stay, as it combines actual efficiency of resources with the populist demand for central provisioning and subsidies. Busses tick the same boxes (though less convincingly), and probably stay for the same reason.

@makoyass I think you would be interested in The End of Traffic and the Future of Access . I haven't read it, though I have read some of Levinson's other work; it's a bit on the dry-and-wonkish side, but I expect you would prefer that to "rabid conflict-theorist", and it's covering the right sort of ground.