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Environment & Climate Change

Greenhouse gas emissions up from transportation sector

Chart showing greenhouse gas emissions over time.
Michael Sivak and Brandon Schoettle
University of Michigan
U.S. greenhouse gas emissions, 1990-2014.

Industries in the U.S. have made some progress cutting greenhouse gas emissions over the past couple of decades. But emissions are up from the transportation sector. This matters because transportation is the nation’s second-largest source of the emissions that are causing climate change.

Brandon Schoettle is the project manager for Sustainable Worldwide Transportation with the University of Michigan Transportation Research Institute. He and his colleague Michael Sivak analyzed emissions data from the EPA from 1990 to 2014.

“The main reason emissions are up in the transportation sector is due to increased emissions from medium and heavy duty trucking, and that of course, we think is mostly due to increases in the actual use of medium and heavy trucks, things like construction, transporting goods and cargo around the United States," says Schoettle. "Increases over the period we looked at in the actual mileage and cargo hauling in these industries have been the main reason that their emissions are up. Most other parts that make up the transportation sector have stayed relatively flat during that time."

More cars on the road

He says even though there’s been more than a 30% increase in the number of light-duty vehicles during the 1990-2014 time period, the emissions from light duty vehicles have stayed about the same.

"Vehicles have just been getting more efficient during that time. Recently we’ve hit some records in terms of new vehicle fuel economy," he says. "Especially over the past 10 or 15 years, there’s been major jumps in new vehicle fuel efficiency. So those gains, even though we’ve been also gaining quite a few vehicles, have led to a sort of stable performance in terms of emissions."

So what do we do about those medium- and heavy-duty trucks?

Schoettle says that's tricky.

"For cargo, it’s a little different, they traditionally get what we would generally think of as pretty poor fuel economy, five, six, seven miles per gallon. But of course they’re hauling tens of thousands of pounds of cargo around," he says. "So they’ve been increasing their cargo efficiency significantly during the same period we looked at, but the increase in just cargo operations moving around the country has led to the increase there."

He says his team is working on a study due out later this summer "where we’re looking at fleets and asking them to tell us what they think some of the future technologies are in that category, so they’re doing just as much work as other parts of the transportation sector to try to figure out ways to increase their efficiency too."