A car with an automatic transmission should be placed in first or second gear, depending on how steep the hill is. A car utilizes the lower gears in order to avoid overusing the braking system.
With an automatic transmission, there are two other gears that are rarely used by people living in flat driving environments. The lower gears allow a transmission to limit the amount of power that is transmitted to the wheels. This allows a vehicle to slow down even while descending on steep hill. Second gear is used on moderately steep hills and can only be shifted into when the car is traveling under 50 miles per hour. First gear is used in more dangerous environments that require more drastic stopping procedures. First gear requires the car to be traveling at no more than 35 miles per hour before being shifting into. When the car reaches a flat road the transmission can be shifted back into drive.
The process of using a lower gear is called engine braking. If a driver does not use the engine braking technique on a steep hill, the brake system will be prone to being overused. This can cause a slue of different issues, such as completely wearing down the brakes and losing braking power.