Google does a lot of driving in simulation, using data captured by real vehicles. They log all the raw sensor data on the real vehicles, so they can do a full playback. They do far more miles in simulation than they do in the real world. That's how they debug, and how they regression-test.
For near-misses, disconnects, poor decisions, and accidents, they replay the event in the simulator using the live data, and work on the software until that won't happen again. Analyzing problems which didn't rise to the level of an accident provides far more situations to analyze. They're not limited to just accidents.
See Chris Urmson's talk at SXSW, which has lots of playbacks of situations Google cars have encountered.[1]
For near-misses, disconnects, poor decisions, and accidents, they replay the event in the simulator using the live data, and work on the software until that won't happen again. Analyzing problems which didn't rise to the level of an accident provides far more situations to analyze. They're not limited to just accidents.
See Chris Urmson's talk at SXSW, which has lots of playbacks of situations Google cars have encountered.[1]
[1] https://www.youtube.com/watch?v=Uj-rK8V-rik