This part of Google's driverless-car crash report doesn't add up

Google is taking some responsibility for the incident, saying the minor fender-bender would never have happened if the autopilot hadn't misjudged. Photo / Bloomberg

We learned this week that one of Google's driverless cars was, for the first time, the cause of an accident.

The car was in the far right lane of a major thoroughfare. As its computer prepared to execute a turn, an obstacle near the curb forced the car to move left, back into traffic - and straight into the side of a passing bus.

Google is taking some responsibility for the incident, saying the minor fender-bender would never have happened if the autopilot hadn't misjudged. But the bus driver didn't slow down to allow the car back into the lane, either, Google points out, so it has reworked its software so that "our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles."

What we have, then, is a minor accident that mostly shows how complicated the human experience of driving really is - and how hard it is to replicate that same behavior in a machine.

But others say the unprecedented crash highlights the dangers ahead for driverless car makers. What happens when Google's vehicle injures someone - or worse, is involved in a fatal accident?

In that light, Google's prescribed fix - adjusting how the car interacts with "large vehicles" - seems like it merits a little more explanation.

Is there really something unique about how buses and large vehicles behave that preordained this crash?

Maybe; buses certainly are bigger and need more stopping room than a typical car.

Google itself points out that "this type of misunderstanding happens between human drivers on the road every day" and is a "classic example of the negotiation that's a normal part of driving," suggesting what occurred between the bus and the car is something that could have happened in any number of variations.

It's just as easy to imagine the driver of an SUV, sedan or a pickup truck behaving like that bus driver did - declining to yield. Without going into the bus driver's motivations, some people behave this way because they're in a hurry. Others might do it because they're feeling vindictive or aggressive. Why does being a bus or "other large vehicle" have all that much to do with it? Is a bus driver truly, statistically less likely to slow down or stop compared to a taxi driver?

Maybe Google's research suggests the answer is yes. The company didn't respond to my request for clarification, though, leaving us to wonder whether Oh, we've fixed it to account for buses now! is really all that satisfying when the human experience suggests large vehicles aren't the only kinds that will cut you off.