Los Angeles: where the racial tensions are bad, and the traffic is worse. It's the perfect place for Crash, a movie about road rage, racial rage, and just rage in general.
The movie isn't set in a particular time period, but it's definitely post-9/11. For one thing, it was made in 2004, but more importantly, the racial attitudes toward Farhad are at least partly a result of the Islamophobia that reared up after the World Trade Center attacks. Just get a load of what the gun clerk says to Farhad, for example:
GUN CLERK: Yo, Osama! Plan a jihad on your own time.
Although the movie isn't necessarily location specific, it would have been hard to set it in a different place. It needs to be a large city, but other cities, like Boston or New York or San Francisco, have a different kind of traffic problem: their traffic doesn't move. Los Angeles is spread out, and its streets are long, creating the illusion of movement.
On the other hand, like the U.S.'s progress with racism in general, sometimes it feels like we're not really going anywhere.