Desert Sun: On the outskirts of Los Angeles, inside a nondescript laboratory building, a man in a yellow T-shirt and helmet sits on a stationary motorcycle, looking intently ahead. The bikes back wheel is spinning, and a long orange tube connects to its exhaust pipe. A fan roars, mimicking wind. Nearby, on a computer screen, colorful lines show the concentration of pollutants emitted from the motorcycle, such as nitrogen oxides and carbon dioxide. This is an emissions test, and the rider must calibrate his...