Interstate 45 in Harris County, Texas, from SL-8 North to I-610, is the most congested roadway segment in the state, according to the Texas Department of Transportation.
A close second is the U.S. Route 59 between I-610 West and State Highway 288.

On the I-45, the annual cost of delay is $98.03 million, and it accounts for 484,630 hours of delay time per mile, per year.

The results are part of the Texas Department of Transportation's updated list of Texas' 100 most congested roadway segments, released Wednesday. In developing the update, the state used actual traffic speed data to calculate delay, rather than estimations based on traffic volume used in the previous list. Parameters for roadway segment length were also adjusted to better capture congested points in the transportation system.

This time around, the list includes the state highway system, and many city, county or toll road segments. It also now considers both weekday and weekend congestion levels to provide a congestion ranking based on delay experienced all days of the week. The Texas Transportation Institute (TTI) at Texas A&M University collaborated with TxDOT to develop the new list and improved methodology.

"Texans have known for some time that traffic is bad - but this new list accurately pinpoints the traffic hotspots in the state, and will help make sure transportation planners consider these roadways when prioritizing roadway and transit projects," said Dr. Tim Lomax, research engineer with TTI, who coordinated with TxDOT staff to develop the list. "TTI has long distributed reports on congestion levels throughout the United States, including those levels in Texas, but the new methods used in this analysis are on the cutting edge of traffic congestion measurement."

To gather actual travel speed data, TTI contracted with Inrix, a private firm that collects real time travel information nationwide and provides that information to a variety of companies for use by the public through GPS units and smart phone applications. Through the contract, TTI received actual speed data for roadways across the state for 2009 to use with traffic volume data to assess total delay.

Previously, the congestion levels were based on traffic volume and used information about operational characteristics to estimate travel speeds. This analysis showed where large volumes of traffic were likely to move at a slow pace, but did not identify where other problems, such as bottlenecks caused by intersecting roadways or poor roadway geometry, are found.

To view the list, click here.