Traffic congestion on the 161,000-mile National Highway System (NHS) in 2015 imposed more than $63.4 billion in additional operating costs on the trucking industry, a 30-percent increase over 2014 totals, according to a report released today by the American Transportation Research Institute (ATRI), the non-profit research arm of the American Trucking Associations.

According to the report, the delays on the national system—the world's largest—resulted in more than 996 million hours of lost productivity during 2015. This was equal to more than 362,000 commercial drivers sitting idle for an entire year, ATRI said.

"This is more than a cost to the trucking industry. This is a cost to the U.S. economy," ATRI President Rebecca Brewster told reporters today in a conference call.

In 2014, congestion imposed an additional $49.6 billion in costs on the industry, resulting in 728 million hours of lost productivity and equaling 264,500 drivers sitting idle for a year. There were 11.2 million registered trucks in 2015, compared with 10.9 million in 2014. Vehicle miles travelled in 2015 increased to 279.8 billion vehicle miles from 279.1 billion in 2014, according to ATRI data.

In an e-mail, Brewster said a key factor in the year-on-year increases was the Federal Highway Administration's (FHWA) conversion in 2015 to a more comprehensive dataset, which provided ATRI with greater insight into congestion trends. Congestion was affected by a dramatic increase in road accidents, a double-digit surge in e-commerce activity that put more delivery trucks on the road, and the impact of a January 2015 blizzard in the northeast, according to ATRI data. According to the analysis, 91 percent of the total 2015 congestion cost occurred in heavily populated urban areas, with 88 percent of the congestion costs concentrated in only 17 percent of the network mileage. The top 10 states each experienced congestion-related costs of more than $2 billion, with Florida and Texas each toting up more than $5 billion in additional cost. Ohio showed the largest percentage year-over-year increase, up 171.3 percent to nearly $2.5 billion.

The typical truck travelling 100,000 miles or more across the country in 2015 bore an added cost of $22,676 due to congestion, according to ATRI data. Across the entire registered truck network, congestion added $5,664 to the operating cost of each vehicle, ATRI said.

The NHS includes the 41,000-mile Interstate Highway System and other roads serving major airports, ports, rail or truck terminals, railway stations, and pipeline terminals, among other transport facilities.