Oh my. There’s an excellent interview with Jarrett Walker about mass transit and self-driving cars. While there’s a lot in there, he notes that geography is really crucial (boldface mine):

But we now have enough experience to know what we should have known all along, which is that transport, nevertheless, takes place in physical space and physical space obeys laws of geometry and physics and no technology is ever going to change geometry—never has, never will.

So, I think, we’ve seen, as with this attempt to somehow harness physical space through the power of apps, that there’s just a basic philosophical problem there, which is that transport is fundamentally a physical, spatial problem. It is not fundamentally a communications problem or to the extent that it was a communications problem, we’ve gone most of the way, I think, in taking that friction out of the system. And what Uber is discovering, I think, what a lot of these tech firms are discovering is that taking that friction out of the system did not transform the fundamental reality of space and the math of labour and so on, which have really been the facts that have determined what’s possible in passenger transport and will continue to determine those things.

In many cities, when there are events (e.g., concerts) or simply times many people want to be in a particular place, traffic grinds to a halt. And lest you think we’ll be able to pack more cars in a given area due to ‘smarter cars’, well, nope:

No, of course, the driverless car people will say, no, cars will fit closer together and they’ll be smaller and so we’ll fit more of them over the bridge but that’s a linear solution to an exponential problem. The other dimension of this problem that you must keep in mind is the problem of what we, in the business, call induced demand. And induced demand is the very simply idea that when you make something easier, people are more likely to do it and this is why, for example, when you widen a motorway, the traffic gets worse or it fills up to the same level of congestion that you had before. It’s because when you actually create new capacity, people use the capacity and you end up back in the same point….

If there’s a single concept that transport professionals almost all understand and almost nobody else understands, it’s this notion that the relationship between demand and usage is actually circular, the relationship between demand and capacity is circular. That is to say if/when we create more capacity, we trigger more demand. There’s a huge issue then because one of the things that Uber has done is very effectively induce demand for a whole bunch of new car trips in the city that weren’t happening before and this has had the effect, of course, of increasing congestion. The other thing they’ve done, of course, is draw people off of public transport, which is a great way to increase congestion. And so this is why it’s tricky and this is why in your example of a bridge, if you widened the bridge but lots of people want to cross it, you’ll end up with a wider bridge that’s exactly as congested as it is now.

There’s another issue Walker didn’t discuss regarding self-driving cars which is the issue of priority. While self-driving cars are typically portrayed as autonomous actors, for them to realize their full potential, there has to be some sort of coordination scheme. I don’t necessarily mean a top-down command-and-control center. But priorities will have to set to optimize traffic flow: certain roads might have to be slowed down in order to let other roads faster. Of course, there are other priority issues: do school buses or mass transit get faster trips? Emergency vehicles? What if some rich misanthrope wants to go faster? What if other people want to stick it to said misanthrope?

These are political and ethical issues, and can’t be solved with a killer app or brilliant piece of code. So even if these cars don’t routinely bump into things, there are some very hard problems to solve.