You are thinking of http://sawstop.com/why-sawstop/the-technology. The problem with your comparison is that cars already have brakes. Driverless cars would improve reaction time, but can't do anything to affect stopping time. You would need to activate some additional braking system.

<snark>I also don't see how a car could dive below the roadway instantly. Roads don't have car-sized holes in them. Usually.</snark>