A team from the University of Tennessee and the National Renewable Energy Laboratory (NREL) has the fuel savings due to fuel economy improvements over the past 43 years amount to approximately two trillion gallons of gasoline.

They further estimated that roughly one-fifth of the savings can be attributed to gasoline price increases over the period and four-fifths to fuel economy and greenhouse gas (GHG) standards. Their paper is published in the journal Energy Policy.

Estimated attribution of fuel savings due to fuel economy improvements to light-duty vehicles since 1975. Greene et al.

Since 1975, the test-cycle fuel economy of light-duty vehicles (passenger cars and light trucks) sold in the U.S. has almost doubled. Also since 1975, light-duty vehicle travel increased by 134% while fuel use increased by only 37%. Fuel economy improvements on laboratory tests gradually became real improvements on the road as newer, more efficient vehicles were added to the vehicle population and older less efficient ones were retired. Fleet-wide fuel economy gains produced large fuel savings. However, quantifying the fuel savings is challenging due to the mapping from test-cycle to on-road fuel economy and the dynamic response of driving behavior to changes in fuel economy (i.e. the rebound effect).

We address both of these challenges and estimate that cumulative fuel savings reached 2 trillion gallons by the end of last year, which exceeds the total consumption of all U.S. light-duty vehicles over the past 15 years. These cumulative fuel savings translate into fuel cost savings of $4.9 trillion and a reduction of 17 billion tons of CO₂.

—Greene et al.

The authors used a three-step method:

• First, they demonstrated that energy efficiency improvements to new vehicles on the tests used to certify compliance with fuel economy standards translated into approximately proportional improvements on the road. This step provided a limited validation of both the EPA’s new car fuel economy estimates and the FHWA’s total on-road light-duty vehicle fuel economy estimates.

• Second, they estimated fuel savings using the FHWA data on vehicle miles, fuel use and miles per gallon (mpg). Two indirect effects were considered. First, had fuel economy not improved, the higher level of U.S. gasoline demand would have put upward pressure on world oil prices. Second, the full effects of fuel economy improvements are conditional on how consumers value fuel economy in their vehicle purchase decisions and whether the improvements made have been cost effective or not.

  They added indirect rebound effects via income and world oil prices to the calculations because, in principle these could have non-trivial impacts on fuel savings. To acknowledge the uncertainty about such effects, they conducted a sensitivity analysis.

• Third, they used estimates of the fuel price elasticity of light-duty vehicle fuel economy and a lagged adjustment model to estimate the effects of gasoline prices on mpg from 1975 to 2018 in the absence of fuel economy and GHG regulations. They used this to approximately attribute the total savings due to fuel economy improvements to changes in the price of gasoline versus regulatory standards and other factors. Again, because of the uncertainties in the attribution they conducted a sensitivity analysis.

Resources

• David L. Greene, Charles B. Sims, Matteo Muratori (2020) “Two trillion gallons: Fuel savings from fuel economy improvements to US light-duty vehicles, 1975–2018,” Energy Policy, Volume 142, 111517 doi: 10.1016/j.enpol.2020.111517