Final answer:
The correct actions after stopping a tractor-trailer are to engage the emergency brake and maintain enough brake pressure to keep the vehicle stationary, which is option D. both B and C.
Step-by-step explanation:
After stopping a tractor-trailer, the correct actions to take are to engage the emergency brake and also to maintain enough brake pressure to keep the vehicle stationary. Therefore, the answer is D. both B and C.
Engaging the emergency brake is a safety measure that ensures that the vehicle remains stationary, especially if the primary braking system fails. Maintaining sufficient brake pressure is also essential for keeping the vehicle from moving, providing an additional layer of safety.
It is important to mention that one should not pump the brakes after the vehicle has stopped because this could actually deplete the air pressure, leading to a potential safety hazard, as the truck relies on air pressure to maintain effective braking force. Furthermore, the truck brakes do work to control speed on downhill runs by converting gravitational potential energy into increased internal energy (higher temperature) of the brake material, which can be a risk if not properly managed.