The ten parking spaces being set aside for Zipcars in Boston’s Columbus Center project will be yet another addition to a system of rental cars scattered through neighborhoods in the Boston, New York, and Washington metropolitan areas. Since 2000, when Robin Chase and Antje Danielson founded Zipcar in parking-short Cambridge, Mass., the company has deployed about 120 cars in the Boston area. Approximately 4,000 Boston area residents have agreed to pay a $75 annual membership fee or a $30 monthly fee. The vehicles — mostly Volks-wagens, Toyota Prius hybrid gasoline-and-electric cars, BMW Mini Coopers, and others with a certain style — are stationed in neighborhoods, at universities, and in other, mostly urban locations. A member logs onto the Internet to see what vehicles are available nearby, then reserves one, walks to it, and drives off, typically paying $6 to $8 an hour plus 40 cents a mile. “Architects use it for visiting clients; individuals use it for shopping,” says Nancy Rosenzweig, vice president of marketing. “You don’t usually take them on vacation.” Rosenzweig says the concept works best in dense cities possessing good transit systems — places where a person doesn’t need a car every day. Since the rental car is close by, it becomes an effective way to reduce the number of vehicles per household, she says. “Each takes about seven to 10 cars off the road,” she estimates. For more information, visit www.zipcar.com/. Zipcar and a competitor, Flexcar, are examined in an incisive report, “Selling Part of a Car,” by Aaron Donovan, in the recently published second issue of The Next American City. Flexcar rents cars by the hour in Seattle, where the company began in 2000, and in Portland, San Francisco, Los Angeles, San Diego, and Washington, DC. For more, click on www.americancity.org.