In the book, Evan says "5 or 6 long tubes which would contain the huge rubber bands extended the length of the car. Then these would be connected to a transmission which would wind up the rubber bands when you stopped. When you wanted to go, the rubber bands were unleashed to assist the engine in powering the car." Evan says the bands never made it into the test car.
He says the rubber bands exploded in the lab and staff had to run for cover. The test car, Evan says, became a push car waiting for a "breakthrough in durable rubber bands." You might laugh but Evan has far more serious stories about green car concepts at Chrysler. He says "a technician gave his life when a flywheel in a test cell disintegrated." Flywheels are a way of storing energy without chemicals.
[Source: Common Sense Not Required]