It's only feasible right now in a controlled environment (all the drivers are the same AI and no humans doing unexpected things). Otherwise is a hard and complex AI problem.
But they have to be small, cheap and can't depend on you driving them to a dedicated parking lot.
On the other hand it's perfectly ok if they never go past 40 mph and need recharging twice a day - as long as they don't need the "client" to take them to the fuel station.