Transit system efficiency varies with ridership
Certain forms of public transit may actually be worse for the environment than driving in a car, according to a U.S. professor.
The efficiency of a mass transit vehicle varies depending on the number of passengers onboard, Eric Morris, urban planning professor at Clemson University, told Freakonomics co-author Stephen Dubner on an U.S. radio show November 14.
“Obviously, the energy expenditure in moving around a transit vehicle per passenger mile depends on the number of passengers," Morris explained. "Whether you have one passenger in a bus or 40 passengers in a bus, you're going to be expending almost the same amount of energy."
Most buses in the U.S. ferry roughly 10 passengers at a time, whereas most cars have 1.6 occupants, Marketplace.org reports. According to Morris' calculations, that puts buses behind cars, efficiency-wise.
"Typically, moving a passenger a mile by bus requires roughly 20 percent more energy than moving a passenger around by car... So, just in terms of energy expenditure, bus actually fares worse than car."
Subways and trains, however, have cars beat, Morris says. On average, they use roughly two-thirds of the energy-per-mile-per-passenger a car does, save for New York's hyper-efficient and much-used underground transit system, which uses a lot less.
Morris points out that a city or town isn't necessarily saving energy when it builds a new public transit system — people have to use the system. In some U.S. cities – he cites memphis, Cleveland and Pittsburgh – the transit system is actually worse on the environment.
Dubner suggests U.S. transit systems could be made more efficient if municipal governments incentivized transit use by making personal car use more expensive, via taxation.