The key numbers are also listed on the back of the check-sized driver's license. The key digits can be used to identify additional information, requirements and restrictions.
The code number 171 is defined as follows: "Category C1, also valid for motor vehicles of category D with a maximum permissible mass not exceeding 7500 kilograms, but excluding passengers" In 1999, a total of 16 driving licence categories were introduced. Driving licence class D entitles people in Germany to drive buses on public roads.