What should the parking brake be designed to do once applied?

The parking brake is a critical safety feature designed to secure a vehicle when it is stationary. Once applied, it should remain engaged to prevent the vehicle from rolling or moving unintentionally, regardless of the status of other energy sources or systems in the vehicle, such as the engine or transmission. This ensures that, even if there is a failure in the primary braking system or the engine is turned off, the parking brake continues to hold the vehicle in place.

This characteristic is essential for safety, particularly in scenarios where a vehicle is parked on an incline or slope. If the parking brake were to release automatically after a few minutes, it could lead to dangerous situations, as the vehicle could roll away without any warning. Similarly, the other options imply limits or immediate control measures that don't align with the primary purpose of the parking brake, which is to provide a secure hold until the driver is ready to move the vehicle again. Thus, the correct design requirement for a parking brake is to remain applied without reliance on any energy source.