When the road is slippery, you should keep much more space in front of your vehicle.
Large, heavy vehicles have long braking distances. On slippery roads, the braking distance will be even longer. Make sure you leave an adequate following distance behind the vehicle ahead of you. The formula for following distance under ideal conditions is one second per ten feet of vehicle, plus an extra second if you are traveling over 40 mph. On slippery roads, increase your following distance even more.