That's what a hurricane evacuation looks like in Houston and elsewhere.

Houston is actually well inland from the coast, far from any storm surge (flooding is a major problem, but it's not storm-surge related). When the coastal residents evacuate it's a large number of people trying to go through Houston.

The horde doesn't want to stop because they can see the crowd around them and know there will no vacancies. The locals should probably just stay off of the roads passing through and the evacuees will be like a swarm of locust that suck gas stations dry, but no worse.

New Orleans / Katrina is a good case study. Almost everyone evacuated along two roads. I've never seen an after-report on this: where did these self-evacuees go, were they given any directions, any evacuation destinations by the authorities?