A study requested by Congress recommends that the federal government consider allowing heavier trucks and longer combination vehicles on Interstate highways.

The report by the National Academies' Transportation Research Board was requested by Congress as part of 1998 highway funding legislation. The findings of this study will no doubt be part of the reauthorization debate next year.
With bigger vehicles, the research notes, freight can be moved at lower costs. But given federal size limits, larger trucks sometimes bypass interstate highways -- the safest and most efficient roads -- to use secondary roads where accidents are more likely to happen and maintenance costs are higher.
States should be allowed to issue permits for the operation of six-axle tractor-trailers weighing up to 90,000 pounds, the report says. The current federal limit is 80,000 pounds, and the standard tractor-trailer has five axles. Compared to the five-axle truck, the six-axle truck reduces shipping costs moderately, and its lower weight-per-axle ratio cuts down on pavement wear. However, increasing the total weight of trucks increases bridge construction and maintenance costs.
The report also recommended that double trailers as long as 33 feet each should be permitted, making the trailers 5 feet longer than the 28-foot double trailers that are most common today, the report says.
These double trailers and the 90,000-pound tractor-trailers should only be operated in states that choose to allow them, and only by carriers who receive special permits from the states, added the committee. Participating states would be required to meet federal standards regarding enforcement, fees paid by permit recipients, safety requirements, and management of effects on bridges.
The committee that wrote the report said Congress should charter a new federal organization to oversee implementation of federal regulations and evaluate their results, carry out pilot studies and research to determine the impact of trucks on highways, and recommend new regulations based on its findings.
“We discovered a lack of information about the costs and benefits of larger trucks and the impact of regulations,” said the committee chairman. “To determine and enact limits that are based on facts, this nation needs a program that observes and evaluates the consequences of truck traffic.”
Darrin Roth, director of highway operations for the American Trucking Associations, told the Associated Press that “there really is no correlation between increased weight and reduced safety. Given the record and given the research, the opposite is true. You can increase weight and have a safety benefit.”