Spotting a fire truck ahead is easy for people, not so for cars

A file photo of a Tesla Model S electric car that has crashed into a fire engine on Interstate 405 in Culver City, California. So far, Tesla is the only carmaker cited by the US National Transportation Safety Board in an accident investigation for how it designed its partially autonomous system, but the case highlights the broader limitations of similar technology. — KCBS-TV/AP

To the human driver, it would have been an obvious obstacle: a police car and fire truck, emergency lights blazing, blocking the lane ahead.

But to the Tesla Inc Model S traveling down a Southern California freeway last year on Autopilot, it was a far more vexing technical challenge that’s inherently difficult for the growing number of vehicles that automakers are equipping with driver-assist systems.