Seattle-area traffic congestion was the 19th-worst in the nation in 2005, according to the latest Urban Mobility Report released Tuesday...

Seattle-area traffic congestion was the 19th-worst in the nation in 2005, according to the latest Urban Mobility Report released Tuesday by the Texas Transportation Institute.

The report, which analyzes traffic data in major metropolitan areas around the country, says Seattle-area commuters spent an average of 45 hours in slowdowns on highways and major arterials that year.

Los Angeles had the most congestion, with an average 72 hours of delay, followed by Atlanta, San Francisco-Oakland and Washington, D.C.

Seattle’s rating has improved since 1999 when its congestion ranked second-worst in the nation. Transit use and ridesharing are relatively high here, and recent studies take that into account.

This year’s report says Seattle commute times are not deteriorating as quickly as they are in some areas.

Nonetheless, to guarantee arriving on time for an “important trip,” Seattle-area travelers have to multiply the trip time for free-flowing traffic by 2.06. So if a trip requires 20 minutes going the speed limit, travelers need to allow 41 minutes to account for stalled vehicles, bad weather or construction delays.

The transportation institute is a branch of Texas A&M University. Its report is the nation’s most closely watched ongoing study of congestion trends.