Major car-sharing companies Flexcar and Zipcar announced yesterday that they plan to merge. Zipcar, the larger of the two, has had strong growth mainly in large cities on the East Coast; Flexcar is more widely available on the West Coast. In both schemes, members can reserve a car over the phone or the interwebs, generally at a cheap hourly rate, then return it to its same location. Gas, repairs, parking, and insurance are all covered; a survey of Zipcar members indicates that they save some $5,000 a year by car-sharing instead of owning a vehicle. The new car-sharing company — to be called Zipcar, disappointing those of us who think ZipFlex sounds much saucier — will have 180,000 members with access to 5,000 vehicles in 48 cities.