Simpler answer...
...railway tracks on roads! If all roads had tracks with automatic crossover points for turning off all cars could follow a set route punched in beforehand. Also this would prevent accidental pile ups. The other boon would be you could power the vehicles from the rail (People crossing the roads would need not worry as the power would be isolated and each car will detect obstacles in their path).
Any country roads/dirt tracks without rails you get a big noisy flashy warning to take over control and use traditional wheel based driving.
The gubberments could charge you on usage too.
Biting the hand that feeds IT
