Zipcar, a car-sharing program that charges members an annual fee to rent cars by the hour, has plans to expand its offerings on the Yale campus over the next year, said Matthew Malloy, the company’s vice president of university operations. Malloy said Monday that Zipcar, which currently keeps 22 cars on campus, may expand to up to 50 cars over the course of the academic year. Yale, he said, is one of the top-five growing car sharing programs on North American campuses today. The Yale Office of Transportation Options, which works with Zipcar in implementing its program on the Yale campus, states on its Web site that 1,500 people in New Haven are Zipcar members.