Oct. 1, 2007 Trains are cleaner than planes and trucks for shipping goods with a few caveats, according to a new report.

A recent article in Environmental Science & Technology reports the findings of a new study that compared the environmental footprints of shipping via truck, train, and airplane.

Researchers from consulting firm ICF International and the University of California Berkeley focused their life-cycle assessment on greenhouse gases, particulate matter, and other emissions from the U.S. freight transportation system, including data on emissions from building roads, tarmac, and rails. They also looked at the emissions generated by the machinery used to load a plane or to lift a container onto a railcar as well as emissions from producing the fuel to keep the trains, trucks, and planes in motion.

The study finds that trains produce fewer emissions per mile traveled, but notes that efforts to reduce tailpipe emissions such as C02 and NOx, while successful, may overlook other harmful pollutants, such as particulate matter.

Another consideration: the miles traveled by goods shipped from a particular location to another vary depending on transportation method.

"It turns out that it's not as the crow flies," says UC Berkeley's Arpad Horvath, co-author of the study. The roads between points A and B can be a certain length, and rails may be 20%,30% more or less of those miles traveled." Air transportation, which often includes fuel-intensive stopovers at carrier hubs, may be even less direct. (The study further notes that while greenhouse gas emissions are generally underestimated for all shipping methods, airplane emissions may be underestimated by nearly 40%.)

"It's not enough to focus on your fleet for delivering goods," says Horvath. "It's important to focus on other parts of the economy that service your goods or delivery mechanisms."

Study co-author Cristiano Facanha of ICF concludes that "most of the time, rail is better than trucking but you definitely have to qualify it."