The loaded parking is just not released, you will need your intervention in Parking Polly Cars. Transport is close to each other, you need to carefully inspect the location of the cars from above and determine the car that can be removed without problems. Click on it and direct it in the right direction. In some cases, you will have to move the car in the parking lot to give the neighbor to leave. Each next level will be more complicated, there are more cars, as well as fencing items in Parking Polly Cars will be added.
