A former chairman of the National Transportation Safety Board (NTSB) has called on members of the Senate Appropriations Committee to approve language in the upcoming fiscal year 2016 appropriations bill for the departments of Transportation and Housing and Urban Development that would expand the length of twin trailers operated by less-than-truckload (LTL) carriers on the nation's interstate highway system.

Mark V. Rosenker, who chaired the NTSB from August 2006 to August 2008 and served on the Board for seven years, said a "modest extension" of twin trailers to 33 feet each from the current 28-foot configuration would have no bearing on the current federal truck gross vehicle weight (tractor, trailer, and cargo) limit of 80,000 pounds, would require no public investment, and would increase a tractor-trailer's productivity by up to 18 percent by enabling more efficient cubing of trailer space.

Rosenker is president of consultancy Transportation Safety Group LLC and senior advisor to the Coalition For Efficient and Responsible Trucking (CERT) a group that supports the proposal.

In a letter written to Sens. Thad Cochran (R-Miss.), chairman of the Senate Appropriations Committee, and Barbara Mikulski (D-Md.), the committee's ranking member, Rosenker called the proposed change "sound public policy" that will result in "less wear and tear on our infrastructure, fewer trucks on the road to move the same amount of freight, and reductions in greenhouse-gas emissions."

Earlier this month, the House passed a $55.3 billion fiscal-year 2016 appropriations bill for the departments of transportation and housing and urban development that includes language allowing twin 33-foot trailers to operate nationwide on the interstate system.

Currently, federal law places a 28-foot limit on the length of each trailer hooked in tandem behind a tractor running on the interstate system. Eighteen states currently allow 33-foot twin trailers to run on their parts of the interstate. Opponents such as the Teamsters Union argue the highway system's merge lanes and on-off ramps are not designed to accommodate tractor-trailers that, with the longer trailers, would measure 84 feet in length.

Supporters, notably Frederick W. Smith, chairman and CEO of Memphis-based FedEx Corp., maintain the longer trucks will increase truck productivity by optimizing each trailer's cubic capacity. They also contend that trucks carrying 33-foot trailers with longer wheelbases will handle with more stability than rigs hauling 28-foot trailers.

The longer trailers would benefit LTL and parcel carriers that deliver large amounts of lighter-weighted and high-cube goods that fill up a trailer's capacity long before the cargo approaches the 80,000-pound gross vehicle weight limit.

Backers of the proposal contend that the growth of digital commerce over the next 10 years will result in a 40-percent increase in LTL shipments that will move in 28-foot twin trailers. About 1.2 million more trucks will be needed to meet that demand, they argue. Most of the goods ordered online are lightweight shipments that often cube out before they weigh out.

Adding five feet to the length of each trailer would cut 6.6 million truck trips per year, prevent 912 crashes each year, and reduce fuel consumption by 204 million gallons annually, supporters said.