Here is the information I got from the German tourist-board regarding using the blue parking-card for disabled:
- On roads and in car parks, parking places reserved for disabled people are marked with a wheelchair symbol. Do not park if the space is marked with a person’s name or vehicle registration number.
Parking on roads:
- You may park for up to three hours on roads or in zones where parking is otherwise prohibited.
- You may exceed the parking time on roads or in zones where parking time is restricted.
- You may park free of charge in parking places where payment is required through pay and display machines or parking meters.
- You may park in parking places reserved for residents for up to three hours.
- You may park in restricted traffic zones and outside the designated parking places provided you do not hinder through traffic.
- Park in pedestrian zones only if local concessions explicitly allow it. Check locally. Even if it is permitted, you are only allowed to enter and park at specified times.
Note: These parking concessions only apply if there is no alternative parking option available nearby. The maximum time limit for parking cannot exceed 24 hours.
You can also use your blue card at ordinary parking places with “pay per hour”, for free and past the limited time.
Visit Germany has a very good resource for disabled, please have a look!