North Carolina's weak laws regulating overweight trucks and poor enforcement by the state Highway Patrol show up every year in a place you might not have considered: Your taxes.

Every day, at least 100,000 medium-sized and big trucks are on the move in North Carolina. One legal truck, weighing 80,000 pounds, does at least as much damage to roads as 5,000 cars, experts say. And damage from heavier trucks -- running illegally or approved by special state laws -- goes up dramatically.

No one can say precisely how much heavier trucks cost taxpayers in additional repairs, but Len A. Sanderson, the state highway administrator, says there's a direct connection.

"More weight, more tearing up, the more maintenance money you need," he said.

How many trucks might be overweight would only be a guess were it not for an obscure unit in the state Department of Transportation that has been gathering data on truck weight for a federal pavement study.

The data include records of about 440,000 tractor-trailers weighed in 2003 by equipment buried in the pavement at 16 locations in 12 counties. According to an analysis by The News & Observer, one truck in 12 weighed more than 80,000 pounds, the interstate maximum.

More significant: In the wee hours of the morning, trucks are three times as likely to be overweight as trucks moving during the day, when weigh stations are more likely to be open and when weight enforcement officers are more likely to be on patrol.

DOT told the Federal Highway Administration that it would share that data with officers responsible for catching overweight trucks, but it hasn't. Kent L. Taylor, state traffic survey engineer, said the data could generate better decisions on what time of day to have enforcement officers working.

"We just haven't had the staffing to do that," he said about sharing the data.

The state spends about $615 million a year to maintain its highway system, Sanderson said. It needs to be spending $1 billion, he said, and part of that can be blamed on overweight trucks.

The money for maintenance and other highway needs comes primarily from the state and federal taxes on fuels. The total tax on a gallon of diesel, which trucks use, is 51.25 cents. The tax on gasoline, used by most cars, vans, pickups and SUVs, is 45.25 cents per gallon. Still, a federal study says big trucks don't pay their fair share because of the damage they cause.

Legislators have not raised overweight truck fines in 24 years. Instead, for some of the most frequent violators, they have upped the legal weight limits and cut the penalties in half. In effect, after adjusting for inflation, many overweight trucks are fined a fourth as much as they were in 1981, the last time penalties were raised.

Heavy load, high cost

Judith Corley-Lay, the state's top pavement management engineer, says she has been asked often by legislators how much another increase in weight limits would cost in damage.

"Every single year I get called in to answer some various nuance of the question," she said. "If we increase the load limit to X, what is the dollar cost of that increase? And it's a very frustrating question because it's very complicated technically."

But Corley-Lay has calculated what would happen -- and how much it would cost -- in a hypothetical situation. She said if truck weights were increased 10 percent on interstate highways, pavement designed to have a 20-year life would wear out in seven. And maintenance would increase by $129 million a year.

But interstates account for only 1,019 miles of the state's 78,615-mile highway system. So the cost of a 10 percent increase on the state's primary and secondary roads would substantially increase Corley-Lay's damage estimate.

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