A week or three ago I read that if you divide the number of passenger miles ridden by the number of gallons of fuel used by the public transportation systems of many cities, you end up with a pretty lousy number (see here for the full scoop). That makes sense if the public transportation system runs lots of mostly-empty, big, heavy, diesel-hungry buses or trains or ferry boats.
Which made me wonder: how does our local public transportation system fare?
The National Transit Database gave me the number of passenger miles ridden in 2006 for the entire PVTA system: about 31 million miles.
And an email to the nice folks at the PVTA got the number of gallons of fuel they used last year (2007): about 1.5 million gallons.
Divide miles by gallons and you get about 20 MPG (that's not quite right-- I should divide 2007 miles by 2007 gallons; I'll update this post when the 2007 ridership miles are available).
20 MPG is lousy. The CAFE mandated fuel efficiency for single-passenger vehicles is 27.5 MPG. Unless you own a gas-guzzler, and especially if you're going somewhere with a friend, then the raw data says driving will use less gas than riding the bus.
But that's not really right. The "marginal cost" of riding the bus is probably pretty close to zero; add another person to the bus and it's not going to use a whole lot more fuel. At least, until the bus gets too crowded and you need to buy and run another bus to fit everybody. Then the marginal cost of that one extra person is ginormous.
I think the lesson is that it is not as simple as "bus good, car bad." Running lots of empty or mostly empty buses is worse for the environment (and our economy) than running smaller, more fuel efficient private cars or taxis. If we really care about the environment, then the fuel efficiency standards that we set for cars should also be applied to public transportation. Why not tell PVTA: "You must be at least as fuel efficient, on a passenger-mile-per-gallon basis, as the CAFE standard for single passenger automobiles (27.5MPG)."