The average fuel economy number for new, light duty vehicles sold in the US reached an all-time high of 24.1 miles per gallon in October, up from 23.8 mpg the previous month, according to a report released by the University of Michigan's Transportation Research Institute.

That equals a 4.0-mpg increase, or 20 percent, since October 2007, when researchers Michael Sivak and Brandon Schoettle began collecting the data. The number comes from sales-weighted fuel economy calculated from monthly sales of individual models and city-highway fuel economy ratings from the EPA Fuel Economy Guide. It corresponds to a 17-percent reduction in fuel consumption per distance driven, Sivak said in a statement.

The report also updated its national Eco-Driving Index, which estimates monthly greenhouse gas emissions per individual driver in the US. In August, the index reached .81, unchanged from July, but down 19 percent from October 2007. The number is based on vehicle fuel economy and distance driven and has a two-month lag from available published data. You can view the fuel economy graphs and data and the Eco-Driving Index.

US corporate average fuel economy is supposed to reach 35.5 mg by model year 2015 and 54.5 mpg by model year 2025, according to federal standards. The fuel economy numbers are increasing each month, but need to increase proportionally for the mandates to be reached.