The **parking brake** is not designed to regularly slow down a moving vehicle. Its main function is to keep the vehicle stationary when parked. However, in **emergency situations**, it can be used to help stop the vehicle if the main brakes fail.

- The **engine brake** is a safer option to reduce speed without using the wheel brakes. It works by ceasing to accelerate, allowing the engine to hold the vehicle back, especially in low gears.

- For efficient and safe driving, it is recommended to lift your foot off the accelerator and use the brake gently to gradually reduce speed.

- The **brake pedal** is the appropriate device to slow down or stop the vehicle, as it acts on all wheels and should be used gently with the right foot.

Therefore, the use of the parking brake to reduce speed should be limited to emergency situations, as it is not designed for that purpose and could compromise safety.