Having multiple routes of egress is key. If you're preparedness minded its easy enough to watch traffic patterns around a holiday weekend and extrapolate that for a mass evacuation.

What main freeways were crowded going out of town last weekend for the holiday weekend? Those would certainly be areas to avoid. Also getting a Thomas Brothers guide or Google Maps and pre-plan alternate routes around those congestion areas.

One of my evac plans calls for dirt road that cuts through a national park that puts me scores of miles out of town before hitting the highway system. Its one of many plans I have for getting out.

Especially if your plan is just to get out of a danger zone, consider going in the opposite direction and then figuring a way to loop around. It may add a couple hundred miles but better than being stuck on the side of the road with 60,000 other people.