As someone then living in Studio City but working in Santa Monica, we all knew how to use the residential streets to get around blockages of the 405. Mulholland (which is very much residential) to Laurel Canyon, for example. We told each other about them. I personally knew five or six alternates.
This may be spreading the word among people who don't try things on their own, but it's been a problem for the residents for many years. They do all sorts of things, from speed bumps to parking their cars in the narrowest (legal) places possible to slow down traffic. We would still use these routes.