As someone that grew up in Yorba Linda (or, "Yuppie Linda" as we called it in high school), I can understand the road clogging. Essentiall YL is built upon a hill. YL Blvd is the "upper" main highway, and Orangethorpe/Esperanza is the "lower" main road. They run East/west. All the residential streets run up or down hill (that'd be north or south) off these 2 thoroughfaires. Truth be told, they're both only 2 lanes on either side. So it's very easy to see how the residential road would clog quickly, and the main highways even quicker. To make matters worse, YL Blvd is divided with concrete islands. It's also the road closer to the hill crests, that were burning.

Seems that reverse 911 could have helped if it'd be set quicker. But it also just might be poor planning in setting up the city for an evacuation.

I'll see if I can set up some pics from my parents and friends later.