When Driving is Better Than Flying

European researchers say driving a long distance solo has the same environmental impact as making the trip by plane. But car pooling with two or more others is better than taking a train, and traveling by diesel-powered bus is the "cleanest" option.

Next-generation piston-powered cars will have such low emission levels for most pollutants that their climate impact will be "completed dominated" by their carbon dioxide output, according to the trio of Austrian and Norwegian scientists.

The group reports its findings in the current issue of the American Chemical Society's Environmental Science & Technology.

The team calculated environmental impact for trips of 500-1,000 km (310-621 miles). They included emissions of aerosols, oxides of nitrogen, carbon monoxide, CO₂ and volatile organic compounds. For planes, they estimated the short-term impact of aviation-induced cirrus clouds and contrails. Their results indicate ranges for each mode of transportation that cover occupancy and types of vehicle in each category.

Their analysis concludes that aircraft have the highest specific environmental impact regardless of passenger count.

Even fully loaded planes contribute an average 188 grams of CO₂ per passenger-kilometer, according to the team. That compares with approximate averages of 55 for a fully loaded gasoline car, 35 for a diesel car, 25 for a train and 20 for a diesel bus.

The team includes Jens Borken-Keenfeld from the International Institute for Applied Systems Analysis in Laxenburg, Austria; Jan Fuglestved from the Center for International Climate and Environmental Research in Oslo, Norway; and Terje Berntsen from the University of Oslo's Dept. of Geosciences.