@nevermore1701 - I know a lot of fellow Virginians who feel that way, but I think they are being silly.

@ R88 - The areas songfta mentions are all fine at night, especially if you stay on the main roads and use common sense. You can always go into town for an evening, then take Metro back to Greenbelt to avoid more remote neighborhoods and getting lost in the dark.

Here is the route, mostly trail, from Greenbelt Park into DC.
http://www.gmap-pedometer.com/?r=5669414
This takes you past the Greenbelt Metro. Lake Artemesia is a nice park and from there you can take the Paint Branch trail to College Park. Once you get off the NW Branch at 38th you are on mostly good streets (paving a little rough just before the DC line) and generally good neighborhoods. At mile 11 you can turn at 8th street and switch to the Metropolitan Branch Trail, but Eckington is a pretty neighborhood so you should try 4th at least once.

Here’s a loop through the Agricultural Research Facility to Bowie. It’s been a couple of years since I’ve ridden it, so I’m not sure of the condition of all of the roads, especially Beaver Dam. But it is a pretty area to ride.
http://www.gmap-pedometer.com/?r=5669849

Songfta mentioned Silver Spring Here is a mostly trail route starting from NW Branch
http://www.gmap-pedometer.com/?r=5670420

If you need any specific information about routes, destinations, upcoming events, etc. feel free to PM me.