New Slugger

I will be temporarily living in Locust Grove Rt 3 and need to catch on to the "slugging" routine. I looked at the map at the commuter lot at Rt 17 but not understanding how to actually get there. Do I have to exit from Rt 3 on to 95 going south or north and exit again on to 17? This first time feeling of "slugging" feels like taking a trip across Europe, alone. Also, if I have to be at work by 7:30am in the city, what time should I be at the commuter lot?

In case you didn't see this, this is the message intended by JP:
Take I95 North from Rt.3, go about 3 miles north to Rt. 17 and take signs towards Warrenton. Commuteride lot is about 1/4 mile down Rt. 17 from I95. Turn left at light (Pizza Hut and East Coast will be on the right side of Rt. 17) and you are in the lot. Slug line forms at the bus shelters. You should give yourself at least one hour to get into DC. Depending on where in DC you work, the time may be more/less.