Even with the coming of flying cars, the roadways will still be used, but much less often. In the same way that old cars are still being used today (2008), old cars will still be an option for use.
Likewise, freight carriers – tractor trailers, big-rigs, and very large vehicles will still use the roads on into the next century. Petroleum will still be the fuel of choice up until the midpoint of this century. It will gradually be used less as less after the 2050 coming forth of the new energy.
Petroleum will still be used in making so many millions of products but the new energy of 2050 will eventually replace it’s use in propelling vehicles.