I suggest you look at a promising new technology from a company in Israel called "Innowattech"
They have recently been awarded a multi million dollar contract in Italy to install a system into a highway that converts mechanical energy into electricity. The system uses what is called "Piezo Electric Generators" that are placed under the surface of the road way. The generators converts the motion of passing vehicles into electricity.
You will find lots of valuable information on their site to include lots of press releases.
With the proposal of an infastructure bank this technology might offer a way for the DOT to generate income buy generating electricity from our highways and selling it to the local utilities.