Hey Terry...
If I have to travel over 30 minutes to a job, I determine what I average every hour I work and try to throw the driving time into my estimate. If this becomes too high, I give a moderate increase to my price, then try to arrange for another job to be done as near as possible. It's also good to ask the householder if they know anyone who is interested in having their windows clean. If they can find someone, I tell them I will waive the gas cost increase.