Adaptive cruise control systems work by monitoring the road ahead using a radar or laser-based device and then use both the accelerator and brake to maintain a certain distance from the vehicle ahead. (Other variations can bring the car to a halt in the event of a potential accident).

These devices have been available on upmarket cars for ten years or more and are now becoming increasingly common. If you drive regularly on freeways, the chances are you regularly come across other vehicles being driven by these devices, especially in Europe and Japan (here, the density of traffic means that ordinary cruise control has never caught on in the way it has in the U.S.).

So how does the presence of computer-controlled vehicles affect traffic dynamics? Today, Arne Kesting and pals at the Technical University of Dresden in Germany provide an answer of sorts using a model of traffic flow in which both human and computer-driven cars share the road.

They say that the presence of computer-driven cars increases the amount of traffic that can flow on a road before jamming occurs. And the more of these cars, the greater the capacity becomes. “1 percent more [computer-controlled] vehicles will lead to an increase of the capacities by about 0.3 percent,” they say.

That’s interesting but there have been other studies suggesting that computer-controlled cars can lead to greater congestion and it’s not at all clear why Kesting and company’s analysis is superior.

Either way, the argument is probably moot. Computer-controlled cars are just the first step in what many expect to be a revolution in car travel. The big increases in traffic capacity are likely to come when cars are able to communicate with each other. This should allow entire platoons of vehicles to travel as one unit, with just a few centimetres gap between cars and the vehicle in the front communicating its intentions to all the others. Platooning should improve fuel efficiency, too.

Of course, that won’t be possible until there is a critical mass of computer-controlled cars on the roads. Even then there is a bigger hurdle to overcome of creating the legal framework in which all this can happen: imagine the insurance claims if one of these platoons were to crash.

The biggest challenge for the makers of cars that drive themselves is no longer technical but legal.

Ref: arxiv.org/abs/0912.3613: Enhanced Intelligent Driver Model to Access the Impact of Driving Strategies on Traffic Capacity