PARIS (AFP) – Taking public transport may not be as green as you think, says a new US study. Its authors point out an array of factors that are often unknown to the public. 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, for instance, it could be more eco-friendly to drive into a city -- even in an SUV, the bete noire of green groups -- rather than take a suburban train. It depends on seat occupancy and the underlying carbon cost of the mode of transport.
For example, 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.
By comparison, 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 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 -- nor the emissions that come from maintaining this infrastructure over its operational lifetime.
These often-unacknowledged factors add substantially to the global-warming burden.
And another big variable that may be overlooked in green thinking is seat occupancy.
A saloon (sedan) car or even a 4x4 that is fully occupied may be responsible for less greenhouse gas per kilometer travelled per person than a suburban train that is a quarter full, the researchers calculate.
I’m convinced; I’m selling my smart car and buying one of these:
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