Designer Da Feng created the Gym Car mockup that includes a near-complete home gym as well as a Batmobile-esque carbon fibre exterior. No word on the safety of doing bench-presses while driving.
The car's interior features a step machine, rowing machine, bench press, pull-up simulator and weights, and the energy outputted during a workout would go to powering its batteries. The exterior design of the car is supposedly inspired by World War II fighter planes, which sounds a lot more professional than "inspired by Batman."
Given the many laws prohibiting something as easy as talking on a phone while driving, we've got to believe the transit authority would frown upon any combination of exercise and driving, but I could see the benefit of a little stationary bike or something to help pass the time during a long commute. [Wired]