Reliably Unreliable

The Congestion Problem: TTI identifies the worst stretches of highway that offer unpredictable travel times.

In the first nationwide effort to identify specific stretches of highway responsible for significant traffic congestion at different times and on different days, the Texas Transportation Institute’s (TTI) 2011 Congested Corridors Report helps motorists ascertain exactly where to expect traffic delays and how to plan for them.

The 328 corridors studied in the Texas Transportation Institute’s 2011 Congested Corridors Report represent just 6 per­cent of the nation’s lane miles, but account for 36 percent of the country’s urban congestion.

Researchers for the TTI (a Texas A&M University System agency) report noted that the corridors included in the report were identified by the data itself.

INRIX, a traffic data and analytics provider, originated the corridor approach using 10 hours of congestion per week to define a starting point for a congested corridor. To be considered a “corridor,” according to the INRIX standard adopted for this report, congestion should impact a freeway segment at least 3 miles long.

“Until now, we’ve been able to measure average congestion levels, but congestion isn’t an ‘average’ problem,” TTI Research Engineer Bill Eisele noted in a written statement about the report.

The report describes congestion problems in 328 seriously congested corridors over a variety of times — all day, morning and evening peaks, midday, and weekends. Not only were these roads found to have more stop-and-go traffic than others, they were also much less predictable — “so, not only does it take longer, commuters and truckers have a difficult time knowing how much longer it will take each time they make the same trip,” said co-author David Schrank.

However, even more significant, Eisele told Aggregates Manager, is that the 328 corridors studied represent just 6 percent of the nation’s lane miles, but account for 36 percent of the country’s urban congestion.

“There are a relatively small amount of roads representing more than one-third of the congestion on roadways,” Eisele said in a phone interview. “This is striking. These are the places that are ripe for investment.”

How investment is made will vary depending on location. In some areas, Eisele pointed out, investment might mean additional lanes or additional transit such as rail or bus. In other areas, it might mean aggressively clearing crashes off of a highway so additional congestion is not endured.

“It comes down to reassessing how and when we use the roadway system,” Eisele said. “Do we all need to drive at the same time? Flex time and telecommuting could make some impact on congestion.”

Although there is no single best way to fix the problem, the best solutions will come from efforts that have meaningful involvement from everyone concerned — agencies, businesses, and travelers.