Light-duty (car or small truck) vehicles are only one of many modes of personal transportation. Greenhouse gas emissions from these modes vary widely. A person on a bicycle emits about 2.3 grams of carbon per kilometer, and a person walking or running emits 6.3 grams per kilometer; these modes are the ultimate in biofuel conversion. At the other extreme, a commuter helicopter emits carbon at a rate of 180.5 grams per kilometer per passenger.
A central factor in transportation efficiency is passenger occupancy. Except for cycling, walking, or running, the incremental energy required per additional passenger is small for most modes of transportation. Therefore, doubling passenger occupancy nearly halves the effective greenhouse gas emissions per distance traveled.
Private and public modes of transportation. Travel (1012 passenger-km) in the United States and Europe via private ground vehicles, public air carriers, or public ground transport (buses, railroads, vans, or ferries). [After Eurostat 2003, 2006; American Public Transportation Association 2007; Bureau of Transportation Statistics 2008.]
The vast majority of travel in the United States and Europe is via private vehicles, which include cars, small trucks, SUVs, and motorcycles. Attempts to encourage carpooling through special highway lanes and toll-free passage over bridges have met with only marginal success. In fact, the percentage of people who carpool to work in the United States has not changed significantly over the past eighteen years. The percentage of those who walk or cycle to work has also not changed.
Number of people (millions) in the United States who travel to work via different modes of transportation. “Public transport” denotes ground transport. “Other” includes those who walk and bicycle. After Bureau of Transportation Statistics 2008.
By contrast, ridership on public ground transport has expanded significantly from a low point in the 1970s. This includes a 50% increase in travel via rail and other forms of public ground transport except for buses. Public air travel—except for the period after the airplane crashes on September 11, 2001—has also risen steadily. Nevertheless, travel in vehicles carrying only one passenger is still gaining ground on all other forms of transportation.
Freight is more sensitive to economic market forces than personal transportation. For example, no one cares whether their packages arrive in an elegant limousine or a big, brown, boxy van as long as they are delivered quickly and intact. The shipping industry (air, sea, road, and rail) thus responds more directly to rising petroleum costs than does personal transportation. For instance, the shipping industry quickly adopted technologies that improve fuel efficiency such as diesel, hybrid diesel-electric, compressed natural gas, and aerodynamic cowlings for truck cabs.
This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.
©2010 Sinauer Associates and UC Regents