Driverless cars must deal with motorists, and it’s proving more difficult than expected. The New York Times reported this week one surprising problem encountered by Google’s autonomous vehicle project: the difficulty of interacting with human drivers. Apparently the computerized cars are not completely prepared for drivers who break the rules.

One Google car, in a test in 2009, couldn’t get through a four-way stop because its sensors kept waiting for other (human) drivers to stop completely and let it go. The human drivers kept inching forward, looking for the advantage – paralyzing Google’s robot.