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ES&T News
Environmental costs of shipping
Truck, train, or airplane—which one has the smallest environmental footprint when it comes to shipping? A new assessment published in ES&T (pp 7138–7144) examines the emissions released over the life cycles of several forms of freight transportation for long-distance deliveries in the U.S. Although rail transportation has the lowest emissions overall, all forms of transportation have phases in which emissions are much worse than in others. The researchers conclude that policy actions designed to reduce emissions from one phase of the life cycle can have unintended negative consequences, and they recommend policies that consider each phase carefully.
Cristiano Facanha of ICF International, a consulting firm specializing in transportation issues, and Arpad Horvath of the University of California Berkeley focused their life-cycle assessment (LCA) on greenhouse gases, particulate matter (PM), and other emissions from the U.S. freight transportation system. The researchers included data on emissions from building roads, tarmac, and rails, evaluated according to miles traveled by the ton.
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 assessment did not include the “short run” miles that are toted up by smaller trucks that might deliver goods to an airplane or rail yard for shipping. The researchers also excluded ship emissions, because those are limited mostly to freight on certain stretches of the Mississippi River or Great Lakes in the continental U.S.
Facanha and Horvath included tailpipe emissions generally considered for such studies: nitrogen oxides (NOx), SO2, PM less than 10 micrometers in diameter (PM10), carbon monoxide, and CO2. They combined two LCA methods to overcome the limits of each: process-based analysis, which translates inputs and outputs to a representative unit, and economic input–output analysis, which combines economic data with environmental impact. The authors found that CO2 and NOx emissions tend to be underestimated, by up to 38% for airplanes, but less so for trains and trucks. Facanha notes that “most of the time, rail is better than trucking—but you definitely have to qualify it.”
The authors’ policy models show that although NOx and SO2 may decline after restrictive regulations are in effect, PM10 might not. “We’re trying to raise the awareness of the decision makers” in both government and business, Horvath says, that “it’s not enough to focus on your fleet for delivering goods; it’s important to focus on other parts of the economy that service your goods, or delivery mechanisms.”
What Facanha and Horvath found may not be all that surprising, says Sonia Yeh of the Institute of Transportation Studies at the University of California Davis. And although the authors “used very stylish policy scenarios,” these model cases “beg more questions regarding the feasibility, costs, and the adequateness of current policies to regulate upstream emissions.”
