Washington DC is really a particular kind of place. As much as everyone there is from somewhere else, a culture develops very quickly, and woe to the person who does not fit in.
At the airport in Milwaukee, I take the escalator from the lower level to my terminal. I stand wherever I want on the escalator. No one is rushing up unless they are seriously late for their flight, in which case it won't be the escalator that slows them up, it will surely be the folks at TSA.
And when I arrive at BWI and take the escalator down to catch my bus, I make sure to stand on the right side. Anyone loitering on the left should know better, despite the fact that there are no signs anywhere indicating this unspoken rule. But at BWI, people who want to walk on the left are polite, because they rightly figure that many of us are coming in from other places.
But on arriving in DC, there is absolutely no standing on the left side of the escalator. Anyone who does is looking for trouble. The words "excuse me" may be read politely on the page (or in the blog), but when someone says them to you on the Metro escalator - beware. They are about 2 seconds away from trampling you or shoving you to the right (and correct) side.
Metro has gone through various attempts to communicate the "walk on the left, stand on the right" culture, and inevitably they give up. There have been on the sides of the escalators, and for a while there were hideous big yellow circles on the floor with "walk left, stand right". My biggest gripe with those was with their grammar. I know what they were trying to say, but it sounded wrong. It would sound better if it said "walk left, stand correctly." Even though I know that's not what they were trying to say. Either way, the circles are gone....