Trident said:

Would you replace them with something else like trams or trains or buses or would it just be bicycles for everyone?

Would companies still be allowed trucks to make deliveries?

All of those.

A small fraction of the vast sums of money we would have previously paid for cars, their maintenance, and fuel costs, could be taken instead as tax revenue. This money could then provide a universal transport system, free at the point of need (Within "sensible" limits, agreed in parliament).

Also, given that the roads would not be congested with millions of single person cars (Just thousands of multi-person buses and public-free taxis), the workforce who would normally spend a portion of their day in traffic jams would become more productive. Transport of goods and services would also be swifter and more efficient.

A workforce would also be required to drive the new public transport vehicles, to build them and maintain them. Providing jobs. The public would have more money (Which they would normally spend on cars) to put back into the economy.

Oh... and the environment etc.