The FTA has a new (January) report on carbon footprints of various transit modes, based on 2008 data. For electric transit, the authors use estimates based on the composition of that region’s power grid. Here are the locally relevant figures:

System lbs. CO2 per passenger mile Washington State Ferries 2.123 Seattle Streetcar 1.301 Avg. U.S. SOV 0.964 Metro Diesels 0.452 [Tacoma] Link 0.411 Metro trolleys 0.388 Sounder 0.369 ST Express 0.327 King Co. Vanpools 0.246 Snohomish Co. Vanpools 0.239 Pierce Co. Vanpools 0.228 Seattle Center Monorail 0.190

For comparison, the Portland MAX, a more mature system, comes in at 0.213. The national champion is Maryland’s MARC commuter rail at 0.013. Of large systems, BART (0.085) is very efficient with particularly clean energy.

Thoughts below the jump.

What’s missing here is the extent to which certain transportation types encourage density and walking, thus reducing passenger miles and overall carbon impacts. That’s difficult to measure but important to remember.

Considering Link’s partial implementation and relatively undeveloped corridor, it is doing pretty well and will probably be in the ballpark of MAX when built out. [This 2008 data of course refers to Tacoma Link. No more late night edits!]

For some of these modes, the marginal cost of a new rider is zero; those modes will be better at sustainably accommodating growth.

King County’s vanpool system is second in size in the nation (!), behind only Utah Transit Authority. It serves 6.2% of all vanpool passenger miles in the nation.

Via Huy Le of Green Growth Cascadia.