Rear-end collisions are among the most preventable. By slowing down and keeping your distance, most people are able to avoid crashes by virtue of having enough time to stop.
Unfortunately, it's not always that easy for the person in front. Someone who is tailgating you or riding too close to your bumper may hit you, even if you try to speed up and give yourself more space. If you have to put your brakes on quickly, the likelihood is that they won't have time to stop.
Then, there are the cases where you're stopped at a red light or stop sign, and another person doesn't stop. They hit you from behind, sometimes at full speed, causing your vehicle to enter an intersection. At that point, there is a risk of a multi-vehicle collision as a result of their negligence.
What should you do if you see someone tailgating you?
One option is to slow down and to try to stop or get out of the way. If this doesn't encourage them to move to another lane, you can attempt to switch lanes or pull to the side of the road. Always slow down as much as possible before doing this, so that the other driver gets the idea that you don't like that they're on your tail.
The best thing you can do is to let a tailgater pass you if you can. This won't prevent every instance of a rear-end collision, but it will help you prevent one caused by someone who is following your vehicle far too closely.