Truck and rail traffic are expected to grow, good news for the economy as well as the carriers, but the benefits are not without drawbacks. With growth comes congestion, particularly in cities, and transportation planners need more information and better direction from Congress on how to manage the problem.

That’s the message from the Government Accountability Office, in response to a request by Sen. John Walsh, D-Mont., for an assessment of national freight flows and their impact on congestion.

Under the current highway program, DOT is undertaking a multi-year effort to measure the scope of freight movements as a way to establish priorities and set goals for a National Freight Plan.

As part of that process the department is working out a highway-based Primary Freight Network that will eventually be the basis of the national plan, but the department’s instructions from Congress do not include specific references to freight congestion, GAO said.

“Freight-related traffic congestion affects communities of all sizes in the U.S.,” GAO said.

In some places it has been a problem for decades due in part to inadequate funding. In other areas, such as the Bakken Region of North Dakota where the fracking industry has exploded, it is a new problem.

“Given that freight volumes are expected to increase over the next 25 years and beyond, a growing number of communities will likely be seeking to devise and fund solutions to mitigate the impacts of freight-related traffic congestion.”

Creation of a National Freight Plan provides an opportunity to address the issue, GAO said.

What’s required is a clearer definition of the appropriate federal role, spelling out the goals, objectives and measures for addressing congestion. And planners need more and better data, GAO said.

Another particular that Congress must address is the size of the freight network.

In its initial instructions in the 2012 highway bill, Congress told DOT that the National Freight Network should be limited to 27,000 centerline miles, although that could be expanded to 30,000 miles if necessary.

But in its initial work on the Network, the Federal Highway Administration found that it could not pack all of Congress’s requirements into that number of miles. The agency said the number should be more like 41,500 miles. GAO said Congress needs to either bump up the number, or change other expectations it has for the freight network.

It recommended that DOT take steps to help states define the impact of freight movements on their communities, including standards for data collection and analysis.

And it suggested that the National Freight Strategic Plan include a statement spelling out the federal role in freight-related traffic congestion.

DOT agreed with GAO’s assessment, and said that the Obama administration’s proposed highway bill, the GROW America Act, takes up these issues. It would establish a Multimodal National Freight Network that addresses community issues and collects data through a public process. It also would establish an incentive program that states could use to relieve congestion, and it would require states to develop freight plans that include the impact on communities, DOT said.

Sen. Walsh is a member of the Senate Commerce, Science and Transportation Committee, which is responsible for drafting a portion of the next highway bill.