Carry a weapon (handgun, pepper spray, etc) and maintain awareness of your surroundings. This works really well:
http://www.amazon.com/Sabre-Pepper-Jogger-Defense-Marking/dp/B000ALIREU
If you find yourself in some potential trouble, head directly for the most populated & well-lit area you can find nearby. Don't give anyone the impression you're easy prey.
Also, call the cops (FFX Co. Non-Emergency 703-691-2131) after such incidents with all the relevant details (descriptions, license plate #, time, location, etc). I've found that cops around here are very responsive (what else do they have to do really?).
Carry on, keep running, stay alert and you'll be OK.