Holy Cow! This is what is worrying me about everybody screaming for everyone to get out right now. I personally feel the people in Houston should stay until tomorrow to let the people in the southern counties out. Houston is huge and densely populated. It takes an hour and a half (from Nasa Rd 1 to Conroe) to cross it during non-traffic times. I suspect that is why the government is asking Houstonians to stay put for now.
In Tampa Bay, we stagger evacuations...Pinellas evacuates first, so they can get across the bridges and out of Tampa, the Tampa, and finally folks in Manatee.
Worked well last time we evacuated.