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The 21st-century equivalent of the cavalry has come charging in to rescue cities in China and South Asia in their battles against air pollution and global warming. And it's also beginning to help out on the traffic-choked streets in London, New York, São Paulo and Los Angeles.
This is the electric bicycle, or "e-bike," a technology that blends the simplicity and mobility of a traditional bicycle with the speed of a moped or motorized scooter, but without the internal combustion engine.
Transportation experts say e-bikes -- along with electric cars, light-rail trains and more pedestrian-friendly cities -- could become one of the primary drivers of cleaner air and reduced global greenhouse emissions across much of the urbanized world, with China, India and Southeast Asia leading the fight to clear the air.
"The bicycle is an enormously efficient vehicle," said Ed Benjamin, managing director of eCycleElectric, a consulting firm to the light electric vehicle industry with offices in the United States, China and Taiwan. "The rolling resistance is minimal. They cost very little in terms of materials and the energy needed to build them compared to other vehicles. They don't require gasoline and can be parked almost anywhere."
"The problem," Benjamin added, "is we could say a bicycle is only good for healthy, strong people who are willing to get out in the weather. And there are large populations around the world that don't fall into that category."
Still, e-bikes -- defined as two-wheeled vehicles equipped with a traditional bicycle drivetrain but enhanced with an electric motor capable of propelling a bike as fast as 20 mph -- have solved the mobility problem for hundreds of millions around the world.
In China alone, more than 100 million e-bikes have been sold over the past decade, accounting for "the single largest adoption of alternative fuel vehicles in history," said Christopher Cherry, a University of Tennessee engineering professor and leading scholar on e-bikes.
In addition to being light and relatively inexpensive, e-bikes are also more climate-friendly than other modes of transportation, including gasoline- or diesel-powered cars and buses, and even electric passenger vehicles. In fact, carbon dioxide emissions for a Chinese e-bike are about one-tenth of what is emitted by a conventional electric car, when factoring in the electricity source needed to power the car's much larger batteries, according to research published recently by Cherry and colleague Shuguang Ji.
Yet despite their many positive attributes, e-bikes have been slow to win favor with consumers outside Asia, and they represent a tiny fraction of total U.S. bicycle sales. In the United States last year, official tallies show e-bike sales of 80,000 units, according to data compiled by Electric Bikes Worldwide Reports. That compares to 30 million e-bikes sold last year in China, 1.4 million in India, 400,000 in Europe and 300,000 to 350,000 in Japan.
Pedal-prone people grow older
While no two countries or regions have the same set of factors driving the adoption of e-bikes, most share a few things in common -- namely urban congestion, a lack of sufficient parking for cars and a cultural acceptance of two-wheeled vehicles as a viable form of daily transportation.
Throughout much of Europe, where the modern bicycle was invented in Germany around 1818, "the population is generally getting older and less mobile, but these are people who have ridden bicycles their entire lives," said Benjamin. "So the idea of being able to go longer distance at faster speeds, but still doing it on a bike, has broad appeal."
China's e-bike explosion dates to the mid-1990s, when large cities like Beijing and Shanghai adopted strict anti-pollution measures to alleviate some of the world's worst urban air quality. The country has its own cultural bond to two-wheeled transit.