What must you do when transporting bicycles on the roof of your car?

Your answer is correct because German traffic rules emphasize safety when transporting bicycles on the roof of a car. First, you must securely attach both the holding device and the bicycles to prevent any risk of falling or shifting during the journey. Second, it is important to avoid high speeds, as increased speed can affect vehicle stability and increase wind resistance, posing danger. Third, regularly checking the fixing devices ensures that everything remains tight and secure throughout the trip, preventing accidents. Following all these steps helps guarantee safe transport and compliance with traffic regulations.