By the time your life is in imminent peril it is too late.
I was in Houston during Alicia. I was lucky to live in a second story apartment because the first floor units were all flooded. I wish I had evacuated, but by the time I decided I needed to get out it was too late to go anywhere. I was stuck there for days.
I helped some friends pack up and evacuate from Bolivar Peninsula several days before Ike hit. Fortunately they did not wait until their lives were in imminent peril because if we had they would now be dead. There was no trace of either of their houses after the storm.
I have also lived through several flash floods during my lifetime (one of the joys of living on the Brazos and Colorado Rivers). Again, if you wait until your life is in imminent peril it is too late to evacuate.
Then feel free to evacuate, but see my post #59 above, illustrating that evacuation is not a risk-free decision and comes with its own costs and dangers. For the record, I evacuated the day before Katrina, but otherwise have remained in place all my life, for more direct hits and near misses than I can remember.
One of these days a storm is going to take an unexpected swerve and catch hundreds of thousands of compliant goobers out on the roads.