Awful Washington Traffic Has Brought Back Carpooling. Just Don't Talk Politics

Can't get over paywall, but from experience:

NoVa/DC Sluglines are a cool example of self-organizing communities. There is a set of informal rules and etiquette around passengers and drivers. A lot of it comes from the military background of the participants. The locations of pickup/dropoff sites were largely spread word of mouth in the pre-social media days.