Originally Posted by cerewa

If you build it with three wheels, even if it has a car-like body that protects passengers from rain, it can be classified as a motorcycle in the USA (probably many other places). That would mean it doesn't have to conform to automobile safety rules, which would tend to make it just as heavy/expensive as a 'smart' car.

Put two wheels in front and one wheel in back so it balances better when braking.