What is the primary purpose of a parking brake?

The primary purpose of a parking brake is to secure a vehicle when it is parked. This brake is designed to hold the vehicle in place, preventing it from rolling away due to gravity or external forces, especially on an incline. It is a crucial safety feature that provides an additional layer of security, ensuring that the vehicle remains stationary when not in use.

While improving fuel efficiency, assisting in engine start-up, and controlling tire pressure are important vehicle functions, they do not pertain to the specific role of the parking brake. Fuel efficiency relates to how the vehicle operates while in motion, engine start-up involves the ignition system, and tire pressure is maintained through the use of specific inflation methods and monitoring systems. Therefore, the correct answer emphasizes the essential safety function of the parking brake in securing the vehicle when parked.