"We saw an increase in fuel economy in both fleets of 1.4%, which is a big deal," Flanigan reported. "And based on current fuel costs (estimated by Flanigan at $4 per gallon for example purposes) and equipment costs of about $1,500 per tractor-trailer unit, the ROI comes in under one year." The DOT conducted the tests between April 2008 and December 2010 using two regional fleets. Through the test period, the two fleets accumulated more than 7 million road miles, used 1.15 million gallons of diesel, and replaced 440 tires due to wear. Another 115 tires were replaced due to damage. Despite the different service conditions, Flanigan noted, both fleets showed an equal reduction in fuel consumption at 1.4%. Steer tire tread wear for the fuel hauling/delivery fleet improved by 5/32nds of an inch per million miles, while trailer axle tread wear improved 2/32nds. Tread wear on the drive tires for that fleet, however, soared to almost 30/32nds of an inch, Flanigan reported.