Think twice about 'green' transport, say scientists

Yahoo News 7 Jun 09;

PARIS (AFP) – 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.

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.

Well, there could be a nasty surprise in store for you, for taking public transport may not be as green as you automatically 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.

Environmental engineers Mikhail Chester and Arpad Horvath at the University of California at Davis say that when these costs are included, a more complex and challenging picture emerges.

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.

"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," Chester told AFP in a phone interview.

"There's no overall solution that's the same all the time."

The pair give an example of how the use of oil, gas or coal to generate electricity to power trains can skew the picture.

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.

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.

And another big variable that may be overlooked in green thinking is seat occupancy.

A saloon (sedan) car or even an 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.

"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," they say.

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 kilometres (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," said Chester.

The paper appears in Environmental Research Letters, a publication of Britain's Institute of Physics.

The calculations are based on US technology and lifestyles.

It used 2005 models of the Toyota Camry saloon, Chevrolet Trailblazer SUV and Ford F-150 to calibrate automobile performance; the light transit systems in the San Francisco Bay Area and Boston as the models for the metro and commuter lines; and the Embraer 145, Boeing 737 and Boeing 747 as the benchmarks for short-, medium- and long-haul aircraft.

Train can be worse for climate than plane
Catherine Brahic, New Scientist 8 Jun 09;

True or false: taking the commuter train across Boston results in lower greenhouse gas emissions than travelling the same distance in a jumbo jet. Perhaps surprisingly, the answer is false.

A new study compares the "full life-cycle" emissions generated by 11 different modes of transportation in the US. Unlike previous studies on transport emissions, this one looks beyond what is emitted by different types of car, train, bus or plane while their engines are running and includes emissions from building and maintaining the vehicles and their infrastructure, as well as generating the fuel to run them.

Including these additional sources of pollution more than doubles the greenhouse gas emissions of train travel. The emissions generated by car travel increase by nearly one third when manufacturing and infrastructure are taken into account. In comparison to cars on roads and trains on tracks, air travel requires little infrastructure. As a result, full life-cycle emissions are between 10 and 20 per cent higher than "tailpipe" emissions.

Mikhail Chester and Arpad Horvath of the University of California, Berkeley, included in their calculations data on the "life expectancy" of each component of each mode of transportation, such as the tracks used by a train and the airports used by aircraft.

They calculated the total "travel kilometres" each component allows and how many tonnes of greenhouse gases were emitted to build and maintain each component. This allowed them to calculate the component's emissions per kilometre travelled, for each mode of transport per kilometre for each traveller on board.
Empty seats

Cars emitted more than any other form of transport with the notable exception of off-peak buses, which often carry few passengers. Passengers on the Boston light rail, an electric commuter train, were found to emit as much or marginally more than those on mid-size and large aircraft. This is because 82 per cent of electricity in Massachusetts is generated by burning fossil fuels.

The researchers found that travelling 1 kilometre on a nearly empty bus during off-peak hours emits eight times more per person than taking the same bus at rush hour – suggesting peak-time commuters may suffer, but they do less harm to the environment.

The occupation level of a vehicle is an important but often-overlooked factor, says Chester. "Although mass transit is often touted as more energy efficient than cars, this is not always the case." Buses turned out to be the most sensitive to how full they were – those with only five passengers were less efficient than cars; even large SUVs and pick-up trucks.
Clearer view

The results make it easy to target attempts to cut emissions and could change how politicians think about measures to improve transportation, say the researchers.

The life-cycle emissions generated by cars, buses and aircraft are dominated by tailpipe emissions pumped out in day-to-day running of their engines. Hence, the best way to reduce emissions from these modes of transportation would be to increase fuel efficiency and push for renewable fuels.

Crisscrossing the US with a rail network, however, creates a different problem. More than half of the life-cycle emissions from rail come not from the engines' exhausts, but infrastructure development, such as station building and track laying, and providing power to stations, lit parking lots and escalators

Any government considering expanding its rail network should take into account the emissions it will generate in doing so, Chester says. Setting up a public transportation system that only a small proportion of the population uses could generate more emissions than it cuts, he adds – especially if trains and buses are not well connected.

"New rail systems should serve as links to other transit modes, as is often the case in Europe and Japan," he says. "We should avoid building rail systems that are disconnected from major population areas and require car trips and parking to access."

Transport studies expert Abigail Bristow of Loughbourough University, UK, says the paper is valuable because it attempts to compare transport on equal terms. "The conclusion that rail emissions are best reduced by reducing the use of concrete in station construction is a nicely different perspective that a purely transport oriented analysis might have missed," she says.

Journal reference: Environmental Research Letters (DOI: 10.1088/1748-9326/4/2/024008)