Its pedal-powered technology stretches back two centuries, but like the latest, hottest gadget, Divvy has in two years gone from “Will anyone use it?” to “Does anyone not?” It’s not just that unlimited rides are much cheaper on Divvy ($75 for a year) than the el ($100 for just a month). The three-speed bikes are also minutes faster than the elevated trains, according to a study by the urban transportation site Transitized of the top 1,000 Divvy journeys. With this year’s expansion to underserved areas on the south, west, and northwest sides, Chicago’s public-private network became the largest bike-share program in North America. From 69 stations and 700 bikes at its 2013 launch, Divvy now boasts 469 stations and 4,760 bikes. Before the expansion, 300 stations served 19 percent of Chicago’s area and 33 percent of its population. Now, those figures have jumped to 38 and 56 percent, respectively. Divvy’s dominion will continue to grow next year when it adds 55 stations in Chicago, 12 in Oak Park, and eight in Evanston. Yes, the baby-blue bikes are clunky and not exactly stylish. Still, Chicagoans have embraced them: in the past two years, Divvy has logged almost four million rides.