ure idea is flawed, where do u propose we run these cars at a constant 80 or above where momentum would carry us through.
at a motorway perhaps? how many cars travel every day on the motorway for this idea to be feasible?
below 80 every car travels in the city, where mileage is horrible and people need an alternative way of getting around but your system dosent support it there.
2nd, 1st you say its a generator, now its a car system??