« The Tragedy of the Commons vs. The Three Musketeers | Main | Driver behavior a tragedy of the commons after all? »

Tail-gating tragedy reversed?

We know that one selfish driver can slow everyone down by weaving in and out of traffic, but is the reverse also true? William Beaty claims to have figured out how one driver can eliminate those annoying, slow moving "clots" of cars. He simply maintains a longer-than-usual following distance when he approaches a clot. That prevents the clot from growing at the rear, while it gradually evaporates at the front. I would have thought that might lead to another clot behind him, but he says actual road tests show it improves traffic flow both in front and behind. Apparently the key is driving at a constant rate, which would be impossible if he were tail-gating the clot, but isn't that hard to do if you leave enough space in front of you to buffer speed fluctuations of the car ahead.


Some people don't like to leave extra space in front of them because people will cut in front (either by passing or from a neighboring lane), but I've found that doesn't happen as often as you might expect. Beaty's explanation is that aggressive drivers pass you or move into your lane, but then they're gone and you accumulate better drivers behind and around you.

He's also got an impressive animation apparently showing that increasing following distance and letting people merge makes traffic flow faster when constricted by lane closures.

Is there a tragedy of the commons here? I always try to leave three or four seconds ahead of me because I think it increases my own safety and figure I'll only arrive at my destination one or two seconds later than if I left a two-second gap. (OK, two seconds times the number of people who cut in front of me, but that still never adds up to more than a 10 seconds or so.) If increasing following distance is the best strategy for individuals and also helps everyone else, then this isn't a real tragedy of the commons, just a widespread failure to recognize enlightened self-interest.

What I'd like to see is a realistic traffic simulation to answer these questions:
1) how much does aggressive driving decrease travel time for the perps? (On an open road, driving twice as fast gets you there in half the time, but what about in traffic?)
2) how much does it increase their chance of having an accident?
3) what are the effects on the rest of us?
4) assuming that most drivers follow too closely, what happens if a few drivers increase their following distance? How does it affect travel time and accident rates for these drivers, and how does it affect overall traffic flow?

There's another possible connection to Harding's original essay. Remember his suggestion that some problems have no technical solution? This might actually be a case in which a technical solution would work pretty well. I guess there would still be an element of "mutual coercion, mutually agreed upon", in that the solution may depend on government-mandated liability insurance.

Post a comment

(If you haven't left a comment here before, you may need to be approved by the site owner before your comment will appear. Until then, it won't appear on the entry. Thanks for waiting.)


Type the characters you see in the picture above.