Analyzing a libertarian stance on traffic enforcement

John, who works for Apple, comes up with an idea:

What about using traffic lights to effect negative feedback? The lights would turn red when the average speed of traffic is too fast, and turn green when the average speed of traffic is too slow. Like a thermostat. Speed governance would still exist, but it would be implicit ("designed into the system"), not explicit in road signs ("laws"), or completely absent.

Despite the enormous difficulties inherent in modelling traffic flow, I suspect there are several mathematical papers waiting to be written on why this is a bad idea. Let's brainstorm some reasons, shall we?

Think about how a traffic light normally functions. The old traffic lights were set to switch from red to green to red again repeatedly, at a constant interval. Your presence at one of these lights has no effect on when it will change, because the interval is preset.

Some cities time the lights on heavily-traveled roads, so that if you're driving the speed limit, you hit nothing but green. Again, you have no effect on the traffic light's state, as the lights are still preset -- just more intelligently. (Unfortunately, too much traffic will cause congestion because there's just not enough lanes to carry all the traffic, negating the effect of the light timing.)

Newer traffic-light systems measure the traffic volumes on roads and give more green-light time to the roads with more cars, in order to avoid backups. In this system, your presence does have an effect on the traffic-light's state, but only as part of a collective. The system only pays attention to large traffic volumes, of which your car is but a single member.

In John's system, your driving has a much more direct effect on the traffic-light state. If you are driving extremely quickly in one lane while others are driving at the speed limit, you will increase the mean velocity even though your velocity is non-representative of the other drivers. And speaking of mean velocities, what happens when two opposing roads have average speeds above the speed limit? Should you give a red light to the traffic going the fastest? In this case, fast traffic is rewarded for going over the speed limit -- but only because they were slower than the really fast traffic. You definitely don't want to give a red-light to the slower traffic, because this would lead to groups of traffic competing to see who can go the fastest; you can see this defeats the purpose of this exercise (to indirectly punish fast traffic). We could give both speeding traffic flows red lights, but this would quickly lead to gridlock.

What happens when both roads have average velocities that are too slow? You can't give them both green lights; you might as well remove the traffic light! The same problems apply -- one group is rewarded for incorrect behavior.

Another big problem: driving conditions. You can get pulled over for driving at or below the speed limit if you are facing inclement weather, because even the speed limit is unsafe. How will this new system of traffic lights judge the appropriate speed? This has to be done by an intelligent being, not a computer, because it's a judgment call.

Here's another hypothetical situation: say you're on a single-lane highway, and a pack of cars is stuck behind a driver doing 5 mph below the speed limit. The pack gets frustrated, and one-by-one they start to pass the slow driver. Passing requires that you speed up considerably, so the mean velocity increases drastically. Thus, at the next light, they'll be punished, even though the drivers were taking a prudent action intended to increase traffic flow and avoid a backup.

Sorry John... I really do like some libertarian ideas, but this is not one of them. Readers, if you come up with more hypothetical examples of where this system would fail miserably, blog them and trackback to me!