Not a bad idea, but the example given would just work like another toll: Any energy generated would just be created by even more energy used by the car to climb over the strip.

But there is a useful way to capture energy normally turned into heat by car brakes. Regenerative braking is an important part of many of the new super-efficient electric car designs. In a setting with a constant stream of decellerating cars (ie. a toll booth), you could move the regeneration out of the cars and into the pavement. For example, cars moving over a long array of magnets and field coils would slow the cars by transforming momentum into electricity. This way, every car would be subject to regenerative braking.

i disagree with the fact that there would be a "toll" on energy if you were to use the car to push down on a piston- it would be very easy to implement:

something like a ramp on a hinge, facing so the car drives up it, with the pistons/generators on the far end. As the car drives up the ramp, it applies force to the pistons. Strong springs would apply the force back at no energy cost. The car would already have been moving, and the car needs not expend any more energy as their primary goal when driving towards the toll booth is to slow down anyway.

Heck, just build new toll booths at the top of hills.

That's the idea man! God must be slapping people with devine intervention, because the very same idea occured to me about 2 months ago. The vehicle is a tremendous source of energy in itself! Imagine how many cars! I too realised that the toll booth would be the ideal spot for a mechanism somewhat related to the "do not reverse-severe tire damage" style device. But if one thinks further along with this idea...the end of energy grid woes are not so far away. This type of device does not have to be limited to toll booths. After some ingenuity and creative experimentation, a design could result which would be suitable for higher speed. Then you could have them up and down the freeway, a near unlimited amount if you wanted too.

The main problem with most items in the Energy category is forgetting that you can't get something for nothing. The energy to power all this stuff must come from somewhere. In this case, it comes from the automobile motor. I believe that the efficiency of most motors in converting gas to energy is relatively poor when compared to power plants. The additional loss in converting it back from motion to electrical energy makes it MUCH less efficient. A better goal in regenerating energy is to find a source of energy that would otherwise be lost (i.e. it's not a source that is already being generated for another purpose) and trying to harness that.

I agree that gasoline engines should be on the way out. The problem with getting rid of them is that cars will be running on electricity. Eletrical demands will be that much greater. We will need more power plants, requiring more production by oil, nuclear, dams, etc... The demand will be shifted from engine to powerplant.

THIS IDEA IS A WAY TO GO! Vehicles are like heavy rocks in motion that could produce back into the energy grid. Imagine large electric powered trains on tracks where the tracks can gather energy from the train's weight, while powering the train at the same time. Of course there would be a loss of energy, but the return could be substantial.

Enter thermodynamics- Energy cannot be created or destroyed.

Hybrid cars gain some of their efficiency by using an electric generator hooked to their wheels- AS A BRAKE! The generator resists turning, and slows the car.

Now imagine driving down the highway with your brakes on. Not the picture of efficiency, is it?

This is an interesting proposal. The idea of pistons would potentially create a very bumpy ride. However, if alternating coils were in the roadway where one is the equivalent of a stator and the next the rotor, the metal in the car moving over those coils might impart the generation of electric current.

However, the distance from the metal mass of the car to the roadway is so large, I'm not sure the energy produced would be significant.

Also, if the energy produced is significant, that would also mean the metal is heating up somewhat from induction coupling.

Potentially, one might save energy by recovering what would normally be spent on braking. But a better saving would be not to slow down in the first place so you don't have to spend the energy to accelerate.

An alternative would be to make toll roads where camera's capture driver photo and license plate information and the toll bill is emailed or snail mailed to the person's home address. This also has the additional merit of reduced personnel.

A manual self-serve toll gate would be available for those not wanting to be billed.

This idea has been implemented already. Instead of losing momentum by stepping on the brakes, an embedded ramp directly in front of the booth slows that car and generates electricity. Good idea.