To resolve my last post: It worked! I had booked a car from the car sharing company zipcar and I could unlock it with my zipcard. Fortunately, the tank was more than 1/4th filled up, because if not, you have to get gas - but the company pays for the gas, so you don't have to worry. But sometimes the car's credit cards don't work and you have to pay etc. lots of things could go wrong ;-)
The car itself was working great and it was mainly clean, too. It seemed to be useful for longer drives as well as it had a cruise control. I booked it for one hour and I returned it on time, so I didn't have to pay any additional fees. The total cost for the trip was 9.18 $. And after it took me such a long time to become a member, actually getting one of their cars is easy :-)
