The price for used sleeper tractors rose in July, both on a month-to-month and year-over-year basis, reports the American Truck Dealers Commercial Truck Guide.

The guide, put out by ATD and parent group, the National Automobile Dealers Association, determined that on average, sleeper tractors sold in July for $50,067 with 557,364 miles and were 75 months old. This price is up 1.7% over June and 5.2% over July 2011.

July was only the second time in the past four years in which average price broke the $50,000 barrier.

A relatively flat first half of 2012 combined with mixed economic data led ATD/NADA to expect a mild pullback in pricing.

"If there had been any relaxation in demand for sleeper tractors earlier in the year, that relaxation turned out to be temporary and inconsequential," said Chris Visser, senior analyst with the ATD/NADA Commercial Truck Guide. "We've said repeatedly that the supply of low- to average-mileage used trucks will support high pricing, and July's results confirm this position."