| This is the coolest thing. D.C. has some of the worst traffic in the nation right now, and to make it worse, Virginia's high occupancy vehicle lanes require three or more passengers (most states, Maryland for example, only requires two or more passengers) during rush hour.
Slugging is a response to this; basically, some person in a car picks up two complete strangers in order to use the high occupancy vehicle lane, thereby reducing a commute time by an hour or so. Except it's more sophisticated than that. For example, the Pentagon is one of the largest slugging stops - it has, say, five different lines, and each line of people are going to a different section of D.C.. So a driver going to that section picks up passengers from that line, and drops them off at a pre-arranged place in the city - usually a Metro stop.
The cool thing is that this is totally not official or organized. Everybody just seems to know which line goes where, and where the drop-offs and pick-ups are. There are other rules, too. A slugger cannot smoke or roll a window down, or even speak while in a stranger's car. A driver cannot turn the music up really loud. It's all part of the unwritten Slugging code of honor.
This may exist in other cities, I don't know. | 
