State transportation leaders want to ease restrictions on the weight trucks carry on Minnesota roads, despite concerns that heavier loads may shorten the lifespan of bridges.

Trucks moving certain farm and timber products already have permission to carry extra loads, thanks to recent state laws passed at the request of those industries.

Advocates for a broader change to the state's weight restriction argue that the step would make hauling more efficient and help them compete with the Dakotas and Canada, which allow heavier trucks.

Opponents contend big trucks are a safety hazard and will wear out bridges faster. And in the aftermath of the Interstate 35W bridge collapse, some lawmakers say potential damage to bridges -- and who pays for it -- must be a part of the discussion.

But the need for more efficient shipping methods is growing.

The North American Free Trade Agreement has dramatically increased international trade. "Just-in-time delivery" methods demanded by big-box retailers have turned highways into rolling warehouses. And now, Midwestern states such as Minnesota are seeking better ways to move corn to ethanol distilleries.

Gov. Tim Pawlenty's administration met resistance when it proposed a general elevation of truck weight restrictions in 2006. So in this year's session, MnDOT put the proposal on hold and lent its support to industries pushing their own legislation as long as they followed agency recommendations, said Betsy Parker, MnDOT's government affairs director. They include adding axles to spread the weight over more tires, and posting restrictions or closures on bridges that can't bear heavier loads.

MnDOT still backs higher weight restrictions because of a 2006 study that concluded they would make deliveries more cost-efficient and may even do less damage to pavement, according to Cecil Selness, the agency's director of freight and commercial vehicle operations. "The other part that we looked at is, if you can carry more per truck you can reduce overall the amount of trucks that are in the traffic mix, and that has a positive effect," Selness said.

U.S. Rep. Jim Oberstar, a Minnesota Democrat and chairman of the House Transportation and Infrastructure Committee, said in a recent interview that MnDOT's cost-benefit claims are unproven. He said he has been fighting proposals to allow heavier trucks on interstates for many years because of safety concerns and because the shipping industry has not been willing to pay for the damage it would do.

"And one of the consequences of increased weight is the effect on bridges and road surfaces," Oberstar said. "If they deteriorate faster, then someone has to pay for that."

The nonpartisan Congressional Research Service said in a 2005 report that growing reliance on trucks to move grain has led to increasing concerns with wear and tear on rural roads and bridges.

A MnDOT study recommends allowing heavier trucks on state and some county roads even though it would cost about $2.7 million a year in additional bridge costs. MnDOT's Selness said he assumes the expense would be paid like any other highway project; the study didn't address funding.

Steven Frank, president and CEO of the American Automobile Association of Minneapolis, said it wasn't much of a study at all; he called it an "advocacy project."The foregone conclusion was that truck weights would be increased, and it was just a matter of determining the best way to get it done," Frank said.

Study recommendations

The "Minnesota Truck Size and Weight Project" study, conducted for MnDOT by Cambridge Systematics Inc. of Bethesda, Md., offered a number of recommendations, including an expansion of the state's system of heavy-duty roadways and more "flexibility" for weight limits and vehicle configurations.

The report recommends increasing truck weights from the current 80,000 pound cap to between 90,000 and 108,000 pounds, depending on the number of axles and how they are configured.

Nearly everyone seems to agree that regardless of their effect on pavement, heavier trucks wear out bridges faster.

A 2003 study by the University of Minnesota concluded, "Any increase in legal truck weight would shorten the time for repair or replacement of many bridges."