Congestion on the nation’s Interstate highways added over $9.2 billion in operational costs to the trucking industry in 2013, according to research released Wednesday by the American Transportation Research Institute.

The group used motor carrier financial data along with billions of anonymous truck GPS data points to calculate congestion delays and costs on each mile of Interstate roadway. Delays totaled over 141 million hours of lost productivity, which equals more than 51,000 truck drivers sitting idle for a working year.

ATRI’s analysis also established the states, metropolitan areas, and counties with the highest congestion costs. 

California led the nation with over $1.7 billion in costs, followed by Texas with over $1 billion. 

The Los Angeles metropolitan area saw the highest cost at nearly $1.1 billion and New York City was close behind at $984 million. 

Congestion tended to be most severe in urban areas, with 89% of the congestion costs concentrated on only 12% of the Interstate mileage. 

“This concentration of congestion has been well-documented in previous work by ATRI which identified the worst truck bottlenecks in the U.S,” the group said in a release. “Of the 100 worst bottlenecks in ATRI’s 2013 bottleneck analysis, 98 were identified as having “severe” congestion in this cost of congestion analysis.”

ATRI says its analysis also demonstrates the average impact of congestion costs on a per-truck basis.  For example, a truck driven for 12,000 miles in 2013 saw an average congestion cost of $408, while a truck driven for 150,000 miles had an average cost of $5,094.

ATRI is the non-profit research arm of the American Trucking Associations.

A copy of the study results is available from ATRI webiste