I set the vistors to zero like ZapWizard said. Also I put some more information in the description of the workshop Item. I don't know if its work better now because I haven't tested it yet.

To place this so that people will actually park in the garage, place it slightly down-stream of a highly visited location such as a stadium. The Cims seems to prefer to disembark near an intersection. In the video that I made and Bucksmith referenced below, the Cims are forced to disembark with the garage between them and their destination (a bus stop). They wouldn't use a garage on the opposite side of the road for example.

Another way to determine a good location is to look where people are parking in the side of the road.