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Public Transport Systems Not Always A Greener Solution

June 8, 2009

A new study from researchers at the University of California at Davis has found some evidence that dispels conventional wisdom about green transport.

While most environmentally conscious people would be quick to assume that urban public transport systems are safer in regards to carbon emissions, environmental engineers Mikhail Chester and Arpad Horvath found that in some cases, people would be better off traveling through town in a gas-guzzling, high emission SUV.

Chester and Horvath told AFP that there are many factors that rarely go into public consideration.

“We are encouraging people to look at not the average ranking of modes, because there is a different basket of configurations that determine the outcome,” said Chester.

“There’s no overall solution that’s the same all the time.”

Researchers noted that the overall efficiency of a mode of public transport often depends on the location. For example, the metro system in Boston has high energy efficiency, but 82 percent of its energy comes from fossil fuels.

In contrast, San Francisco’s rail system is less energy-efficient than Boston’s system, but it is more economically friendly because just 49 percent of its energy is derived from fossil fuels.

Their report shows how “tailpipe” estimates fail to add emissions involved in building transport infrastructure. These overlooked figures add 63 percent to the “tailpipe” emissions of a car, 31 percent to those of a plane, and 55 percent to those of a train, said Chester and Horvath.

Additionally, researchers said that another key factor is seat occupancy.

In some cases a SUV that is fully occupied may be more efficient than a public train that is only a quarter full, they said.

“Government policy has historically relied on energy and emission analysis of automobiles, buses, trains and aircraft at their tailpipe, ignoring vehicle production and maintenance, infrastructure provision and fuel production requirements to support these modes,” researchers found.

The report is published in Environmental Research Letters, a publication of Britain’s Institute of Physics.

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UC Davis

Britain’s Institute of Physics




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