When you fill up your fuel tank at a gas station, have you ever seen a Department of Transportation official measuring the wheelbase of your car? Neither have I, but the Federal Highway Administration’s Highway Statistics, table VM-1, reports the total amount of fuel used, to the nearest 1,000 gallons, by vehicle type. Those vehicle types include buses, motorcycles, large trucks, and short- and long-wheelbase automobiles, with the division being wheelbases of 121 inches.
The government has a pretty good idea of how many miles Americans drive each year based on 5,000 traffic counters all across the country. To be honest, the traffic counters are really only on major roads, so the miles driven on local roads are just estimates. Even on the major roads, I doubt the traffic counters are good enough to detect the difference between vehicles whose wheelbases are shorter or longer than 121 inches.
Even more difficult is determining how many gallons of fuel are used by each type of vehicle. As near as I can tell, these numbers are based on a model and I’m not sure some of the assumptions in the model are valid. As I’ve noted before, I’m particularly suspicious of the bus numbers, but I have to wonder about motorcycle and short- and long-wheelbase autos as well. Continue reading
