AJsinVA’s map looks like it takes you on the 4 Mile Run Trail from Shirlington to Glencarlyn instead of the W&OD. Where Google routes you depends on the way points you put in. It was actually difficult to get it to take me from 4 Mile Run to the W&OD at Shirlington, but I just move a way point and got there. This gives the distance as 15.7 miles with a starting and ending point at the N Lynn St intersection with the Custis Trail. Before the I-395 underpass on 4 Mile Run was completed, the distance was about 16.5 miles.
http://maps.google.com/maps?f=d&source=s_d&saddr=Custis+Trail+and+N+Lynn+St,+arlington,+va&daddr=Mt+Vernon+Trail+to:Washington+and+Old+Dominion+Railroad+Trail+to:S+Walter+Reed+Dr+%26+S+4+Mile+Run+Dr,+Arlington,+Virginia+22206+to:bon+air+park,+arlington,+va+to:Custis+Trail+and+n+lynn+st,+arlington,+va&geocode=FXONUQIdXv5n-ymdk5LYWra3iTFrZUtEQRP0zA%3BFU7XUAIdT1to-w%3BFRrAUAIduqNn-w%3BFfPBUAId8Z5n-ylR-GDCU7G3iTHIEMi1f44rjQ%3B%3BFXONUQIdXv5n-ymdk5LYWra3iTFrZUtEQRP0zA&hl=en&mra=ls&dirflg=b&sll=38.87767,-77.127628&sspn=0.065883,0.110035&ie=UTF8&ll=38.870053,-77.08849&spn=0.06589,0.110035&t=h&z=13&lci=bike
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