APTA calculates the average cost of taking public transit by determining the cost of the average monthly transit pass of local public transit agencies across the country. This information is based on the annual APTA fare collection survey and is weighted based on ridership (unlinked passenger trips). The assumption is that a person making a switch to public transportation would likely purchase an unlimited pass on the local public transit agency, typically available on a monthly basis.
APTA then compares the average monthly transit fare to the average cost of driving. The cost of driving is calculated using the 2016 AAA average cost of driving formula. That formula is based on variable and fixed costs. The variable costs include the cost of gas, maintenance and tires. The fixed costs include insurance, license registration, depreciation and finance charges. The comparison also uses the average mileage of a mid-size auto at 23.1 miles per gallon and the current price for self-serve regular unleaded gasoline as recorded by AAA each month. The analysis also assumes that a person will drive an average of 15,000 miles per year. The savings is based on the assumption that a person in a two-person household lives with one less car.
In determining the cost of parking, APTA uses the data from the 2012 Colliers International Parking Rate Study for monthly unreserved parking rates for the United States which is the most recent report available.