Saturday, September 13, 2008


Limiting the speed of cars?

Kent Sepkowitz, a medical doctor, suggests, in a New York Times op-ed piece, that speeding kills and that we can solve the problem easily — that “there’s a simple way to prevent speeding: quit building cars that can exceed the speed limit.”

There’s one thing you can be sure of in life: when someone claims to have a “simple” solution, their plan is neither simple nor a solution. Such is the case here, as well, though Dr Sepkowitz has some valid points. Here’s what he gets right:

  1. “Speeding is [a factor in] 30 percent of all traffic deaths in the United States — about 13,000 people a year.”
  2. “There is [a] relationship between speeding and alcohol.”
  3. “Americans insist on the inalienable right to speed.”
  4. We could use toll-road information to compute a lower bound on drivers’ speeds, and ticket them accordingly. Indeed, I, too, have always wondered why we don’t, and I suspect, as Dr Sepkowitz does, that item 3 is the reason, and that “the public outcry would be deafening.”

So what does he get wrong?

First, and most obviously, he conflates speeding — exceeding the speed limit on a particular road — with exceeding some global maximum speed to which we could limit cars. To be sure, both are dangerous and the latter is worse. But the statistics are based on the former, and governing the maximum speed of cars would not have the effect he’s suggesting that it would.

A great many fatal collisions in which speed is a factor happen at speeds well below any reasonable maximum — say, when someone is driving 60 MPH where the speed limit is 35. We do not have the infrastructure to prevent cars from speeding, in that sense.

Speeding is not a priority for the NHTSA because, while it’s a factor in (not “the cause of”) a great many traffic deaths, it’s often a contributing factor, not the primary one. Coupled with drinking, it’s the drinking that’s the real problem. Similarly for driver inattention, impatience, sleepiness, and other factors. When we look only at cases where speed exceeded 75 MPH, the hard limit Dr Sepkowitz proposes, the case is even stronger. Which will prevent more deaths on the whole: mechanically limiting car speeds to 75 MPH, or getting everyone to wear seat belts? It’s the latter, and that’s why the seat belts are a higher priority.

It’s also not correct to say, “Speeding, after all, substantially reduces fuel efficiency due to the sheering force of wind.” It’s not that simple; if it were, we could maximize fuel efficiency as well as safety by limiting everyone to 20 MPH — and I’m quite sure that even Dr Sepkowitz wouldn’t accept that. No, given a particular combination of engine design, body design, and road, there will be a speed that optimizes fuel efficiency. That speed might be less than or greater than the speed limit, depending upon what the limit is for that particular road. “Speeding” does not use fuel inefficiently. Driving at 85 MPH probably does.

There are also good reasons to have headroom, to be able to go faster at certain times than one might normally allow. Probably, the suggested 75 MPH limit handles those cases acceptably.

All that said, I don’t mean to imply that I think Dr Sepkowitz has a bad idea here — only that it’s not as good as he thinks it is. He’s right that there’s no good reason to have cars that can go faster than 75 MPH or so on the American roads. Just because it doesn’t solve the whole problem doesn’t mean that it isn’t worth a go.

On the other hand, many of us remember the period when speedometers were limited to a maximum reading of 85 MPH — even if the car could actually go much faster. It didn’t last. Dr Sepkowitz is quite right: “Americans insist on the inalienable right to speed.”

I’ll also note that speed limits are much higher in parts of Europe — and are famously absent on sections of Germany’s Autobahn — without higher fatality rates. The roads are built for the high speeds, and the drivers are used to different habits. Training is important. It’s interesting to be riding in the left lane of the Autobahn, passing cars in the right lane as though they were standing still... and realizing that the “slow-pokes” in the right lane are going 85 MPH (130 KPH).

If you think Americans would object to having their cars’ speed mechanically limited, go suggest it to the Germans.

1 comment:

The Ridger, FCD said...

When I was stationed in Berlin, when you drove from Checkpoint Bravo to Alpha (Berlin to Helmstedt), the MPs took down the time you went through. The primary reason for this was so that if you were overdue at the next checkpoint they could go look for you - were you in an accident, lost in East Germany, doing some illicit sightseeing, or defecting? - but that didn't stop them from writing you up if you got there too soon. (Sure, there was no speed limit on the Autobahn in East Germany, either, but the Army had one you were supposed to obey.)