What must you do to prevent a two-axle bus from rolling down a slope?

To prevent a two-axle bus from rolling down a slope, you must engage the parking brake and place a wheel chock under a rear wheel. The parking brake alone provides the main braking force when the vehicle is parked, especially on inclines. However, for large vehicles like buses, using a wheel chock as an extra safety measure is required to physically block wheel movement, offering additional security against rolling. The bus-stop brake is only meant for securing the bus temporarily at stops, not for parking on slopes. Always use both the parking brake and a wheel chock for parking a bus safely on a slope, as required by German traffic regulations.