From time to time, the American Public Transportation Association (APTA) will publish transit savings reports that essentially compare the localized monthly cost of taking transit versus the monthly cost of driving. It’s obviously a simplified comparison, but a fairly credible baseline to examine the cost differentials between the two modes. The national savings, on average, amounts to $816 for the month of November, and $9,797 when calculated over the whole year.
The list of the top 20 cities puts Seattle at 4th among the company of San Francisco and Philadelphia. According to APTA, a Seattleite saves $992 a month on average, just by switching to transit. The methodology:
APTA calculates the average cost of taking public transit by determining 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 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 2011 AAA average cost of driving formula. AAA cost of driving formula is based on variable costs 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 23.4 miles per gallon and the price for self-serve regular unleaded gasoline as recorded by AAA on November 18, 2011 at $3.38 per gallon. The analysis also assumes that a person will drive an average of 15,000 miles per year. The savings assume a person in two-person household lives with one less car.
What the report doesn’t take into account is the employer-paid fare subsidy for transit users or the
upfront vehicle purchase price parking subsidy for car users, both of which represent largely sunk costs that aren’t readily apparent each time a trip is made. While I suspect that the differential would widen vary considerably* if those accommodations were made, that could only be assumed if mode use were mutually exclusive. Since many transit users do own cars, it would be interesting to see how numbers would stack up if costs for both were factored together.
*Depending on locality, driving costs could vary with parking costs; the counterclaim, of course, is that in places where parking is free, those expenses are still passed onto the employee in another form. Quantifying that, however, would be beyond the scope of such an analysis.