What is the purpose of 'Wheel Chocks' (Unterlegkeile) carried on heavy passenger coaches?

1. To supplement the parking brake during every ordinary level-ground stop, without checking the vehicle procedure
2. To place in front of any convenient wheel without considering the slope direction
3. To support the vehicle during a wheel change without approved lifting or support equipment
4. To mechanically block the wheels and prevent the vehicle from rolling away on steep inclines during parking, breakdown stops, or wheel changes