By J. DAVID GOODMAN

SHANGHAI - Detroit may be introducing electric car designs and China may be pushing forward with a big expansion of its highways and trains. But delivery workers in New York, postal employees in Germany and commuters from Canada to Japan are among the millions taking part in a more accidental transportation upheaval.

It began in China, where an estimated 120 million electric bicycles now hum along the roads, up from a few thousand in the 1990s. They are replacing traditional bikes and motorcycles at a rapid clip and allowing many people to put off the switch to cars.

The booming Chinese electricbike industry is spurring worldwide interest and sales in India, Europe and the United States. China is exporting many bikes, and Western manufacturers are also copying the trend to produce models of their own. From virtually nothing a decade ago, electric bikes have become an $11 billion global industry.

“It’s miraculous - it takes the hills out of riding,’’ said Roger Phillips, 78, who rides an electric bike around Manhattan.

Electric bikes have been a “gift from God” for bike makers, said Edward Benjamin, an independent industry consultant, not only because they cost more - typically $1,500 to $3,000 - but also because they include more components like batteries that need regular replacement.

In the Netherlands, a third of the money spent on bicycles last year went to electric-powered models. Industry experts predict similar growth elsewhere in Europe, especially in Germany, France and Italy, as rising interest in cycling coincides with an aging population. India had virtually no sales until two years ago, but its nascent market is fast expanding and could eclipse Europe’s in the next year.

“The growth has been tremendous in the last two years,’’ said Naveen Munjal, managing director of Hero Electric, a division of India’s largest bicycle and motorcycle maker. He expects sales at Hero to increase to 250,000 electric bikes in 2012, from 100,000 in 2009.

While the American market has been modest - about 200,000 bikes sold last year, by some estimates - interest is rising, said Jay Townley, a bicycle industry consultant. Best Buy, the electronics retailer, began selling electric bicycles in June at 19 stores in San Francisco, Los Angeles and Portland, Oregon.

As the global market develops, two types of electric bikes are emerging. One is similar to a standard bicycle with pedals, but it has an electric motor that engages on command or when the cyclist pedals.

In China, electric bicycles have evolved into bigger machines that have small, wide-set pedals that most cyclists do not use as they travel entirely on battery power. The bikes can travel at speeds up to 50 kilometers an hour, with a range of 80 kilometers on a fully charged battery.

These larger models are causing headaches for global transportation planners. They cannot decide whether to embrace them as a green form of transportation, or ban them as a safety hazard.

In China, electric bicycles “have a moderating influence on the use of cars,’’ said Cornie Huizenga of the Clean Air Initiative for Asian Cities, an advocacy group.

For each kilometer traveled, electric bikes cause fewer emissions of the gases associated with global warming than do cars. But a typical Chinese model uses five batteries in its lifetime, each containing 10 to 14 kilograms of lead. In areas without stringent recycling programs, the potential for environmental contamination is high.

An electric bike rider is also more likely than a car driver to be killed or injured in a collision, and as the number of riders has soared, fatalities in China have risen. And riders of these vehicles often choose to take bicycle lanes, where they mix with slower-moving bikes and pedestrians, adding to the potential for an accident.

In New York and in parts of Europe, riders have reported harassment from regular bike riders when they use the lanes.

Jessy Wijzenbeek-Voet, 71, said she simply gets stares from other cyclists when she takes her electric bike to the store in the Netherlands. “They look at me wondering, ‘How is it possible that lady is going so fast?’ ‘’


Electric bicycle riders in China, where about 120 million such bikes are used, with some going up to 50 kilometers an hour. / J. DAVID GOODMAN FOR THE NEW YORK TIMES