how can we produce electricity on roads with cars ?

Answer 1

This is a great question. Here's my suggestion. Since all vehicles already have rubber tires, just make an asphalt product with a higher powdered glass content to coat the highways. Then when you're driving, the cars build up a huge static electricity charge, that can be channeled into the flux capacitor to generate the 1.21 gigawatts needed to send you back to the future.
Or something along those lines.

Answer 2

That depends on how you intend to use that electricity. If you want some byproduct of driving that produces electricity specifically for other, non driving related uses then you might be out of luck. most of those schemes tend to increase the energy needed for driving and some can be quite dangerous.

However, if you want to make vehicles more efficient and less polluting then there are many options available. One of the best approaches may be using hybrid eclectic vehicles that utilize a fuel cell power plant. The fuel cell provides electric power to operate the vehicle. Then when you park (home, work, grocery store, etc.) you can plug the vehicle in and sell electricity back into the electric grid. It gets even better if you include some photovoltaic on the vehicle and park in the sun. Keep in mind that there are many possible derivatives to this approach.

Answer 3

This actually has been done, a small bridge has kinda a little teeter-tooter built in so as the cars drive over it, they push it down and this turns a crank which then turns a generator. They use the electricity to power the bridge and nearby structures.

But this may be free electricity for the bridge... but you can't make something out of nothing... each car is using a tiny bit extra gas to push down that lever, in the end the bridge is being powered by gasoline engines, so it certainly is not a 'green' friendly option.

Answer 4

How about micro windmills along the side of the road that generate small amounts of electricity from the wind that each car or truck generates? It won't change the amount of gas each car uses, unlike the ramp on the bridge tactic. Of course, the installation and maintenance costs would be pretty high -- maybe not worth the payback of the electricity....