What is the effect on a truck-trailer combination when the parking brake in the towing vehicle is engaged (not in the test position)?

In the context of a truck-trailer combination, when the parking brake of the towing vehicle is engaged, it primarily serves to secure the towing vehicle and prevent it from rolling. This means that the towing vehicle will be mechanically braked.

For the trailer, under normal circumstances, unless additional measures are taken, it is not mechanically braked. Instead, it relies on the service brake system, which operates using compressed air. This means that while the towing vehicle is secured, the trailer may not have the same level of security unless the service brake system is also engaged.

Understanding this distinction is important for safe loading and parking practices. Properly engaging both the towing vehicle's parking brake and ensuring the trailer's brakes are also functional is critical to prevent unintended movement, which is especially relevant under German traffic regulations aiming to enhance road safety.