notes on self-driving cars

A relaxing trip to work (courtesy wikimedia)
A relaxing trip to work (courtesy wikimedia)

Short post here. I notice people are writing about self-driving cars a lot. There is a lot of excitement out there about our driverless future.

I have a few thoughts, to expand on at a later day:


Apparently a lot of economic work on driving suggests that the a major externality of driving is from congestion. Simply, your being on the road slows down other people’s trips and causes them to burn more gas. It’s an externality because it is a cost of driving that you cause but don’t pay.

Now, people are projecting that a future society of driverless cars will make driving cheaper by 1) eliminating drivers (duh) and 2) getting more utilization out of cars. That is, mostly, our cars sit in parking spaces, but in a driverless world, people might not own cars so much anymore, but rent them by the trip. Such cars would be much better utilized and, in theory, cheaper on a per-trip basis.

So, if I understand my micro econ at all, people will use cars more because they’ll be cheaper. All else equal, that should increase congestion, since in our model, congestion is an externality. Et voila, a bad outcome.


But, you say, driverless cars will operate more efficiently, and make more efficient use of the roadways, and so they generate less congestion than stupid, lazy, dangerous, unpredictable human drivers. This may be so, but I will caution with a couple of ideas. First, how much less congestion will a driverless trip cause than a user-operated one? 75% as much? Half? Is this enough to offset the effect mentioned above? Maybe.

But there is something else that concerns me: the difference between soft- and hard-limits.

Congestion as we experience it today, seems to come on gradually as traffic approaches certain limits. You’ve got cars on the freeway, you add cars, things get slower. Eventually, things somewhat suddenly get a lot slower, but even then it’s certain times of the day, in certain weather, etc.

Now enter a driverless cars that utilize capacity much more effectively. Huzzah! More cars on the road getting where they want, faster. What worries me is that was is really happening is not that the limits are raised, but that we are operating the system much close to existing, real limits. Furthermore, now that automation is sucking out all the marrow from the road bone — the limits become hard walls, not gradual at all.

So, imagine traffic is flowing smoothly until a malfunction causes an accident, or a tire blows out, or there is a foreign object in the road — and suddenly the driverless cars sense the problem, resulting in a full-scale insta-jam, perhaps of epic proportions, in theory, locking up an entire city nearly instantaneously. Everyone is safely stopped, but stuck.

And even scarier than that is the notion that the programmers did not anticipate such a problem, and the car software is not smart enough to untangle it. Human drivers, for example, might, in an unusual situation, use shoulders or make illegal u-turns in order to extricate themselves from a serious problem. That’d be unacceptable in a normal situation, but perhaps the right move in an abnormal one. Have you ever had a cop the scene of an accident wave at you to do something weird? I have.

Will self-driving cars be able to improvise? This is an AI problem well beyond that of “merely” driving.”


Speaking of capacity and efficiency, I’ll be very interested to see how we make trade-offs of these versus safety. I do not think technology will make these trade-offs go away at all. Moving faster, closer will still be more dangerous than going slowly far apart. And these are the essential ingredients in better road capacity utilization.

What will be different will be how and when such decisions are made. In humans, the decision is made implicitly by the driver moment by moment. It depends on training, disposition, weather, light, fatigue, even mood. You might start out a trip cautiously and drive more recklessly later, like when you’re trying to eat fast food in your car. The track record for humans is rather poor, so I suspect  that driverless cars will do much better overall.

But someone will still have to decide what is the right balance of safety and efficiency, and it might be taken out of the hands of passengers. This could go different ways. In a liability-driven culture me way end up with a system that is safer but maybe less efficient than what we have now. (call it “little old lady mode”) or we could end up with decisions by others forcing us to take on more risk than we’d prefer if we want to use the road system.


I recently read in the June IEEE Spectrum (no link, print version only) that some people are suggesting that driverless cars will be a good justification for the dismantlement of public transit. Wow, that is a bad idea of epic proportions. If, in the first half of the 21st century, the world not only continues to embrace car culture, but  doubles down  to the exclusion of other means of mobility, I’m going to be ill.


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That was a bit more than I had intended to write. Anyway, one other thought is that driverless cars may be farther off than we thought. In a recent talk, Chris Urmson, the director of the Google car project explains that the driverless cars of our imaginations — the fully autonomous, all conditions, all mission cars — may be 30 years off or more. What will come sooner are a succession of technologies that will reduce driver workload.

So, I suspect we’ll have plenty of time to think about this. Moreover, the nearly 7% of our workforce that works in transportation will have some time to plan.


8 thoughts on “notes on self-driving cars”

  1. The NY Times thinks that the first driverless vehicles will be long haul trucks. Labor costs, you see.

    And even though an individual who drives does not bear all the costs of the resulting congestion (so yes, there are external costs), some of the cost is internalized not as dollars but as time. This seems to be one of the things that has driven the framing of the problem: not as “how do we get people from home to work to kid’s soccer game to supermarket?” but instead as “how do I not waste my time piloting this car down 101 from The City to Mountain View?” That is, if the cost of congestion is internalized as “wasted time” then the solution is to allow you to read or code or watch a movie while your car drives you to work. And even leaving aside for the moment your worst-case scenario of a catastrophic failure (which is pretty easy to imagine–a few weeks ago I witnessed a car fire on the approach to the bridge, and people, quite calmly, managed to squeeze about three lanes of traffic at a safe distance around the obstacle), what would keep people from deciding that they needed their own self driving driving car rather than using what amounts to a self driving taxi to get them to their destination? I am not sure that paying as you go (instead of at the car dealer up front) would necessarily reduce demand for automobile trips. Then again, the only place I have ever driven a car to work is Kenosha. It just seems to me that the problem with the auto is the footprint of the auto itself. Heck, it is why I ride a bike to campus even though I own a car and have a job that pays me enough to let me purchase a parking permit–with the tradeoff between the cost of the right to park, the distance of the cheaper lots, etc., I am better off with my two wheels and my free bike parking. As long as I don’t get clobbered by an automobile.

    1. You bring up interesting points. It’s probably worth noting that the people farthest along on the self-driving car are folks who ride a double-decker wifi-equipped bus to and from work daily.

      People with extra money will always pay to own. If most people do that, I guess the congestion situation is no worse than driving, except for the potential avoidance of parking by letting the car orbit, which could be much worse.

      But the one thing about driverless cars that I see as at least plausible, is that people will indeed choose not to own them, particularly if “renting” is cheaper. Aren’t things trending that way already, at least for urban dense places?

      Some of the problems of driving cars can be solved by smart policy. For example, we probably will probably ultimately have to tax vehicle-miles rather than gas, because cars are already using much less of the latter, and that trend will continue as our needs to maintain and perhaps even expand our infrastructure go up. Furthermore, we may want to consider taxing “empty vehicle miles” as a way to disincent driverless use of the roads-in-lieu-of-parking. And if you don’t like taxes, you could make it incentives instead, yadda.

      Perhaps this is all a very long-winded way of saying that cheap, low-impact mobility for all remains a complex problem and that driverless cars are mostly orthogonal to solving that problem; the driverless car solves a different, less important problem.

      1. Hear hear. While I agree that there may be an increasing proportion of people in cities who are fine with renting the use of a car, lots of people may be willing to pay extra for the convenience of having their own. I could use a car share, but I also like to think that if I want to pop out my door on Saturday at 7 a.m. and drive to Pt. Reyes I can do it without having a reservation and without having to wait. Since automobiles are the ultimate convenience, probably a substantial proportion of people in well-off urban areas will behave similarly.

        You can tell I am grading. Does anyone else frequent this blog?

  2. Plus–if they are already riding on a bus with wi-fi, why do they want self-driving cars? Merely for the privacy?

  3. I guess Margaret visits too. Maybe time for some optimization, get some of those transit/energy/data policy wonks in the mix.

  4. If self-driving cars handle more passenger trips per day (an owned vehicle dropping off multiple family members, say, or an Uber fleet car driving passengers all day long), they can in principle replace underutilized cars that spend most of their time parked. But that doesn’t work so well at rush hour, when many people need to be in transit at the same time, even if a self-driving car rounds up carpoolers.

    I agree that more self-driving cars could fit on a road because computers can pay close, constant attention. Maybe V2V communications will someday happen, which could help, too, and ultimately lanes could be restriped narrower to get an extra lane (eventually, when all cars are self-driving). But as you point out, that magnifies problems when they occur. I see it like just-in-time procurement: it’s great when it works, but when there’s an earthquake in Thailand, the entire system seizes up because there’s no inventory sitting around to buffer the system.

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