Seattle-Tacoma Traffic Among Most Unpredictable in US—How Long is Your Commute?

Heavy traffic is nothing new in the Puget Sound area, but a new study shows the severity of our rush-hour jams is especially tough to predict.

The latest Urban Mobility Report, released today by the Texas A&M Transportation Institute, shows drivers in the Seattle metro area, which includes King, Pierce and Snohomish counties, spent an average of 48 hours—two whole days—sitting in traffic in 2011.

That figure ties Seattle-Tacoma with Philadelphia for ninth-place among the country's 15 largest metro areas when it comes to average hours lost to traffic congestion.

The study focuses on freeway drive times and in Kirkland, of course, Interstate 405 through town is considered the worst. Washington State Department of Transportation statistics shows rush hour "throughput" actually improved 4 percent on I-405 northbound at 160th in Kirkland from 2009 to 2011, but declined 3 percent in the southbound lanes during that period.

Another aspect of the Texas A&M Transportation Institute study shows our region's traffic isn't just heavy—it's also highly unpredictable.

For the first time, researchers also measured the amount of a time a driver must plan to ensure on-time arrival 19 out of 20 times. Seattle-Tacoma's "Freeway Planning Time Index" came in at 3.99, meaning commuters must set aside 80 minutes to consistently arrive on time when traveling on a route that takes 20 minutes in light or no traffic.

The figure puts traffic the Puget Sound region at 12th most-unreliable out of 101 urban areas across the country. Despite a significantly smaller population, nearby Portland actually scored higher than our area, with an index of 4.26.

Congestion in our region got slightly worse in 2011, according to the study, with the average number of hours lost in traffic increasing from 47 to 48. But these figures are markedly lower than 2006, when the average was 54 hours.

How much time do you set aside for your daily commute? Tell us in the comments section.