This humble blogger almost melted in his sleep a few weeks ago, and the idea that 1.1 million people can evacuate from a refinery explosion at 4am is ridiculous. Large scale evacuations might be possible when you have advanced warning of something, like a hurricane (though not all people have the resources to do so), but at 4AM the acid cloud is just gonna eat us and 400,000ish cars couldn't possibly get out of Philly quickly enough.
...adding that banning cars and have everybody take literally any other alternative means (walk, bike, mobilized bus fleet) is the only possible way a sudden mass evacuation could avoid just being a parking lot but lol not the plan.