and plan to walk around sightseeing, here's a simple tip - OBEY the walk/don't walk signs and be sure not to wander out into the street when the light is against you! It's a recipe for vehicle-assisted suicide!
The worst drivers in the world are in D.C. Forget the fact that there are numerous cars with diplomatic license plates (which essentially means they can run over your sorry ass with impunity), the city is supposed to be bicycle friendly which only means that people on bikes are incredibly arrogant and dismissive of the rules of the road, plus there are a lot of very weary people who commute unconscionably lengthy distances to come to work here who may just have slight moments of inattention. Add to the mix the plethora of independently owned taxicabs in the City (they are actually the most courteous component of driving in D.C.) and you have a recipe for peril.
I have never seen a city with so many heedless and careless pedestrians. This problem is most acute in areas dominated by government buildings (and government employees). They appear to believe they are somehow immune from normal safety concerns.
So bear this in mind - don't disregard safety laws when you come to the District for any reason. It's a dangerous place to be!