UMTRI notes that despite the increase in sales of large vehicles, like the F-150, fuel economy levels continue to improve.

Automakers are maximizing the sweet spot in mix of sales, fuel economy and gas prices – bigger vehicles getting better gas mileage as fuel prices drop – and enjoying robust sales as a result.

Fuel economy trends continue to improve despite the continuing surge in the sales of light-duty trucks and sport utility vehicles. Meanwhile gasoline prices continue to decline as the end of the summer driving season looms.

The University of Michigan’s monthly measurement of the efficiency of new vehicles sold in the U.S. during July fell just shy of the all-time high, according to researchers at U-M’s Transportation Research Institute (UMTRI). 

The average fuel economy of cars, light trucks, vans and SUVs purchased last month was 25.6 mpg, just off the record-high of 25.7 mpg in May, but up from 25.5 mpg in June. Vehicle fuel economy is now up 5.5 mpg from October 2007, the first month of monitoring by UMTRI researchers Michael Sivak and Brandon Schoettle. The fuel-economy ratings come from the window stickers pasted on each car sold in the U.S.

The U-M index has been buffeted over the past year by the steady increase in truck and SUV sales but also reflects the tougher conservation measure imposed on automakers, which have required the broader use of fuel-saving technology.

In addition to average fuel economy, Sivak and Schoettle issued a monthly update of their national Eco-Driving Index (EDI), which estimates the average monthly emissions generated by an individual U.S. driver. The EDI takes into account both the fuel used per distance driven and the amount of driving – the latter relying on data that are published with a two-month lag.

The EDI stood at 0.79 (the lower the value, the better) during May, down from 0.80 in April. The record is 0.78, a mark set four times in the last year. The index currently shows emissions of greenhouse gases per driver of newly purchased vehicles are now down 21%, overall, since October 2007.

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The tougher fuel-economy standards are also getting credit with reducing demand for gasoline.

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The reduction in demand, coupled with the increase in production of petroleum from wells in the U.S., have helped blunt the impact of political upheavals in the Middle East, which could have driven up the price of oil. Over the past week, there has been intensified fighting in Iraq and in Libya. Both countries are key members of the Organization of Petroleum Exporting Countries or OPEC.

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Renewed tension on the Russian-Ukrainian border also has upset the stock market.

But gasoline prices have continued to drift lower, according to the Energy Information Agency. Gasoline prices were down by more than a penny per gallon from last week, the EIA said this week. Crude oil prices have dropped to less than $99 per barrel.