As the app's announcement post said "The goal of the feature is to reduce the amount of these intersections, not completely eliminate them." While the feature is only available in Los Angeles for now, it will soon roll out in New Orleans and will eventually be available around the world. Take note that if you're in LA, Waze automatically switched on for you. In case it's not working out, you can always switch it off under Settings.
This article by Mariella Moon originally ran on Engadget, the definitive guide to this connected life.