Transit Ridership and Emissions per Mile

Public Transportation’s Role in Responding to Climate Change (20 page pdf, Federal Transit Administration, U.S. Dept of Transportation, Jan. 2010)

Also discussed here: Transit emissions and the importance of ridership (Sustainable Cities and Transport, Apr. 25, 2010)

Often public transit advocates claim that transit pollutes less than single occupancy vehicles but, as this article points out, the comparison depend son the passenger load, the efficiency of the vehicle used (for transit or privately) and the fuel used. A quick glance  at this diagram shows that a bus with average occupancy emits three times more than a  4 passenger carpool in terms of emissions per passenger mile - and the two only become equivalent with a full bus. On the other hand, single occupant vehicle use produces more emissions than any transit alternative



Key Quotes:

“The environmental benefits of public transporta­tion vary based on the number of passengers per vehicle, the efficiency of the bus or train, and the type of fuel used“

“heavy rail transit, such as subways and metros.. produce 76% less in greenhouse gas emissions per passen­ger mile than an average single-occupancy vehicle.. Light rail systems produce 62% less and bus transit produces 33% less“

“The number of riders greatly impacts transit’s emissions savings..  bus transit, …with 28% of its seats occupied on average, emits an es­timated 33% lower greenhouse gas emissions per passenger mile than the average U.S. single occu­pancy vehicle…increases to 82% for a typical diesel transit bus when it is full with 40 pas­sengers “

“average 40-passenger diesel bus must carry a mini­mum of 7 passengers on board to be more efficient than the average single-occupancy vehicle“

“average heavy rail car .. at least 19% of seats full to exceed the efficiency of an automobile carrying an average passenger load.“

“new hybrid-electric buses consume 15% to 40% less fuel, and consequently produce 15% to 40% fewer car­bon dioxide emissions“

“Life cycle emissions include a full accounting of all emissions generated over the full life of a trans­portation system… in­creased estimates by as much as 70% for autos, 40% for buses, 150% for light rail, and 120% for heavy rail.“

“We’d be better off filling up cars on the road than we are running underutilized trains…This is why a reasonable accuracy in ridership forecasts matters”

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