GREEN TRANSPORT

You worry a lot about the environment and do everything you can to reduce your carbon footprint -- the emissions of greenhouse gases that drive dangerous climate change. Think twice about 'green' transport, say scientists. So you always prefer to take the train or the bus rather than a plane, and avoid using a car whenever you can, faithful to the belief that this inflicts less harm to the planet. These are hidden or displaced emissions that ramp up the simple "tailpipe" tally, which is based on how much carbon is spewed out by the fossil fuels used to make a trip. In some circumstances, it could be more eco-friendly to drive into a city -- even in an SUV, rather than take a suburban train. "There's no overall solution that's the same all the time."

Boston has a metro system with high energy efficiency. The trouble is, 82 percent of the energy to drive it comes from dirty fossil fuels. San Francisco's local railway is less energy-efficient than Boston's. But it turns out to be rather greener, as only 49 percent of the electricity is derived from the fossils.

The paper points out that the "tailpipe" quotient does not include emissions that come from building transport infrastructure -- railways, airport terminals, roads and so on. These often unacknowledged factors add substantially to the global-warming burden. In fact, they 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.

A saloon (sedan) car may be responsible for less greenhouse gas per km travelled per person than a suburban train that is a quarter full, the researchers calculate. So getting a complete view of the ultimate environmental cost of the type of transport, over its entire lifespan, should help decision-makers to make smarter investments. For travelling distances up to, say, 1,000 kms (600 miles), we can ask questions as to whether it's better to invest in a long-distance railway, improving the air corridor or boosting car occupancy. Lets follow the safest mode of transport and save our environment.