Tokyo housewife Chie Igawa, 38, is part of a trend that's transforming the streets, zipping her kids around on a battery-boosted bicycle without breaking a sweat or having to worry about traffic rules.

Domestic sales of the bikes eclipsed those of scooters for the first time last year and have jumped 24 percent since January, according to the Tokyo-based Bicycle Promotion Institute. In 2008, Yamaha Motor Co. sold more of the bikes in Japan than motorcycles. Rival maker Panasonic Corp. predicts the market will triple to a million units a year.

"I started riding it a few months ago," said Igawa, pausing on a sidewalk near the Imperial Palace, with her two boys strapped into child seats. "You couldn't do this on a moped, it would be illegal."