Yup I drive there too after I get off work since I don’t live close to the trail. I usually park in Sherlington at the Barcroft Community Center in Barcroft Park (4200 S Four Mile Run Dr, Arlington, VA 22206). They have a parking deck so I just leave my car in there, and then the trail is on the other side of Four Mile Run Dr. There’s a cross walk and a light so you don’t have to worry about dodging traffic 🙂
When you get on the trail, go to the left. The right takes you to the start of the trail, which is about 0.5 miles down the road. Happy riding!