The U.S. trucking industry is an increasingly large part of our transportation system. Trucks deliver nearly 70 percent of all domestic freight. And as our economy strengthens and consumer demand increases, policymakers must update existing laws to ensure the safest, most efficient, and most cost effective fleet on the roads.

We have all seen twin or “pup” trailers on the road. Typically pulled in tandem, their 28-foot length was set by Department of Transportation regulations in 1982 – long before state of the art safety and emissions reduction equipment was developed and deployed. Unfortunately, this 30-year-old rule typically results in trailers filling up before the weight limit is met. In trucker jargon, they “cube out” before they “weigh out.”

Members of Congress may soon consider an important proposal to allow a five-foot extension to 28-foot less-than-truckload (LTL) twin trailers, also known as “twin 28s.” This small yet significant change would bring about dramatic improvements, including cost savings, increased highway safety, and benefits to the environment. 

This modest increase would eliminate approximately 6.6 million truck trips per year, reduce carbon emissions by 4.4 billion pounds, save 204 million gallons of fuel, and eliminate 912 highway accidents annually, all without any change in the federal weight standard. In short, we estimate sanctioning 33-foot pup trailers would have the same overall effect as taking 1.5 million passenger cars off the road.

We have hundreds of miles of HOV lanes which are designed to encourage more efficient utilization of our passenger cars – but we actually have laws which limit the efficiency with which we deploy our fleet of trucks.

Consider how we approach passenger vehicles.  We have hundreds of miles of HOV lanes which are designed to encourage more efficient utilization of our passenger cars – but we actually have laws which limit the efficiency with which we deploy our fleet of trucks.

The Transportation Research Board (TRB) of the National Academies recognized this issue more than a decade ago when calling for a five-foot extension for twin 28s. The logic was and still is simple: freight transportation is more productive if a single truck can haul more cargo.

Poor utilization in truck capacity results in substantial fuel waste and increased levels of greenhouse gas emissions pumped into our atmosphere. It also increases congestion on our highways. According to the Federal Highway Administration miles traveled by vehicles on U.S. roads reached an historic high—1.5 trillion miles in the first half of 2015.  By reducing the number of trucks on the road, we can help alleviate congestion and improve overall fuel economy.

One group focused on improving freight transportation, the Coalition for Efficient & Responsible Trucking (CERT), also found a five-foot length increase could result in 18 percent more goods transported while reducing truck traffic by 1.3 billion miles per year.

Longer pup trailers would not pose safety risks in stopping distance because the weight limit would remain the same. One study by commercial transportation expert John Woodrooffe at the University of Michigan asserts that twin 33s are “inherently more stable” and subsequently safer than twin 28s due to the longer wheelbase.

A handful of states already allow 33-foot twins and have remarkable track records. On the nation’s third-busiest toll road, the Florida Turnpike, twin 33s have traveled more than one million miles over the past five years without a single accident.

There is no silver bullet for addressing shipping efficiency, climate change, and highway safety; however, twin 33-foot trailers move the needle closer and deserve support in Congress. 

Carl Pope is the former Executive Director of the Sierra Club

Mark Rosenker is the former chairman of the National Transportation Safety Board (NTSB) and current senior adviser to the Coalition for Efficient and Responsible Trucking.