The average fuel economy in newly sold vehicles in the United States remained unchanged in March, according to researchers at the University of Michigan Transportation Research Institute.

The typical new vehicle sold during the month had a window sticker fuel economy of 25.3 miles per gallon, the same average as February. The March average was up 0.1 miles per gallon from January, but down 0.1 miles per gallon compared to March 2015.

The average was also half a mile per gallon below a peak set in August 2014, when the typical new vehicle sold in the U.S. had a fuel economy of 25.8 miles per gallon. However, it was up 5.2 miles per gallon from the start of monitoring in October 2007, when the average vehicle got only 20.1 miles per gallon.

UMTRI research professor Michael Sivak and project manager Brandon Schoettle create a sales-weighted figure for new vehicle fuel economy each month. This figure is calculated using monthly sales data as well as the combined city and highway fuel economy figures for models as listed in the Environmental Protection Agency's Fuel Economy Guide.

The average fuel economy in new vehicles has remained relatively unchanged since the August 2014 high, varying between 25 miles per gallon and 25.5 miles per gallon. Sivak and Schoettle have attributed this trend to lower gas prices and higher sales of less efficient vehicles, such as trucks and SUVs.

In addition to the fuel economy data, the researchers issue a monthly update of their Eco-Driving Index. This figure estimates the average monthly emissions generated by an individual American driver, based on the distance driven and the fuel used for this travel. The figure is updated on a two-month delay since it is based on travel data from the Federal Highway Administration, which publishes on this timeline.

The Eco-Driving Index for January was 0.84, indicating that the average driver of a new vehicle produced emissions levels that were 16 percent lower than those of October 2007 drivers. The figure was up from 0.83 in December and a record low of 0.78 in August 2014.

The distance traveled in January was 4 percent higher than in October 2007. However, the fuel used per distance driven was 19 percent below the fuel consumption levels in that month.