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Study Shows How Traffic Patterns Change

Logjams in Americans' daily commutes are affected by actions both great and seemingly insignificant, says a new report by a company that tracks traffic congestion in the USA.

Long-term congestion can be caused by something as huge as a catastrophic bridge collapse, as occurred in Minneapolis in 2007, according to INRIX's 2009 National Traffic Scorecard.

Congestion can be eased by something as simple as engineers re-striping an interstate ramp to create two lanes out of one, which happened last year in the San Francisco Bay Area.

On Aug. 1, 2007, a 1,000-foot-long bridge on Interstate 35W in Minneapolis collapsed, killing 13 people and injuring 145. The collapse caused backups on surrounding roads as motorists sought alternate routes.

The state converted a 4-mile stretch of State Route 280, which runs parallel with I-35W, to a limited-access freeway to ease north-south traffic and repaved and re-striped I-94 to add one lane in each direction for east-west traffic, Minnesota Department of Transportation spokesman Todd Kramascz says.

Minneapolis, which had been the nation's 13th-most-congested city in INRIX's 2007 annual ranking, moved into the Top 10 at 10th in 2008. A $234 million bridge opened in September 2008, and Minneapolis dropped to 12th last year.

In Marin County, Calif., a bottleneck created by westbound traffic on Interstate 580 merging onto northbound U.S. 101 was the nation's third-worst in INRIX's 2007 rankings and fourth-worst in 2008. In 2009, officials re-striped that interchange to add a second lane, says Lauren Wonder of the California Department of Transportation. Last year, the bottleneck fell to 491st in INRIX's rankings.

Both examples show how changes at one point in a metropolitan region's transportation network can ripple across the entire system, says Rick Schuman, author of INRIX's annual National Traffic Scorecard.

According to INRIX, the worst bottleneck in the nation is New York's Cross Bronx Expressway westbound approaching the Bronx River Parkway. "You could walk the Cross Bronx faster at certain times of day than you can drive it," Schuman says. "The good news is its average speed has moved up from 9.8 mph in 2007 to 11.4 mph now."

Drivers in the Bay Area might soon find themselves once again near the top of the worst bottlenecks list. Wonder says that in April, the interchange of westbound I-580 to northbound U.S. 101 will be re-striped back to one lane - but only temporarily.

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