What should you do when you notice someone driving erratically behind you?

Answer 1

Let him or her pass you and position your vehicle with plenty of space behind the bad driver.

Then, pull off the road and call the police. Give information like make-model and color of car, highway-road name or route number, direction (N-E-S-W), mile-marker or nearest Exit number, and anything else you can tell them. If you do not have a cellphone, many highways have "Call Boxes" every 1 to 3 miles (usually) for emergency services.