[getalyft]

How about just programming human driven cars to obey speed limits (downrated in bad weather or visibility conditions). Many accidents are caused by people driving at an unsafe speed (who has not gone into a turn a little bit too fast). No AI needed, just a speed limit overlay onto existing GPS maps, plus a bit of logic to reduce speeds in certain conditions (night, low visibility, etc).

[asark]

Unexpected (by the driver) braking, possibly while making a turn, or controls failing to respond (the accelerator, say) seems more dangerous than the status quo.

Plus you'd have to roll it out everywhere at once, or my merge onto a 60mph limit highway where flow-of-traffic is closer to 75, in my software-crippled car that thinks I shouldn't exceed or maybe even match the speed limit in the on-ramp, is gonna be way more dangerous than having no such feature.

Then there's GPS often not quite knowing where you are most of the time (the route-finding apps just guess a lot—watch what happens when you make a wrong turn and it takes a few seconds to correct, because it's just assuming the diff between where you are and the road you're supposed to be on is an error, because there often are errors that large)