A Google self-driving car is seen in Mountain View, California, on May 13, 2014. A white Lexus cruised along a road near the Google campus, braking for pedestrians and scooting over in its lane to give bicyclists ample space. AFP PHOTO/Glenn CHAPMAN

One of Google’s driverless cars has been involved in an accident for the first time in a situation where human drivers rely on the normal social etiquette of the road to avoid scrapes, according to an accident report filed in California.

In a filing with the California Department of Motor Vehicles, Google said its car had been trying to pull out into slow-moving traffic on Valentine’s Day when a bus driver did not slow to leave room, causing a minor collision.

The incident highlights the challenges of programming machines to deal with the sort of social situations that humans encounter every day on the roads, but which are beyond robots to resolve, experts said.

It also threatens to cast an unflattering light on the technology at a time when Google is fighting a proposed California rule requiring autonomous vehicles to have human drivers on hand to override their controls in emergencies.

However, the company suggested that the accident would have occurred even if a human had been at the wheel, while adding that it had already adjusted its algorithms to take account of the lessons from the scrape.

“There are all sorts of social clues that people abide by that are hard to programme into a car,” said Jerry Kaplan, a serial technology entrepreneur and author of a recent book on robotics. “There was nothing terrible about this, no one got hurt or killed. But it will be a long time before the cars can be driven in heavily used streets and abide by the same social conventions people use.”

In a blog post on Monday, it blamed the accident on a “tricky set of circumstances” caused partly by an adjustment it had made to the car’s algorithms weeks earlier to help it drive more like a human.

“This is a classic example of the negotiation that’s a normal part of driving — we’re all trying to predict each other’s movements,” the company said. “We clearly bear some responsibility.” However, it also said that a Google employee in the car had also believed there was room to pull out.

The car had pulled close to the side of the road to make a turn, leaving room for other vehicles that were carrying on straight ahead to pass in the same lane — a manoeuvre Google said it had programmed into the car to make it a more considerate driver.

After finding its path was blocked by sandbags that had been placed round a drain, the car was forced to move back out into the line of traffic, causing the accident.

Google said it had already programmed lessons from the accident into its software, along with its findings from running simulations of thousands of similar situations.

“From now on, our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future,” it said.

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