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

ATRI used trucking 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 – equal to more than 51,000 truck drivers sitting idle for an entire working year, ATRI pointed out.

The study also found that among the states, metropolitan areas, and counties with the highest congestion costs, California led 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, ATRI said.

This concentration of congestion was well-documented in previous work by ATRI identifying the worst truck bottlenecks in the U.S. Of the 100 worst bottlenecks found, 98 were identified as having “severe” congestion in this analysis.

The analysis also revealed what were 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 saw an average congestion cost of $5,094.

“Congestion is an unfortunate byproduct of our just-in-time economy, and it’s a significant roadblock to our country’s productivity as well as its global competitiveness,” said Jack Holmes, President of UPS Freight, the heavy freight division of UPS.

“ATRI’s analysis quantifies congestion in a way that clearly shows the urgent need for highway investment.”