By cutting down on the number of people using cars, public transit also decreases traffic congestion, allowing drivers and their passengers to get to their destinations faster (and burn less fuel in the process).
The simplest answer is that it gets cars off the roads. The Environmental Literacy Council estimates that public transportation keeps 1.5 million tons (1.4 million metric tons) of carbon dioxide emissions out of the air every year simply by giving people an option besides driving their cars. The council also credits public transportation with saving 1.4 billion gallons (5.3 billion liters) of gasoline annually. While impressive, statistics like these also make a lot of sense. By cutting down on the number of people using cars, public transit also decreases traffic congestion, allowing drivers and their passengers to get to their destinations faster (and burn less fuel in the process).