Motorcoach travel remains the greenest mode of transportation, according to the American Bus Association Foundation’s recently updated environmental study of different modes of transportation.

The study compared motorcoach travel to travel by private automobiles, heavy urban rail, light rail, commuter rail, intercity rail, domestic air travel, urban transit bus, electric trolley bus, ferry boat, vanpool, demand-response, and transportation network companies (TNCs). For all modes both energy use and emissions are expressed in terms of units per passenger mile operated. The metrics used for energy intensity are passenger miles per diesel-equivalent gallon (pass-mi/DEG) and Btu per passenger mile (Btu/pass-mi).

Motorcoaches on average used 493 Btu/pass-mi and produced 37 g/pass-mi of carbon dioxide. On average, motorcoaches use the least amount of energy and produce the lowest carbon dioxide emissions per passenger mile of any of the transportation modes analyzed.

The most energy- and carbon dioxide-intensive mode is demand-response at an average of 15,281 Btu/pass-mi and 1,101 g CO2/pass-mi. Vanpools on average produce two-and-a-half times as much carbon dioxide per passenger mile as motorcoaches, commuter rail produces more than four-and-a-half times as much, two-person car pools produce more than four-and-a-half times as much, and single commuters produce more than seven times as much.

On average TNCs are slightly less energy efficient than single commuting, using 5,029 Btu/pass-mi and emitting 374 g CO2/pass-mi. This is because, on average, TNCs only generate 0.95 passenger miles per vehicle-mile-driven, compared to one passenger mile per vehicle-mile for single commuting. TNCs carry an average of 1.5 passengers per trip (not including the driver), but for every 5.2 miles driven with passengers, the driver travels three miles empty, either waiting or driving from the last drop off to the next pick up.

The future of eco-friendly motorcoach travel will even look better than it does today, as more new fuel-efficient vehicles enter the market and replace current vehicles over the next 10 years, emissions per-passenger-mile from motorcoach will fall, according to the Foundation.

To view the full report, click here.