ON A RECENT SUNDAY, Brandon Jones, a 44-year-old fund manager at 9W Capital Management, traveled from his home in downtown Manhattan with his wife and two children to meet friends for brunch in Williamsburg, Brooklyn. They were heading to Reynard, the popular restaurant in the neighborhood's fashionable Wythe Hotel, where Manhattan-bound Town Cars regularly idle on the street outside.

But Mr. Jones did not drive. Nor did he take the subway. Instead, he piloted his two children via the deck of his Yuba Mundo, a so-called "longtail" cargo bike. (His wife rode her own bike.) Picture a mountain bike, but with a stouter frame and smaller wheels, stretched out and lowered in the back. "We actually beat our friends who drove back to TriBeCa," Mr. Jones said. While Mr. Jones does garage a BMW X5 SUV, his car rarely sees daylight within the city limits. Rather, for daily trips like the mile-and-a-half commute from TriBeCa to his children's school in Greenwich Village, he simply hops on another kind of SUV—one that actually includes a bit of sport.

Mr. Jones's choice is becoming an increasingly popular one in the U.S. The country's biggest seller of the Yuba Mundo is Joe Bike, a Portland, Ore., store specializing in "high-performance urban, utility and touring bikes." The owner, Joe Doebele, said that when he began carrying cargo bikes—a catchall term covering a variety of bike styles built for functional hauling—five years ago, he thought they would be for just that, cargo. "But parents, mostly moms, were the ones who were buying them," he said. "It quickly became a family bike."

Mr. Doebele attributes the interest to Portland's "mini baby boom" and the fact that many young families are choosing to stay in cities like Portland instead of moving to the suburbs—not to mention higher gas prices.

Then there's the expansion of cycling's popularity in the U.S., with most cities reporting double- or even triple-digit gains from 2005 to 2011, according to the League of American Bicyclists. New York and Chicago have launched new bike-share programs. Indianapolis and Atlanta have ambitious walking-and-biking networks, the former an 8-mile "Cultural Trail" (with a planned bike-share program to boot), the latter a 33-mile "BeltLine." And according to People for Bikes, a Boulder, Colo.-based national advocacy group, the number of bike lanes built nationwide through its Green Lane project is expected to double this year to over 200 across multiple cities.