On Mon, 05 Sep 2005 02:46:11 -0400, "David W. Poole, Jr."
Perhaps you've seen those virtual trains of experimental cars that they test on the I-15 express lanes down in San Diego County on the Discovery channel or TLC. This stretch of road has small magnets installed at periodic intervals in the road surface. Presumably the cars have hall effect sensors installed along their sides to that they can determine their relative position on the road. The TV shows that show these cars never go into the technical details of the algorithms involved; my guess would be some sort of PID or PLL or similar difference feedback technique to automatically correct the difference between the desired position within the lane and the actual position of the vehicle. The cars themselves also communicate directly, so they know each others' positions, speeds, etc. They probably even inform each other of events such as braking or hazard avoidance. IIRC, the cars also use radar to sense possible obstructions ahead as well as determine thier position relative to the cars in front and behind.
If we wanted to instrument every road and equip every car with the control devices, we could have self-driving cars today. However, it makes more sense to spend the money on more research to make the systems usable under less controlled conditions and on uninstrumented roads.
