For the environmentally-conscious traveler, choosing the best possible mode of transportation has thus far been pretty easy. One can simply compare the greenhouse gas emissions of a car versus a train or a plane. But researchers from UC Berkeley’s Department of Civil and Environmental Engineering have developed a new framework for calculating the full environmental costs of travel, taking the entire life-cycle of the transportation mode into consideration and making travelers’ decisions smarter, although much more complex.

The new framework out of Berkeley, published yesterday in IOP Publishing’s Environmental Research Letters, looks not only at end-result emissions, but also at all the environmental impacts weathered along the way. These impacts include energy source, type of power plant, construction, and more. For example, the Berkeley team followed the transportation life cycle of a light railway system in Boston, and found it had a much larger carbon footprint than a comparable system in San Francisco. This emissions hike is due to Boston’s energy supply, which draws 82 percent of its power from fossil-fuels, compared with 49 percent in San Francisco.

The Berkeley framework also takes into account the number of travelers on any given vehicle. For example, a half-full Boston light rail is only as efficient as a mid-size aircraft at 38 percent capacity.

The full-cycle method is particularly interesting now, as governments worldwide weigh various renewable energy sources in efforts to address the climate crisis. Nuclear may be “clean” to burn, but what is the environmental impact of nuclear waste, and what about mining and milling uranium, let alone building new plants? If your car runs on corn-based ethanol, how much chemical fertilizer was used and what is the environmental cost of the plant that produces the ethanol? (Search for "ethanol" on for a stream of information and debate.) The framework provides a new way for us to make ever smarter decisions, although it does take some of the fun out of previously benign activities. The next time I take a walk in the woods, I’ll be thinking about my sneakers, what they’re made of, and where they came from.