There is no need to try and dictate the type of fuel, either.
But I'm interested to understand why people think a robotised taxi service would be much cheaper than human-driven taxi service. Is the driver really the highest marginal cost in the system? Does removing a driver really drive costs down that much? I wouldn't have thought so.
Oh, and your desire to ban manual driving is never going to fly. The most you would want is perhaps dedicated driverless roads where you aren't allowed to drive - much like bus lanes are now. That would allow for higher speed possible if computer systems can show they can safely transport occupants (or goods) at speeds higher than human drivers.