In 1923, the average fuel economy of all vehicles on U.S. roads and highways was 14 miles per gallon (mpg). Fifty years later that fuel economy rating had dropped to 11.9 mpg. Since then, fuel economy has risen slowly to a rating of 17.9 mpg for all vehicles in the U.S. fleet.

Including just cars and light trucks and beginning in 1965, all light vehicles saw fuel economy drop from 13.5 mpg to 12.9 mpg in 1973, the year of the first oil embargo. Fuel economy rose to 19.6 mpg by 1991 but has since slowed and now stands at 22 mpg for all cars and light trucks on U.S. roads.

The data were reported this week by Michael Sivak and Brandon Schoettle of the University of Michigan Transportation Research Institute. The report also includes data for medium- and heavy-duty trucks.

The entire fleet of light-duty vehicles (passenger cars, pickups, SUVs, and crossovers) in the U.S. at the end of 2016 totaled 264 million registered vehicles. The average age of a light-duty vehicle is currently 11.6 years. Total new car sales in the U.S. last year reached 17.6 million light-duty vehicles, just 7.6% of the total number of vehicles on U.S. roads and highways.

If new car sales remained at 2016 levels it would take 15 years to replace all the light vehicles currently on U.S. roads.

The University of Michigan report also notes prior research indicating that improving fuel economy is more beneficial at the lower end of the fuel economy distribution curve. For example, an improvement in fuel economy from 15 mpg to 16 mpg reduces fuel consumption by 50 gallons for every 12,000 miles driven. Improving fuel economy from 40 mpg to 41 mpg results in fuel consumption savings of just 7 gallons in 12,000 miles of driving.

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