From APTA:
WASHINGTON, DC – Individuals who ride public transportation can save on average $9,062 annually based on the October 5, 2009 national average gas price and the national unreserved monthly parking rate.
“The Transit Savings Report” released monthly by the American Public Transportation Association (APTA) calculates the average annual and monthly savings for public transit users. The report examines how an individual in a two-person household can save money by taking public transportation and living with one less car.