Hi Mary:
Living in Denver, I don't charge travel for anything inside the "Denver Metro Area". Now, living in Manassas, you may want to consider not charging for the "greater Washington D.C. metro area", although, a trip from Manassas to the other side of the beltway is quite a trek.
I charge .35 per mile plus $25 per hour of my time - factored into the cost of the portrait. Have never had to charge it, but I know what to say if it ever comes up.