Traditional cruise control systems do not have a built-in mechanism to prevent the vehicle from going over the set speed limit when going downhill. Cruise control is designed to maintain a constant speed on level terrain by adjusting throttle input. When the vehicle goes downhill, gravity can cause it to accelerate beyond the set speed limit because the cruise control system does not actively apply brakes or reduce engine power to counteract the increased speed.
However, some modern vehicles may feature advanced cruise control systems, such as adaptive cruise control or intelligent cruise control, which incorporate additional sensors and technology to mitigate this issue. These systems use radar, lidar, or cameras to detect the distance and speed of vehicles ahead. They can automatically adjust the throttle, apply brakes, or downshift gears to maintain a safe following distance and prevent the vehicle from exceeding the set speed limit, even when going downhill.
It's important to note that the specific functionality and features of cruise control systems can vary between different vehicle manufacturers and models. Therefore, it's always advisable to consult the vehicle's owner's manual or contact the manufacturer to understand the precise capabilities of your vehicle's cruise control system.