How to turn gas guzzlers into green machines

How much gasoline could US citizens save by driving around in light-weight hybrid vehicles? Up to half what they currently use, say scientists at MIT.

The US consumes about 140 billion gallons of gasoline each year. A team of researchers led by John Heywood has completed a five-year assessment of what can be done to slash that and save fuel for the nation.

They looked at how gas and diesel engines, as well as hybrid electric cars and plug-in cars, are likely to evolve between now and 2035. They also assessed what can reasonably be expected from new fuels such as hydrogen and biofuels.

"Improvements" in cars in recent years have largely focused on increasing performance, driven by the demand for ever-larger and more powerful cars. As a result, no significant fuel consumption gains have been realised over the past 25 years, says the team.

They call for car manufacturers to focus efforts on improving fuel savings over performance.

Lighten the load

A seemingly simple way of reducing the amount of fuel used by cars without a big change in consumer preferences would be to produce lighter cars. Heywood's team estimate that the average US car 25 years from now could feasibly weigh between 20% and 35% less without compromising on security and convenience. This alone would cut fuel consumption by between 12% and 20%.

Looking to what types of cars could push petroleum cars off the roads in 15 to 30 years, the team see the greatest potential in hybrid electric and plug-in hybrid electric cars – with batteries that can be topped up from the grid.

Whereas current spark-ignition cars use on average 8.9 litres of gasoline to travel 100 kilometres, more efficient equivalents could consume just 5.5 litres by 2035, while hybrids and plug-in hybrids would consume 3.1 and 2.2 litres respectively.

The team calculate what this would mean in terms of carbon dioxide emissions. On average, current "conventional" cars in the US emit 277 grams of CO₂ per km travelled. In 2035, their equivalents could chuck out just 178g per km. Hybrids and plug-in hybrids, meanwhile, are projected to emit just 109g.

The price tag

There will be a price to pay though: the hybrids will cost between $2500 and $5900 more than their contemporary petrol-only equivalents. Heywood says the government may have to step in to help with the transition.

Despite the hurdles, he and his team estimate that by improving fuel efficiency over the next 15 years and bringing in "radically different" cars including hybrids and possibly fuel cell cars in the next 30, it should be possible to slash the amount of fuel guzzled by the gas-guzzling nation by 30% to 50% by 2035.

The team points out that the biggest change can come from the drivers themselves. "We have got to get out of the habit of thinking that we only need to focus on improving the technology, that we can invent our way out of this situation," says Heywood.

"Transitioning from our current situation onto a path with declining fuel consumption and emissions, even in the developed world, will take several decades – much longer than we had hoped or realised," he says. "We've got to start now."

Reference: On the road in 2035, 2008

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