TTI report ranks congested, unreliable traffic corridors

Bill Eisele Bill Eisele Tim Lomax Tim Lomax

A new report by the Texas Transportation Institute ranks 328 seriously congested highway corridors across the U.S. for the first time by morning and evening drive times, middays and weekends.

“Until now, we’ve been able to measure average congestion levels,” said Bill Eisele, TTI research engineer and visiting associate professor of urban planning at Texas A&M’s College of Architecture, “but congestion isn’t an ‘average’ problem.”

The rankings also include “reliably unreliable” corridors with the most day-to-day variations in congestion. Not only were they found to have more stop-and-go traffic than others, they were also much less predictable, meaning commuters and truckers have a difficult time knowing how much time a trip using these corridors roads will take, despite taking the same route.

The rankings include highway corridors generally parsed in 3-8 mile ranges: for example, Austin’s 6.7 mile stretch of southbound Interstate 35 from U.S. 183 to Woodland Avenue was ranked the 7th most congested corridor in the U.S. in the 3-7 p.m. afternoon drive time.

The number of Texas highway corridors, by city, appearing in TTI’s lists of the 40 most congested in the U.S.:

• Morning drive time, 6-10 a.m., Houston 6, Dallas/Fort Worth 2;
• Afternoon drive time, 3-7 p.m., Houston 6, Dallas/Fort Worth 2, Austin 2;
• Midday hours, 10 a.m. - 3 p.m. Houston 4, Dallas/Fort Worth 1, Austin 1.
• Weekend, covering all day Saturday and Sunday, Austin, 2, Houston 1.
• Truck congestion, covering all days of the week, showed Austin with 2 corridors and Houston 1.

In the “reliably unreliable” category were Houston 2, and Dallas/Fort Worth 1.

San Antonio did not have any roads in the top 40 in these categories.

Among the report’s findings:
• The 328 most congested corridors in the U.S., while accounting for only six percent of the nation’s total freeway lane miles and 10 percent of the traffic, account for 36 percent of the country’s urban freeway congestion;
• The 328 corridors account for eight percent of the national truck traffic and 33 percent of urban freeway truck delay;
• Travel time reliability is more of a problem around bridges, tunnels and toll facilities because there are few alternate routes available in such circumstances and because a small incident can have a huge effect on corridor travel times.

As the first national look at travel time reliability, TTI researchers believe the report can be useful in determining where transportation system improvements will have the greatest impact, and that there is no single best way to fix the problem.

“If cities and states make the right investments in our most congested highway corridors, the return on those investments will be substantial,” says study author Tim Lomax, a research engineer at TTI and urban planning lecturer at the College of Architecture. “Not only will we see more reliable trips for travelers and trucks, but we can also expect to see greater productivity and more jobs.”

TTI is an agency of the Texas A&M University System.

posted November 22, 2011