No one really hitchhikes anymore, right? Well, in some places hitchhiking has evolved. You're no longer playing Russian Roulette by picking up a stranger, you're getting to work faster.
Those of you who live in the D.C. area will probably be familiar with slugging. It's an interesting example of spontaneous order in which drivers allow strangers into their cars to meet the carpool lane's vehicle occupancy requirement (in this case, HOV3).
Rules have evolved. No talking, for instance. Which makes sense because if people felt pressure to strike up a conversation with a stranger (particularly in the morning) it would probably make commuters less inclined to participate.
There's also an element of chivalry. Women are not to be left alone in a slug line.