Used Class 8 truck sales in May fell 11% compared with the previous month, to 2,496 units, according to the latest report from ACT Research.

Sales are still up 3% compared with May 2014, but the used truck market has seen substantial sales declines for the past few months.

“Volume softening can be seen in the retail and wholesale markets, with month over month declines of 12% and 14%, respectively,” said Steve Tam, vice president of commercial vehicle sector at ACT. “Our guidance for full year 2015 sales remains unchanged.”

Average prices have flattened but are overall up 8% so far this year, which is in line with ACT’s expectation of 5% to 10% growth in 2014. Transactions from auctions saw an increase in May of 9% over the previous month and are 8% higher than this time a year ago.