A coalition of highway-safety advocates asked the Senate today not to consider language in a bill funding the Department of Transportation for the 2016 fiscal year that would expand the length of twin tractor-trailers operating on the nation's interstate highway system.

The plea comes several days after the House Appropriations Committee passed a bill that included such language in its funding for DOT, the Department of Housing and Urban Development, and related agencies in the 2016 fiscal year. The House bill would expand the length of each trailer to 33 feet; the length of twin trailers operating on interstate highways is capped at 28 feet, though 18 states allow 33-foot trailers in a double hook-up on their parts of the interstate system. The 28-foot limit has been in effect since 1982.

In the letter, the "Truck Safety Coalition," a group composed of "Citizens for Reliable and Safe Highways" and "Parents Against Tired Truckers," said a truck carrying two 33-foot trailers would be 84 feet long, equal to the height of an eight-story office building. By making 33-foot twin trailers the law of the land, Congress will create a climate that will result in "more in terms of highway congestion and crash-related cleanup costs after an accident has taken place," the group said in the letter, which was not addressed to a specific Senator.

Several days ago, 10 groups, including the U.S. Chamber of Commerce, the National Retail Federation, the National Industrial Transportation league, and Volvo Group North America wrote to Rep. Hal Rogers (R-Ky.), chairman of the House Appropriations Committee, asking him to support the initiative. The groups said that because the 33-foot configurations have a longer wheelbase, the tractor-trailers will handle better than the 28-footers in straight-line driving and cornering. Tests in Canada and in select U.S. markets support the claim that the larger trailers are more stable than the smaller versions, the groups said.

Allowing larger trailers on the road would reduce truck trips because shippers could put more goods in each trailer, the groups said. This would result in 6.6 million fewer truck trips a year, a 1.3-billion-mile reduction in truck traffic, a 4.4-billion-pound cut in carbon emissions, and 912 fewer crashes, according to the groups.

Shipper, trucker, and other business interests have long advocated for what they consider to be a modest increase in trailer lengths. Most twin trailers are used by parcel and less-than-truckload (LTL) carriers, whose cargo routinely fills all the available trailer space long before the 80,000-pound gross vehicle weight limit—the combined weight of tractor, trailer, and cargo—is reached. The increase in trailer length would enable carriers and shippers to more efficiently utilize a trailer's cubic capacity, according to business interests.

Supporters of the change said it would add 16 percent more cubic capacity without adding miles traveled or increasing a vehicle's weight beyond the legal limit. Because the explosive growth in e-commerce will increase demand for the delivery of lighter-weight, bulky packages that cube out before they weigh out, the 10-foot total cubic-foot increase will lead to a dramatic improvement to truck productivity without compromising safety, they said.