MOUNTAIN VIEW — A Google self-driving car has for the first time caused a crash, pulling into traffic and sideswiping a public bus.

No one was injured in the minor fender bender, but Google has adjusted the software for its fleet of autonomous cars to avoid future mishaps. Still, the incident underscored that Google's cars are a work in progress and — in the words of one critic — "aren't ready to cope with many everyday driving situations."

In a report to the Department of Motor Vehicles posted online Monday, Google said its Lexus SUV was attempting to make a right turn onto Castro Street from El Camino Real in Mountain View on Feb. 14. The car had pulled close to the curb to allow vehicles behind it to proceed straight, but when the car moved back into the center of the lane to avoid sandbags around a drain, it hit a Santa Clara Valley Transportation Authority bus, the Mountain View Internet search giant said.

The Valentine's Day crash was the ninth incident involving a Google self-driving car reported to the DMV in the past year. But it was the first time the car was to blame, a company spokesperson said.

The VTA noted that the bus, which had been carrying 15 passengers, was a "multi-ton vehicle."

"It seems safe to say that you should not pull out in front of a bus or into the lane when a bus is going by," said VTA spokeswoman Stacey Hendler Ross. "The bus doesn't stop in an instant."

The car's mistake arose out of a fairly recent software tweak, Google said in a February monthly report on its self-driving cars.

"When you're teeing up a right-hand turn in a lane wide enough to handle two streams of traffic, annoyed traffic stacks up behind you," the report said. "So several weeks ago, we began giving the self-driving car the capabilities it needs to do what human drivers do: hug the rightmost side of the lane. This is the social norm because a turning vehicle often has to pause and wait for pedestrians; hugging the curb allows other drivers to continue on their way by passing on the left. It's vital for us to develop advanced skills that respect not just the letter of the traffic code but the spirit of the road."

The robot car had detected the approaching bus, but "predicted that it would yield to us because we were ahead of it," Google said. The on-board test driver, who is supposed to take control of the car to avoid accidents, had been watching the bus in a mirror, "expected the bus to slow or stop" and apparently did not override the autonomous mode.

"This type of misunderstanding happens between human drivers on the road every day," Google said.

A police report is not required for minor accidents, and none was filed, according to Mountain View police. Google said its car was driving about 2 mphand the bus around 15 mph when the collision occurred.

Google's car, a Lexus RX 450h, received damage to the left front fender and wheel and to a driver-side sensor. The impact bent a piece of metal in the accordion-like pivot point of the two-carriage bus, Hendler Ross said.

In the wake of the crash, consumer advocate John Simpson of Consumer Watchdog called for mandatory police reports in cases of Google autonomous-car accidents.

"Heck, they're using our public highway as as their own laboratory, and that brings some obligation to put the public first," Simpson said. "This really shows the situation that we've seen repeatedly that demonstrates that these cars aren't ready to cope with many everyday driving situations. Merging back into the center of a lane, you ought to be able to do that without sideswiping a bus."

However, Bryant Walker Smith, a risk, technology and mobility expert at Stanford University and assistant professor in both law and engineering at the University of South Carolina, suggested that the accident doesn't mean much in the overall debate over self-driving cars.

"I'm no more or less optimistic about the technology or the rate of deployment after this crash," Smith said. "It is simply something that was going to happen eventually and doesn't change my sense that the technology has not yet been demonstrated to be ready over a wide range of conditions."

Google director Chris Urmson, in a Jan. 28 California DMV public workshop on the state's draft regulations for robot cars, acknowledged that Google's cars weren't ready for complete autonomy. But Urmson said Google opposes a draft provision that would ban robot vehicles without human operators from any testing or deployment on California roads.

Urmson said Google doesn't see much difference between a human driver "who we really don't trust" and no driver at all.

Contact Ethan Baron at 408-920-5011 or follow him at Twitter.com/ethanbaron.