In Phoenix, major streets are on about a 1 mile grid. The major streets (mostly) go through and take you wherever you want, they're very fast and optimized for heavier traffic.

The rest of the streets connect to people's homes, they're full of speed bumps and such and while some do go through, it's a slow and twisty road with no certainty unless you know that street (or peer at the GPS) so you'd never take those roads unless you actually wanted to go into that community.

I find that it strikes a pretty good balance between helping people get where they're going and making sure that people don't have tons of cars zooming right past the front door.