a crosswalk. february, a google autonomous car sideswiped a bus while trying to pass. in may, a tesla driver died in a self-driving crash but investigators could not attributed to the autopilot system. >> the things that go wrong in the driverless car world are going to create a more durable system. >> coopers 43 self-driving cars travel up to 20,000 miles a weea human muscle take control approximately every eight tenths of a mile. >> the theory that if you remove the driver, you remove driver era, there are defects. if the automation doesn't work, then what? >> airplanes are much safer than car transportation. it's going to take a while before we get driverless vehicles to the same level of safety as air transportation. >> as for the accident friday in arizona, police did cite the human driver for failing to