Start:  Roosevelt Island parking lot (or anywhere on the loop!)
Distance/Terrain:       about 18 miles/mostly flat

Left    onto Mt. Vernon bike trail (south - heading down river)
        there will be lots of side trails - stay on the Mt. Vernon trail !!
        just past National Airport
Left    take trail underpass _ this will connect to Four Mile Run trail
        follow trail along Four Mile Run creek
        you're now on the Wayne F. Anderson Bikeway
        pass wastewater treatment plant (really!!)
        trail will go under Mt. Vernon Ave.
        pass Arlington Ridge Road
Left    at stoplight, left on West Glebe Road, stay on sidewalk
        over small bridge
        *** follow green bike route signs
Right   Valley Drive
Right   Martha Custis Road
Right   at stopsign (Gunston ?) onto sidewalk
Right   onto pedestrial / bike overpass over I-395
        *** watch for sharp turns!!
Right   at end of overpass onto 28th Street
        you're now in Shirlington
Right   Quincy Street
Left    Four Mile Run bike trail (along Arlington Mill Road)
Right   Walter Reed Drive
Left    W&OD bike trail
        stay on W&OD / Four Mile Run bike trail 
        will cross George Mason  Dr. & Columbia Pike
        pass Arlington Boulevard (route 50)
        pass Wilson Blvd.
Right   Custis (I-66) bike trail
        *** don't miss this turn; there's a water fountain & bench at the turn
Left    at stop sign on trail
        cross under I-66
        stay on Custis Trail - there will be lots of side trails, ignore them
        the Custis Trail follows I-66 and crosses it several times
Cross   end of Custis Trail; cross Lynn Street onto sidewalk / bikepath
        follow bikepath as it crosses over the GW parkway
        back to the Roosevelt Island parking lot