MC LEAN, Va. -- The U.S. Environmental Protection Agency badly underestimated how much diesel engine emissions rules -- from 2004 through 2010 -- would impact truck prices, according to a new study.

Not only did the increasingly stricter exhaust-emissions regulations turn off truck buyers, but the resistance was counterproductive to the EPA goal of cutting NOx and diesel particulate emissions when truck owners held onto their older trucks.

"This study shows what can happen when a regulatory proposal seeks to set mandates far in the future, and based on far-in-advance predictions," said Dave Westcott, vice chairman of the National Automobile Dealers Association.

"Importantly, it documents the real world market disruptions that can occur as a result."

The same environmental regulations that impacted over-the-road truck diesel engines from 2004-10 also were applicable to the power plants that went into motorcoaches during the period.

The trucking study says the EPA underestimated regulation compliance costs by two to five times, with the new engines adding thousands to truck prices and leading to the unintended consequence of depressed new truck sales and increased truck emissions.

U.S. retail sales of heavy-duty trucks neared 500,000 in 2005, but fell to around 200,000 in 2009, the study says.

"Truck sales literally fell off the cliff," said Dick Witcher, chairman of American Truck Dealers and owner of an International Truck dealership. "Instead of buying new trucks, many operators chose to hold onto their older trucks longer, and willingly accepted higher operational costs."

Truck owners purchase decisions appear to have been driven by two factors, the study said inflated costs of new trucks that far exceeded EPA predictions and the unreliability of the new technology being rolled out to meet 2004, 2007 and 2010 standards.

EPA estimated that from 2004 through 2010 compliance costs would add an average of $5,136 to truck prices. Surcharges from OEMs, however, averaged more than $21,440 for popular truck models, according to the study.

A trucking industry legislative affairs specialist pointed out that the higher truck prices and unreliability of the new technology had been particularly burdensome to small carriers.

Smaller trucking businesses, especially those companies that do not receive volume discounts afforded larger motor carriers, absorb every environmental cost, the lobbyist pointed out.