New census data confirms what's immediately clear to any casual observer in Portland: bicycling has caught on in the city in a big way.

About one in 23 workers in Portland commute to work by bike. That's about 4.4 percent of Portland workers 16 and older. This is up from 3.7 percent in 2005 and 3 percent in 2004, according to the U.S. Census Bureaus American Community Survey.

Biking was still much less popular than other ways of getting to work: 5.5 percent of people usually walked to work last year, 11 percent carpooled, 13.5 percent took public transport and 64.5 percent of workers drove alone.

But the share of drivers is shrinking, down 5.2 percent from 1996 to 2006 for solo drivers and 12.5 percent for carpoolers.

City estimates also show an upswing in biking. On the average late-summer day, city data shows 14,563 people biked across the four Willamette River brides that carry the most bike traffic. That was a nearly 21 percent leap 2006.

Transportation advocates say there are a multitude of reasons for the growth in bike commuting, including rising gas prices, health concerns and a city that's added bike lanes and increased bike parking.