Jet-setters get a bad rap for their role in spewing greenhouse gases into the upper atmosphere, but a new study says that flying is really no worse for the environment than taking the train.

When most people think about air pollution and carbon emissions, they usually just consider just what’s coming from a vehicle’s exhaust pipe. But a new study in the journal Environmental Research Letters compares the impact of different transportation modes by taking into account everything from the steel in train tracks to the tires on aircraft landing gear.

A large aircraft emits about three times the greenhouse gases per passenger kilometer traveled than a train during operation. But if you consider the infrastructure that supports train and light rail travel, it effectively increases greenhouse gas emissions by a factor of 155 percent. A similar calculation for jets only increases the effective greenhouse gas emissions by 31 percent.

The two modes of transport are basically neck-and-neck, but on the U.S. east coast, where fossil fuels provide electricity for rail travel, trains end up being bigger greenhouse gas emitters than planes.

Trains also fared worse off when the study authors considered airborne pollutants like sulfur dioxide, which causes acid rain. The Boston Light Rail, for instance, emits more than seven times the amount of sulfur dioxide per passenger kilometer traveled than a typical large aircraft. That’s because today’s airplane fuels are low in sulfur, and power plants now dominate sulfur dioxide emissions.

The take-home message, says lead author Mikhail Chester at University of California, Berkeley, is not that eco-conscious travelers should shun rail lines in favor of planes. Instead, he says we should be looking at ways of reducing emissions in our infrastructure, by using, for instance, low carbon dioxide cement.

“We’ve done a lot by going at the tailpipe of the car,” says Chester, “That’s good thing, but we should start looking beyond the tailpipe.”

Image of train courtesy TroyMason via Flickr