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Large trucks on America's interstates could become 20 percent heavier. The Coalition for Transportation Productivity, a group of more than 100 major shippers including Coca-Cola and The Home Depot, is supporting legislation in Congress that, proponents say, would increase efficiency and reduce emissions.

"With the Panama Canal being deepened, these larger cargo ships coming in are going to be carrying containers that weigh 97,000 pounds," said Rep. Lynn Westmoreland (R-GA). "If we continue to have our weight limit at 80,000 pounds, then we would have to take the containers, unload them, repack them, put them on trucks and use more trucks to do that."

In 2009, nearly 300,000 trucks were involved in crashes in the United States, according to figures compiled by the U.S. Department of Transportation. Safety advocates argue heavier trucks may cause more serious accidents. But proponents of the legislation say increasing the weight limit would actually reduce the number of trucks on roads, making them safer.

Either way, many state transportation officials worry about the impacts of heavier loads on their roads and their budgets.

"If we advocate for higher weights, it's going to be more wear and tear on our roads, which means more money," said Jim Cole, a board member of the Georgia Department of Transportation. "We have to balance that with an economic picture of the future, as well."

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While GDOT officials have yet to make a recommendation to state legislators, their counterparts in Mississippi are voicing opposition to increased truck weights. Meanwhile, Maine and Vermont have already been testing special six axle trucks weighing up to 100,000 pounds.

But large company fleets and independent operators often differ on the short-term impact of the retrofits and upgrades involved with increased loads.

"The manufacturer will be able to offset the equipment with the economies of scale they get, the productivity they get out of it," said Ed Crowell, president of the Georgia Motor Trucking Association. "The for-hire trucker who doesn't do any manufacturing will be faced with the cost, but all the benefit will go to the customer."

The proposed legislation would allow individual states to opt out, leaving an open question as to whether the U.S. continues its patchwork of weight limits, or whether the heavier trucks become the new normal.