It's that time of year when travel peaks for the holidays. For those of you traveling alone in the USA, here is an especially important reminder:
Not all unmarked cars with flashing lights are really police.
It is not safe to pull over in a deserted area/highway. There are some people who will pose as police to snatch you, rob you, or do worse. You are allowed to pull off at an exit and find a public area--gas station, restaurant, etc--to pull over, where you will be safer if the officer is a fake. The police are required to respect your right for safety, especially for women who are alone when being pursued by an unmarked car. Flash your headlights/taillights or emergency flashers to acknowledge the officer (so that they don't think you're trying to run); use some method of communication to let the officer know that you do intend to pull over, just in a safe place.
You are also permitted to dial 911 to get confirmation as to the validity of the officer, or even to have the dispatcher tell the officer of your intentions to pull over in a safe place. Some states also have a #77 or *77 state trooper line, sometimes intended for reporting other drivers' erratic or unsafe behavior, but this is NOT universal (in spite of some rumors). 911 is a much better choice and guarantees your call will be recorded. For other countries, dial whatever number is used as the standard for emergency police.
Be aware, of course, of laws against driving while using a handheld cell phone. No need to complicate matters!
If you have to pull over on the side of a road where you don't feel safe, keep the doors locked and only crack the window enough to be able to hear the officer through. If the officer insists on otherwise, you can explain your discomfort/concern for safety, and ask to travel to a safer location to continue, or dial 911 for the confirmation and ask for backup officers if necessary for proof.
If the car trying to pull you over isn't legitimate, these things may save your life.
Be smart, stay safe, drive carefully, and have a good holiday!