[202_Cyclist]

yeah215-- I also live in DC, although I have never used ZipCar. The current Director of the DC Department of Transportation was previously a manager of Zipcar.

Zipcar can help decrease vehicle miles traveled. If motorists have to pay by the hour for each trip, then people will more likely use other modes of transportation for trips where a vehicle is not necessary. If a person owns a car, on the other hand, they only pay the incremental costs of gas and vehicle wear for each additional mile. This encourages drivers to use a car for short trips. Zipcar's fleet is usually newer vehicles that get better fuel mileage than other cars. Additionally, as this article notes, Zipcar has dedicated parking, decreasing the need to cruise for parking, which leads to more fuel consumption and congestion (pointed out by Donald Shoup).