Waymo's depot in Chandler, Ariz.
Waymo's depot in Chandler, Ariz.
Photo: Waymo

Reducing traffic deaths caused by driver error has been the main promise of self-driving-car technology, a promise industry has used to justify billions of dollars of investment and the rush to get automated technologies on the road without much regulation. But a study from an auto safety watchdog says autonomous vehicles might only prevent a third of today’s serious highway crashes.

Researchers say the problem is with the way autonomous vehicles are being programmed, mimicking the way people drive today instead of safer driving methods, according to the study from the Insurance Institute for Highway Safety, a safety research organization funded by the insurance industry.

Automation will have the biggest safety benefit in crashes when the technology can pick up things that humans can’t.

But about two-thirds of crashes are from other causes, such as bad judgments, incorrect assumptions about what other vehicles will do, and inadequate evasive maneuvers—crashes that are likely to still happen even if the cars are driving themselves, the IIHS study says.

Self-driving cars will be most effective at preventing crashes when their sensors pick up potential hazards that the human driver does not see, or when the driver might be incapacitated, the IIHS says. Designers will need to prioritize safety over rider preferences if autonomous vehicles are to live up to their promise of being safer than human drivers, said Alexandra Mueller, a research scientist at the IIHS and lead author of the study.

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“Building self-driving cars that drive as well as people do is a big challenge in itself,” Mueller said. “But they’d actually need to be better than that to deliver on the promises we’ve all heard.”

The IIHS studied the driver errors from a nationally representative sample of more than 5,000 crashes involving serious injuries. Only a fraction of these injuries were due to the kinds of sensing and perceiving errors that self-driving cars are most likely to prevent. An even smaller fraction were due the human driver being drunk or drowsy, or using drugs.

The study has implications for lawmakers and regulators considering overhauls of traffic-safety laws to make it easier to roll out self-driving cars, says Ethan Douglas, senior policy analyst for cars and product safety at Consumer Reports. Without strong safety standards, the industry could proceed with “reckless deployment and put people in harm’s way,” Douglas says.

“Self-driving cars have a lot of long-term potential, but the auto industry has made promises it can’t keep,” Douglas says. “Instead of blindly riding the hype train, Congress should instead require proven safety features on all new cars that would make streets safer right now.”