Electric bicycles offer a new option.

* Electric bicycles offer a new option: Sales of electric bikes provided a small spark of life last year to a struggling global bicycle industry. Bicycle production has shown little growth in the last five years, but sales of electric bikes in 2000 tripled over those in 1999. More than 1.1 million sold last year, accounting for about 1 percent of global bicycle production. Commercially available only since 1993, electric bikes are proving popular among commuters in China and Europe, and among seniors in the United States, who use the vehicles primarily for recreation.

E-bikes, as they are sometimes called, allow riders to add more power to their pedaling by engaging an electric motor at the flip of a switch. On some models, the extra power is supplied steadily, while on others it is added only as the rider pedals. Unlike motorbikes--the heavier, usually gasoline-powered vehicles that resemble small motorcycles--electric bikes are standard bicycles that, with the aid of an attached rechargeable battery-powered motor, can reach speeds of 15 to 20 miles per hour without pedaling.

E-bikes are a promising addition to the repertoire of sustainable transport, because they make cycling more viable for workers who face long commutes, hilly terrain, or even hot weather that could otherwise leave a rider drenched in sweat on arrival at the workplace. And as electric bikes are substituted for motorbikes or cars, they have the potential to make cities cleaner and quieter.

Electric bikes tend to be expensive compared to conventional bikes, ranging from about $500 to several thousand dollars, although they are more affordable than motorbikes. Seventy percent of e-bike sales last year were made in China, where they are now a common sight on city streets. In the United States, e-bikes are, paradoxically, being produced by automobile manufacturers, and are often marketed through car dealerships as an incentive for luxury car purchases.

As research advances, e-bikes could become even more attractive as a mode of sustainable transport. Ed Benjamin, a consultant who follows the global electric vehicle industry, notes that as fuel cells have shrunk in size, they have been used to power bicycles on an experimental basis. Such an advance would combine the non-polluting character of conventional bicycles with greater power, making the bicycle a more widely usable mode of transportation.