Sales of used Class 8 commercial vehicles were up 55 percent in August compared to the prior year on a "same dealer" basis, according to ACT Research Co.

In addition, the average price paid for a used Class 8 truck is rising, reported ACT, which offers commercial vehicle industry data, market analysis and forecasting services. In August, the average price of a used Class 8 vehicle sold in a retail setting (excludes auctions and wholesale transactions) broke the $40,000 barrier for the first time since February of 2009, ACT reported in the latest release of its "State of the Industry: U.S. Classes 3-8 Used Trucks."

"While unit sales are up year-over-year, recent months have seen flat to slightly downward sales volume as dealers have voiced concerns over a shortage of late-model inventory," said Steve Tam, vice president-commercial vehicle sector with ACT. "As in most cases when supply tightens, prices go up."

ACT Used Truck database participants report approximately 2,500 transactions per month. ACT estimates that approximately 10 percent of used Class 8 transactions are included in the database.