True, but it doesn't have to. The root of the problem is the vast number of cars on the road. Much of the emissions from a car come from the manufacture of the car, not just the use of it.
When you think of the wisdom behind millions of cars sitting in rush hour gridlock (on government designed roads), emitting smoke and chemicals into the environment and wasting hours of drivers' valuable time, think of the grand purpose -- so that people can live in the suburbs at an artificially low price.
