Bicycle traffic in Portland grew by more than 6 percent in 2011, with more bike commuters riding on the city's low-traffic neighborhood greenways, according to

data released late Friday.

According to the study, an average of 18,257 bicyclists per day crossed the Willamette River via the four bike-friendly bridges -- the Hawthorne, Steel, Burnside and Broadway. That’s an increase of 4 percent over 2010.

Bridge bike traffic increased despite an 18 percent decline in counted bicyclists on the Broadway Bridge, which city officials blamed on construction of a Portland Streetcar extension across the river.

The streetcar project required detours and sidewalk closures through last summer on and around the Broadway. “Some cyclists were avoiding that area,” said traffic engineer Rob Burchfield. “It was not necessarily a pleasant place to ride.”

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Citywide, PBOT bike counts, conducted at more than 156 locations around Portland by trained volunteers and automatic hoses on bike routes, showed a 6.4 percent jump in bicycle trips overall.

It was the second straight year of growth in bike commuting,

. In 2009, the city registered its first decline in bike traffic in years, which was largely attributed to the recession.

Burchfield and other PBOT officials said a combination of higher gas prices, population growth and an improving job market were likely behind the growing number of bike commuters in 2011.

The 2011 “bike counts” study also recorded 61 percent more bicyclists at 11 locations on low-traffic and low-speed neighborhood greenways paralleling busy streets.

Despite a big push to build bicycle lanes and bikeways,the vast majority of the Portland region’s residents still prefer to drive alone to work daily,

.

But last fall, an analysis by

showed Portland led the nation with a bicycle-commuting rate of 6 percent.

Long known as “Bike City U.S.A.,” Portland was once the clear winner in the contest for America's most bike-friendly large city.

But in recent years, Minneapolis has caught up to and even passed the Rose City,

, with Chicago, Boulder, Colo., and New Orleans picking up speed.

In fact, Chicago Mayor Rahm Emanuel has set a goal for his town to become the bike-friendliest city in America.

Other key findings of Portland's 2011 “bike counts” study:

East Portland and Northeast Portland led the growth in bicycle trips with 18 percent and 16 percent increases, respectively.

80 percent of counted bicyclists were wearing helmets, a 3 percent increase over 2010. Women were more likely to wear helmets while biking, according to the study.

69 percent of bicyclists were male, while 31 percent were female – the same as 2010.

7 percent more bicycles were counted at non-bridge locations citywide.