Fuel efficiency may not lead to lower fuel bills

Nearly 20 percent of the energy-saving benefits of fuel-efficient cars are eroded because people end up driving them more, according to a study.

Researchers at University of Sussex used data from 1970 to 2011 to find this long-term "rebound effect" among British car drivers.

"Improvements in fuel efficiency should lead to reductions in fuel consumption. But since improved fuel efficiency makes driving cheaper, some of the potential fuel savings are 'taken back' through increased driving," said Lee Stapleton, a researcher at University of Sussex's Centre on Innovation and Energy Demand.

"We call this the rebound effect and it is well-documented in other sectors. For instance, we know that insulation of housing encourages people to enjoy warmer homes, rather than taking all the benefits in the form of lower bills," Stapleton added.

In order to measure the rebound effect, the Sussex researchers tested more than a hundred different models, each focusing on different variables.

Their lowest estimate of the rebound effect came out at 9 percent and their highest as 36 percent. The average was 20 percent.

The findings were published in the February issue of the journal Energy Economics.