Zipcar is a car-sharing club founded in Cambridge, MAssachusetts, in 1999. The club members pay an annual fee and thn have the opportunity to rent a small car (usually a subcompact; the models include the Toyota Prius) for a fixed hourly rate. Zipcar is located largely in select metropolitan areas such as Boston, San Francisco, and Washington D.C, called "Zipsters," make reservations for a car on the Zipcar website and then use an access card to open the vehicle. The vehicle has a "home base" parking spot where the driver picks up and returns the vehicle. The club - which, as of early 2017, operates in more than 500 cities and towns, at more than 600 college campuses, and 50 airports - has grown to more than 1 million members since its initial public offering in April 2011.

1. What are the fixed and variable costs for Zipcar?

2. What are some of the competitive advantages and challenges of the Zipcar concept?