Hill descent control system
Hill descent control (HDC, or hill mode descent control) is a driver-assistance system. It allows a controlled hill descent in rough terrain without any brake input from the driver.
Overview
When on, the vehicle will descend using the anti-lock braking system (ABS) to control each wheel's speed. If the vehicle accelerates without driver input, the system will automatically apply the brakes to slow down to the desired vehicle speed. Cruise control buttons can adjust the speed to a comfortable level. Applying pressure to the accelerator or brake pedal will override the HDC system when the driver requires.
Land Rover originally developed HDC for use on their Freelander model which lacks the low range gears usually provided on 4x4 vehicles. At the time it was derided by enthusiasts, and many claimed its set speed was too high for a controlled descent in difficult conditions. Despite the critics, the system was a leading-edge technology and allowed the Freelander, coupled with the traction control system, to be renowned for astounding offroading performance that set it apart in the category of the so-called "soft roaders" produced in the 90s. Later implementations such as the Range Rover and Discovery combine HDC with traction control and low-range gears, and also have reduced the set speed to slower than walking pace for extra control.
Four-wheel drive (4WD) and all-wheel drive (AWD) vehicles, such as Ford Territory, may have a hill descent control system installed, using the ABS to control the car's motion downhill, initially developed by Bosch for Land Rover. The system can be controlled, usually by the cruise control buttons near or on the steering wheel.
Renault / Automobile Dacia has recently added Hillside Decent Control in the second generation of the Dacia Duster, making it the most affordable vehicle in it's segment with Hillside Decent Control.