At 60mph you are covering 88 feet per second. If the truck in front ran into something, or even braked sharply while you are 40 feet behind, even if you are blessed with the reactions of a cat there is only one outcome - you will make contact! The actual reaction time and the efficiency of your brakes will decide how hard the impact is!

Open a bigger gap, improve your visibility, protect yourself from all the dangerous drivers on the road, and save a life - maybe your own.