Right, this was probably an expensive INS (e.g. ring laser gyro) + GPS system. I imagine they would use something like this for a prototype, because they can get precise acceleration information without having to recalibrate after changes to the vehicle. The good news is that it is easy to get acceleration data for cars because they only have one axis of rotation, and they have wheels that are always on the ground. For production cars with this sort of technology, they can probably just use the speedometer along with something that measures how much the front wheels are turned. Maybe they will throw in a cheap INS to detect loss of wheel traction or otherwise improve the quality of the speed/acceleration data.
Of course, this only helps for navigation, which is probably the easiest part of the problem. Collision avoidance would probably be done with cameras, radar, ultrasonic ranging, etc.