 Never use cruise control when operating in adverse driving conditions, including wet, icy, or slippery roads, during rush hour in heavy traffic or on congested highways, at night, or when you're tired or fatigued. During all of these driving scenarios, you want to be controlling and adjusting your speed as you drive instead of having to suddenly brake if you encounter an obstacle. In the case of a slippery road surface, you want to be able to slow your vehicle by not accelerating instead of using the brakes whenever possible.