I have never commuted from up there, but I would take Broadway Branch Road until you can get on to the bike path that runs parallel to Beach Drive. That will take you far enough south so that you can turn off and take the P Street bridge. Cut up 22nd Street to Q. Take Q all the way to 15th Street, turn right (south), and taking that all the way past the White House to G Street. Turn left on G and you’ll be in Chinatown in 10 blocks.
That commute will probably take you at least 40 minutes but it’s going to be pretty safe.
Here’s the map: http://www.gmap-pedometer.com/?r=5612653
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