After discovering that a few of his co-workers biked to work in the winter, Luke Van Santen was “overwhelmed” by the idea of pedaling through slush and snow. Then he started asking questions: Do you need superwarm clothing? Don’t you have to worry about salt chewing up your bike? Is it safe?

This winter — his second commuting by bicycle — the 45-year-old is now the one fielding questions.

“It’s kind of a low-level curiosity,” he said. “ ‘Oh, you ride your bike in the winter. Oh, you’re kind of crazy, right?’ ”

That kind of crazy is increasingly common. The number of people biking around Minneapolis and St. Paul rose 13 percent this year and 78 percent since 2007, according to a new count by Bike Walk Twin Cities, an advocacy group. Far fewer people ride during the winter, but over the past five years, cold-weather riding has increased at an even greater rate than in summer.

“More bicyclists are choosing to extend their season,” said Joan Pasiuk, director of Bike Walk Twin Cities, a program of the nonprofit Transit for Livable Communities. “People are understanding that winter bicycling can be safe, convenient, faster sometimes, and fun.”

The organization’s annual count, conducted in September with the help of volunteers at 43 spots across the Twin Cities, jibes with the latest census data. About 11 percent of Minneapolis residents reported biking or walking to work in 2012 — an increase of 25 percent from 2011, according to the American Community Survey released in September. Minneapolis is No. 2 in the nation in bike commuting, per capita, after Portland, Ore., the survey found.

A cyclist took a bridge over Hiawatha Avenue in Minneapolis. “More bicyclists are choosing to extend their season,” said the director of Bike Walk Twin Cities.

The swell of people pedaling, even in the cold, reflects a dramatic expansion of bike trails and lanes that make biking safer and more accessible, the Bike Walk Twin Cities report argues. Counts done at locations with new facilities, including bike lanes, showed bigger bumps in bicycling traffic than those without.

An analysis of the Martin Olav Sabo Bridge and 28th Street crossing at Hiawatha Avenue indicates that rather than simply rerouting bikers, “the new bridge has helped encourage new users,” the report says.

Will Mackin, service coordinator at the Hub Bike Co-op, rides to work on Riverside Avenue, which was repaved as part of a reconstruction that added a bike lane.

“Almost immediately, we saw a big increase in ridership,” he said, plus a bump in business at the co-op’s nearby store, one of three in Minneapolis. Years of rising ridership have driven a slight increase in sales at the co-op, despite a difficult recession, he said.

Winter riding equipment — including tires with metal studs and bright LED lights — has gotten cheaper in recent years, Mackin said, making it “more accessible to more people.”

Abbey Seitz, a senior at the University of Minnesota, took a city-planning course in Honolulu, where she expected that there would be “people biking everywhere.”

“Obviously, it’s the perfect climate,” said Seitz, who is studying architecture. “But the roads and everything were not safe at all.”

Honolulu has worked in recent years to improve its biking infrastructure, Seitz said, but it’s playing catch-up with other cities. It has about half the share of bike commuters as Minneapolis and ranks 12th in the census survey.

Studying in Honolulu dissuaded Seitz of the notion that biking participation was related to climate. “It was eye-opening,” she said. Here, people bike in winter because “the city is built for it.”

Van Santen, who uses the Cedar Lake Regional Trail and Midtown Greenway, likes “that added feeling of safety” that trails separated from traffic provide, especially in winter.

He also appreciates their quiet calm as it starts to snow. “It feels very much like a walk in the woods that everybody waxes poetic about.”

The walking half of the Bike Walk Twin Cities’ new count showed a 6 percent decline in pedestrian traffic from 2012 to 2013. But such traffic has increased 16 percent since 2007, when the count began.

The report zeroed in on bridges, where all kinds of traffic converge. At six bridges, walkers and bikers made up 16 percent of traffic.

The report does not say whether that percentage has changed over time. That might be something the program studies in the future, she said, along with the gender of cyclists not just during the September count, but during winter months as well.

Funding for Bike Walk Twin Cities was done on a pilot basis. The program will wrap up some of its projects in 2014 and continue its monthly counts as it looks for new funding, Pasiuk said. Data around cars is “voluminous,” she said, while tracking bikers and walkers is “an emerging science.”

“It’s important as we’re making resource decisions to be able to demonstrate that there are road users who are not behind the wheel.”