Here is good advice from Mothers Against Drunk Driving (MADD) from their web site at wwww.madd.org:
First, stay as far away from the other vehicle as possible.
Second, do not try to pass the vehicle or signal the driver to pull over. Doing so could result in a collision.
Third, take notice of the license plate number of the driver along with details of the vehicle including make, model and color. However, make sure you don’t compromise your own safety trying to obtain this information.
Finally, pull over and call 911. Give the exact location of the vehicle, including the name of the road or cross streets and the direction the vehicle is traveling. Give a complete description of the vehicle and the manner in which the vehicle is being driven.
Then leave the rest up to the heroes that work hard to make our roads safe.