Crash features about two dozen characters with interlocking stories all brought together by fate. It's a technique used by many films in the 90s, like Pulp Fiction (1994), Go (1999), Short Cuts (1993), and Magnolia (1999). Crash takes it to the next level.
Another narrative trick Crash uses is to start at the end, then flashback to "yesterday" and finish at the beginning. This device sets up Detective Waters as the film's main character, even though he is only one of many.
Nevertheless, almost every other character's storyline intersects with Waters'. He is Peter's brother, who is shot by Officer Hanson. He and Ria crash into a woman who is related to the man run over by Anthony and Peter. And he has a tense encounter with Flanagan, who works for Rick Cabot. The only person he doesn't interact with is Ruiz, though Ruiz is only one degree of separation away.
We do think it's funny, though, that in a movie with interlocking narratives, it's the locksmith who is the one on the fringe…