Teaching a computer to drive a car is easy. It’s predicting the behavior of other drivers that’s hard.

Google says its driverless cars have been involved in 16 crashes over the past six years, and, as The New York Times reported, every one of them was the result of human error.

The most recent accident occurred on August 20, when a Google car slowed for a pedestrian, then the Google employee inside the vehicle manually applied the brakes. The car following rear-ended the Google mobile, sending the employee to the emergency room for mild whiplash.

Experts in the developing field of autonomous vehicles say a big challenge ahead is programming self-driving cars to know how to react to cars driven by humans.

“The real problem is that the car is too safe,” Donald Norman, director of the Design Lab at the University of California San Diego, who studies autonomous vehicles, told the Times. “They have to learn to be aggressive in the right amount, and the right amount depends on the culture.”

Google reported earlier this year that its cars have driven nearly 1 million miles on autopilot and now average about 10,000 self-driven miles a week. The cars have traveled another 700,000 miles with humans controlling them.

Other problems have come up when the Google car is at a four-way intersection and can’t figure out when it’s its turn to go. Humans “make eye contact.” John Lee, a professor of industrial and systems engineering and expert in driver safety and automation at the University of Wisconsin, told the Times. “On the fly, they make agreements about who has the right of way.”

-Noel Brinkerhoff, Steve Straehley

To Learn More:

Google’s Driverless Cars Run into Problem: Cars with Drivers (by Matt Richtel and Conor Dougherty, New York Times)

Humans at Fault in Self-Driving Car Crashes (by Jerry Hirsch and Joseph Serna, Los Angeles Times)

Google Driverless Cars in Accidents Again, Humans at Fault — Again (by Marco della Cava, USA Today)

Google Self-Driving Car Project: Monthly Report (Google) (pdf)

Driverless Test Cars Have Perfect —Unverifiable—No-Fault Crash Road Record (by Ken Broder, AllGov California)

If a Driverless Car Gets a Ticket, Who Pays? (by Noel Brinkerhoff and Danny Biederman, AllGov)