Flexcar, Seattle's pioneering car-sharing company, is getting some competition.

Cambridge, Mass.-based Zipcar announced yesterday it plans to expand to the West Coast. CEO Scott Griffith said the company will start signing up members and renting cars in Seattle no later than the end of 2006.

Flexcar and Zipcar are the Coke and Pepsi of the infant car-sharing industry, but until now Zipcar has operated almost exclusively on the East Coast, Seattle-based Flexcar mostly in the West. The only market where the two now compete is Washington, D.C.

Car-sharing participants can reserve and rent cars parked near their homes or workplaces for an hour, a day or a weekend. The company takes care of gas, parking, insurance and maintenance.

Zipcar said yesterday that a $10 million infusion of new venture capital will allow it to go national, starting with operations in Seattle, Portland and San Francisco. The schedule for initiating service in each city will be announced Aug. 1, the company said.

Flexcar's response to Zipcar's announcement was diplomatic.

"It's a tremendous validation of the car-sharing business in and of itself," spokesman John Williams said. "It's coming out of the green, niche market and into the mainstream."

Flexcar has about 12,000 to 15,000 members and 150 vehicles in the Seattle area, he said. Zipcar's Griffith said his company plans to start here with at least 100 vehicles. Zipcar's research has identified a potential local market for 750 to 1,000 car-share vehicles in the near future, he added: "It certainly can grow substantially from where it is now."

Those numbers don't sound unreasonable, said Todd Litman of the Victoria Transport Policy Institute, a research center in Victoria, B.C. "We don't really know what the full market potential is," he said, "but it's possible 10 percent of urban households could rely on car-sharing for their only vehicle, or their second vehicle."

Seattle's relatively high taxi fares also could help car-sharing grow, said Rex Toh, a transportation specialist at Seattle University's Albers School of Business and Economics. In Singapore, he said, a car-sharing experiment failed in part because taxi rides were cheap.

Advocates tout car-sharing as an economical option to vehicle ownership for city dwellers who don't need a car to get to and from work but still like access to one for errands or out-of-town trips.

Some employers also have accounts with car-sharing firms.

Zipcar provides free satellite radio receivers in all its vehicles; Flexcar doesn't. Zipcar also has more makes and models available, including the Mini Cooper and boxy Toyota Scion xB. Flexcar rents mostly Honda Civics.

Griffith said those innovations have been well-received by Zipcar's members. Williams said Flexcar's approach is different. Car-sharing, he said, "is not necessarily meant to be cool, it's meant to be practical."

Eric Pryne: 206-464-2231 or epryne@seattletimes.com