It's enforced in DC, although I suspect it's partly because of the absurd numbers of bike messengers who would use sidewalks as obstacle courses. On the other hand, I think riding in the road in DC is relatively safe because there are so many bike messengers. Most drivers learn to drive cautiously when sharing the road with cyclists who are fast, aggressive, and potentially dangerous if cut off.
Biking in DC is insanely dangerous, and the cyclists here are some of the worst I have ever seen. There is some kind of massive and fundamental lack of recognition that they should at least try to follow some of the traffic laws, sometimes, if they want to be taken even a little bit seriously. More than once I've nearly been taken out by a cyclist who wasn't expecting me to do something crazy and unpredictable, like stop at a red light or yield to pedestrians.
If you expect drivers to yield to you, give you your lane, and (most importantly) not actively work to bring about your death, you can't be weaving in and out of traffic, running red lights, or not letting cars through to turn at intersections. Even if you don't give half a damn about your own life, it's just simple courtesy.
In general, people on bicycles in DC combine the worst parts of the "urban road warrior" cyclist stereotype with the intense sense of entitlement and privilege shared by most in the DC area: "why the fuck should I stop at a red light? I have places to be. I saw David Axelrod at Ruth's Chris yesterday. Do you know who the fuck I am?"
The drivers are insane as well, but I want to grab most of the cyclists I see around here by the shoulders and shake them hard: "Do you want to die??!? DO YOU??!!!?" They are just the worst and sicken me deeply every day.
Cycling anywhere in the US is dangerous. However, I think many people mistake the feeling of danger for actual risk. DC cyclists make drivers incredibly uncomfortable, which means they are paying attention. As a cyclist, it's better for drivers to be cursing you than to not see you. Not that that's an excuse for not stopping at red lights.
In DC it's only illegal to ride on the sidewalks in a very specific, downtown business district that's marked by a lot of pedestrian traffic.
I wouldn't say it's all that safe on the street in DC. I've very nearly been run over by cars (especially cabs) that want to turn right out of a circle (which even has a bike lane).
