I've never done it, so this is all what's been explained to me. We have a bit of a traffic problem in DC. OK, more than a bit. So naturally people have gotten pretty creative to deal with this. To help with the traffic congestion in the area, we have carpool lanes, which allow you access to faster lanes if you have more than one person in the car (and sometimes more than 2). But what if you don't a buddy to carpool with? That's where slugging comes in.
From what I've been told, you drive up to some lot, relatively close to your house. You then pickup a perfect stranger and drive into work. You drop off the stranger at another relatively well known location. Then on the way back to work, you repeat. Again, most likely picking up another stranger.
We have a name for this besides slugging - it's called hitchhiking. As far as I know, the government (local or otherwise) doesn't do anything to monitor it, nor do they do anything to stop it.
I find this program absolutely remarkable. We live in a country where you aren't supposed to trust anyone with anything. Every promise and action we take comes with the warning that you can get sued, so you're better off not promising or acting. And yet somehow, in our nobody-knows-their-neighbor-or-cares society, you have perfect strangers giving each other a ride to work. The whole system appears to be a bottom up system that just works.
I just love that this system works. It gives me hope in society, in people's abilities to trust one another and in our ability to find novel solutions to really tricky problems. Bravo!