It turns out we have all the tech needed to make autonomous trains, and we’ve seen robotrains running in limited capacity since the late 1960s. The problem isn’t technology. It’s line of sight, and the massive distances trains need to identify and react to obstacles and bring a few hundred tons of steel and cargo to a stop safely.
“The stopping distance of a train is much longer than a car,” says Dr. David Clarke, director of the University of Tennessee Center for Transportation Research Center. “It could be close to a mile.”
Unlike a car, where friction between the tires and road is much higher, metal wheels on metal track makes stopping a whole lot harder. The radar-based adaptive cruise-control systems fitted to most luxury cars these days could conceivably be adapted to trains, but the massive time and distance needed to slow the train means there’s no effective way such a system could see far enough ahead to react in time. And there are just too many things that can obstruct the track.