Rough roads impose a hidden tax on motorists in wear and tear, depreciation and higher fuel use that can add 20 cents a mile over the cost of driving on smooth surfaces, says Lynne Irwin, Cornell associate professor of highway engineering.

"We pay about 50 cents a gallon in taxes at the pump, and another 50 cents a gallon or more when the roads are rough," says Irwin. When roads are smooth, motorist costs to operate their vehicles are, on average, about 30 cents per mile, not counting the taxes, he says. That cost goes up to 40 cents, or even 50 cents per mile, depending on road roughness. "Fortunately only a small portion of our driving is on rough roads," Irwin says.

The extra costs to motorists due to rough roads can be saved if roads were repaved before they begin to break up. To that end, Irwin works with devices called falling weight deflectometers (FWDs), specialized computers in a truck, which evaluate the structural integrity of pavement and predict when cracks, potholes and ruts will develop.

"Bad roads are like a sore foot. You only think about a sore foot when it hurts. You are not aware that it is not sore. The same is true of rough roads," says Irwin, who has been spearheading groundbreaking -- or rather road-preserving -- research for more than 25 years to keep roads smooth. Irwin is director of the Cornell Local Roads Program, which does research on roads and provides technical assistance and training for local government highway officials and employees in 1,608 municipalities in New York state.

Would the cost of keeping the roads in good condition save motorists enough to warrant repairing the roads before they break up? Federal and state governments and local authorities, he says, fail to consider road-user costs when deciding whether to spend tax money to fix the roads.

If highway departments repaired roads at the right time, it could cost taxpayers much less to drive on them, Irwin says.

"We should be managing our public roads to minimize the total cost -- consumer cost plus highway agency cost, which is taxpayer money anyway. Deteriorating roads cost less to repair if they are rehabilitated before they are badly broken up, and they cost motorists less to drive on," Irwin says.

To facilitate the use of FWDs, Irwin has been using and testing the devices for almost 25 years. An FWD works by dropping a weight onto the pavement at a given force, and sensors around the weight record the subsequent deflections. By measuring the deflections on the surface of the pavement at various points over a distance of 6 feet from point of contact, experts can predict when the road will deteriorate into cracks and potholes.

Irwin was the first to bring an FWD to the United States in 1982 (there are now some 225 FWDs throughout the country) and to develop software that could be used to make sense of the device's data. He also is participating in a 20-year study through 2009 using FWDs at 2,000 road sites. He is now concluding a national study to update software and calibration procedures to improve the accuracy of the devices.

"The work will allow highway agencies to repair roads before drivers see physical evidence of the deterioration," says Irwin. And that, he says, would save both agencies and motorists significant costs, especially in this age of soaring fuel costs.