“When we first started selling these bikes 15 years ago, we were the total freako weirdos,” said Ross Evans, the company’s founder. “Back then, a basket on your handlebars was considered fringe.”

These days, cargo bikes are no longer a novelty: They are cropping up not just in the expected West Coast enclaves like Seattle, Portland and the Bay Area, but in cities like New Haven, Tucson and Dallas. “It used to be that if I saw somebody in Boston on a cargo bike, I probably knew them and probably helped them buy their bicycle,” said Nathan Vierling-Claassen, who has ridden a cargo bike since 2008. “Now that’s no longer the case.”

Cargo bikes are also popular in Washington. Jon Renaut, 37, a software engineer at the Department of Homeland Security, said that he is one of more than a dozen parents at his children’s elementary school who commute to school and work by cargo bike. “There have been only two days this whole school year — when it was really, really snowy out — that we left the bike at home,” Mr. Renaut said. What helps keep his 4- and 6-year-old daughters warm, he said, is to have them face backward while riding.

The popularity of cargo bikes has given rise to more variety. Cargo bikes come in two main types: longtails, which look like a regular bike with a large rack extended over the rear wheel, and the Dutch-style bakfiets, which has a cargo box mounted in front of the handlebars. While longtails are considerably cheaper (a Yuba Mundo starts at $1,300), bakfiets (which start at about $3,000) can generally hold more.

“The thing I love about cargo bikes these days is that there is such an amazing selection,” said Shane MacRhodes, 43, who manages a school transportation program in Eugene, Ore. “People are finding bikes that really fit their lifestyle. Some people like the sturdiness of a Yuba Mundo, and some people like the sporty zippy ones. It’s almost like the S.U.V. versus the sports wagon.”