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Leave the Driving to It

How would lives and landscapes change if every car had a computer in the driver’s seat?

Brian Hayes

The Road More Traveled

Almost 90 percent of American workers commute by car, most of them alone, with a median trip duration of just under half an hour each way. Although some people report that they enjoy this daily respite between work and home, many others find it tedious, and on the whole it seems a waste of human potential to spend so much time merely supervising the operation of a machine. If we didn’t have to keep our hands on the wheel and our eyes on the road, the time might be put to better use.

Other resources besides human attention might also be used more efficiently in a world of automated driving. Roadway real estate is one of them. Steven A. Shladover of the University of California, Berkeley, points out that only about 5 percent of the roadway surface is occupied by cars on a freeway running at peak throughput conditions (about 2,200 vehicles per lane per hour). Computer control, he suggests, could double or triple the density while keeping speeds constant. By squeezing more cars onto the same roads, we relieve pressure to widen highways or build new ones. Cars could be packed tighter both by narrowing the lanes and by reducing the headway between successive vehicles traveling in the same lane. Closer spacing is made possible in part because computers can maintain more precise control, both laterally and longitudinally. Equally important, automated vehicles can coordinate their motions through car-to-car data links, communicating not only their present position and velocity but also their intentions, such as changing lanes.

Communication is the key to many of the most attractive features of automated driving. (Indeed, Shladover suggests that the term “autonomous vehicle” is misleading in this respect; cooperation is more important than autonomy.) Consider the stop sign and the traffic signal: By forcing drivers to take turns at an intersection, these devices ensure that everyone gets access to a shared resource. But the stop-and-start regime of city traffic also causes congestion, wastes fuel and frays nerves. If cars could communicate with one another and with the roadway infrastructure, they could negotiate priority as they approached each intersection, adjusting their speeds to avoid conflict. Ideally, no car would ever have to make a full stop; traffic management would become a kind of precision choreography.

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