Beijing was once a city of bikes, the capital of a country known as the Bicycle Kingdom for the millions of two-wheelers that dominated urban transport in a state-planned economy where cars were reserved for official business and the politically powerful. Decades of remarkable economic growth, beginning in the 1990s, led to a huge influx of cars in cities like Beijing. As the economy roared, autos pushed bikes off the roads, creating heavy pollution and miserable traffic. Now, Beijing may be returning to its roots. Thanks to about two dozen technology start-ups, brightly colored shared bikes have flooded Beijing since last year, dotting a normally drab cityscape with flashes of bumblebee yellow, kingfisher blue and tangerine. Commuters pick up the bikes and then ride and drop them off anywhere they like, locking the back wheel, with no need to find a stand or retether them. Costing as little as 7 cents a half-hour and designed to take people the last leg from public transport to their places of work or entertainment, the bikes have the potential to transform urban living and even shape people's decisions about where to live and work. Those are vital issues in this sprawl of about 20 million people, many of whom spend hours a day commuting. Having a bike like this might allow me to choose, say, to live a bit further out, or take another job in a place that isn't as easy to get to," said Ms. Cao, [an] employee at [an] advertising agency.