Self-Driving CarAfter many years and nearly 1.5 million miles, Google’s Self-driving car’s perfect performance streak has come to a bitter end. For the first time since the project began, Google’s autonomous vehicle has mistakenly pulled into traffic, sideswiping a bus and causing a crash in the process.

Fortunately, the incident was minor and no injuries have been reported. The bus—a multi-ton vehicle—was carrying only 15 passengers and the Google car, of course, carried no passengers (save the test driver, of course).

Google reported, to the California Department of Motor Vehicles, that the autonomous Lexus SUV had successfully approached a right-hand turn by pulling near the curb to allow other vehicles to safely pass, going straight through the intersection. However, when the bot had tried to move back towards the center lane to avoid sandbags around a storm drain, it collided with a Santa Clara Valley Transportation Authority bus.

The incident occurred on Valentine’s Day, this year, and was the ninth report involving an autonomous vehicle. This is the first time, however, that the car was to blame for the incident.

Google reports, though, that the car made a mistake because of a fairly recent software tweak the company had made.

In the transit authority report, Google notes, “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. 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 report indicates that the robot car did, in fact, detect the approaching bus, but instead of waiting for it to pass, the computer predicted the bus would yield because it was approaching from the rear. Even the on-board test driver—who is supposed to take control in order to avoid accidents, and who had been watching the bus in the mirror, “expected the bus to slow or stop.” Thus, he did not override the autonomous mode.

Google says, “This type of misunderstanding happens between human drivers on the road every day.”

Google’s car, which is a Lexus RX 450h, only received some minor damage to the left front fender and wheel as well as to a driver-side sensor. The impact, however, did bend a piece of metal within the accordion-like pivot point of the two-carriage bus.