As a software consultant, one piece of advice I often give to companies developing software is that they have to increase their bus count. The bus count is the number of people on the team who need to be run over by a bus in order for the project to fail or be incur a serious cost or delay. If you have a bus count of one, then only one person knows how some critical portion of the system works and is able to maintain it. If that one person is hit by a bus, you have a serious problem dealing with that portion of the system.

The best solution for a lot bus count is pair programming because it distributes the knowledge of the system to several people (especially with the XP policy that the pairs keep switching and working on different parts of the system).

I often use the term "bus count" but I've forgotten where I heard it from. I googled and found one reference to it on Craig Murphy's blog, so I know that other people have heard the term. It seems to me like the kind of term that came out of Extreme Programming, but I can't quite place it. Does anyone know where the term came from? Am I nuts and I'm the only one who uses it? I don't think so.