To the best of my knowledge, all of the trails in the area are limited to day light hours only. The Park Police gives some lee way to commuters unofficially, but there are exceptions when they do crack downs. That's how I got my "after dark" ticket. To be fair to the Park Police however, one of the neighborhood gangs had recently dumped a body right off the trail I commuted on at the time so they apparently thought a crack down was in order. I have ridden parts of the Anacostia Tributary Trails, but not the Capital Cresent. I live in the Langley Park neighborhood of Silver Spring and work at 16th St. NW and M Street so most of my bike riding is on the eastern side of D.C. The trails are nice, but when commuting, the bike lanes on the streets are faster.

I'm glad you enjoyed your time in D.C. During the last few years, the city has made great efforts to become a bike friendly city and I think it has paid off for them. Don't disparage New York City riders too much, we have our share of ******** too.