Trough cheap technology it will be possible to use the passing of vehicles to illuminate the city

— http://www.alphagalileo.org/ViewItem.aspx?ItemId=136895&CultureCode=en

Someone in Mexico wants to build a sort of below-ground bellows system to produce “sustainable” energy from passing cars. Or pedestrians. Apparently not aware that this is a means of decreasing the fuel efficiency of the traffic, hence not exactly sustainable.  

(Well, maybe if it’s just pedestrians, but then, does this mean that everyone, including people who already have walking difficulties, are to have their movements impaired?)

Conceivably it could be a method of street lighting — where you only have light when there’s moving traffic — but still not particularly sustainable (compared with energy collected in the day and redistributed at night, which can also be triggered by moving traffic or pedestrians; and I think it’s been done).

Or, maybe if it was implemented downhill-only. (Vehicles having already used the input energy to get to the top of the slope.) Is this doable?

(The amount of energy extractable on a down slope would be slightly less per horizontal unit distance than on an upslope. But it might be a form of in-road braking assistance.)

But if so, i.e. if it could produce useful amounts of energy, would it not be the case that shaving the extra couple of inches off the tops of hilly roads would save the same amount of energy from fuel use, allowing another more efficient supply of lighting energy to be used at a slight net gain? Hence being a lower-tech solution to sustainability issues?

(The argument could be extended to the point where all roads were at a uniform height, and ran in deep cuttings or tunnels; but I expect there would be a maximum depth to which excavation could be undertaken before the energy cost of removal exceeded the potential gain, and I’m not going to try to calculate that.)

But in practice, who would ever design roads for improved efficiency? If there wasn’t some sort of flashy technical solution involved with which to impress the politicians . . . 

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