By April Castro, Published September 11 2007
In interviews with The Associated Press, some experts warned that the practice of issuing state permits that allow trucks to exceed the usual weight limits can weaken steel and concrete, something that investigators say may have contributed to the Minneapolis bridge collapse Aug. 1 that killed 13 people.
“We talk about this all the time, and the fear that we have is that we’re going to have the same sort of disaster here that happened in Minnesota,” said Don Lee, executive director of the Texas Conference of Urban Counties.
In 2000, Milwaukee’s Hoan Bridge collapsed when steel girders cracked. Several factors were blamed for the collapse, including a significant number of heavy trucks, some over the normal weight limit, that routinely traveled over the bridge.
The weight limit for nearly all interstate highways is 40 tons. According to a government study, one 40-ton truck does as much damage to the road as 9,600 cars.
But permits frequently allow vehicles to exceed that amount by two tons in Texas and sometimes as much as 85 tons in Nevada. Some states grant one-time permits that allow trucks to be considerably heavier.
Around the country, many transportation officials dismiss such fears as overblown and say roads and bridges are safe, though some express concern that not enough is being spent to repair the damage done by extra-heavy trucks.
As for why they issue overweight-load permits, many state officials said they have no choice – they are simply carrying out the laws as passed by the legislature. Critics of those laws say they are often written to benefit powerful local industries, such as logging in the West, or oil and gas in Texas.
In the vast majority of cases, a single truck can safely pass over a sound bridge, even if the rig is way over the posted weight limit.
But the cumulative effect of stress on the steel and concrete can eventually prove deadly.
Engineers liken the effect of heavy trucks on a bridge to bending a paper clip: It can bend again and again without breaking, but eventually it will snap.
Many states charge fees ranging from $12 to $1,000 for overweight-load permits, depending on the weight of the load.
In theory, those fees are supposed to offset the damage done to the highways.
Texas, for example, granted nearly 39,000 such permits in the past year, generating $7.5 million, most of which was divided among the state’s 254 counties for road maintenance.
“That in no way even comes close to covering the wear and tear on our roads and bridges in this state,” said Chris Lippincott, a spokesman for the Texas Department of Transportation.
Darrin Roth, director of highway operations at the American Trucking Association, said it is not fair to put all the blame on trucks because permit loads are a tiny proportion of total traffic.
States allowed more than 500,000 overweight trucks to traverse the nation’s bridges and highways at will in the past year, according to an AP review of figures in all 50 states. Those permits were good for an entire year. While 10 states do not issue yearlong permits, all states hand out shorter-term permits good for a few days, weeks or months. Those add up to more than 1.8 million permits not included in the AP’s count.
Many states, including Texas, have reported a modest increase in the number of overweight-load permits issued in recent years – a rise that Roth said can be attributed to a 2.5 percent to 3 percent annual increase in truck traffic because of the growing economy.
California is more cautious with its overweight permits. Truckers in California, where about 23,000 single-trip permits are issued annually, must request permission to travel on a specified route for each trip.
California transportation officials said they perform an extensive review to ensure the load can safely travel on the requested highways without damaging pavement and bridges. Often, truckers are required to reduce their loads.
But in Colorado, where almost 21,000 permits are issued annually, truckers are given a map with their overweight permits showing how much weight bridges around the state can handle. Drivers there operate on the honor system, and officials say they have no way of knowing if drivers are taking bridges appropriate for their loads.
“There’s definitely room for improvement,” said Colorado Transportation Department spokeswoman Stacey Stegman. “But by no means are we alarmed.”
The danger is magnified by a recent federal finding that 18 percent of the nation’s bridges either do not have weight limits posted or incorrectly calculated the weight limits that are posted. Also, a federal study last year classified 26 percent of the nation’s bridges as either structurally deficient or functionally obsolete.
In the year before the Minneapolis disaster, the cause of which is still under investigation, the state Transportation Department granted permits for 48 overweight loads, including construction cranes and supplies weighing as much as 72½ tons.
The bridge had been categorized as structurally deficient, one of over 73,000 U.S. bridges with that designation last year.
Generally, trucks are not allowed to exceed the 40-ton weight limit on interstate highways. However, some stretches of interstate have higher weight limits because they were grandfathered in when the federal interstate system was created during the Eisenhower administration.