When hurricane katrina struck new orleans in 2005 why was it harder for black residents than white residents to get out of the city?

Its a question still unanswered today surveys and studies showed that nearly all those that were left behind with African Americans which portrayed the race act but other studies showed that those that left were families that were financially stable and could afford to move to a safe flood protected areas and had additional resources to evacuate more easier than others.

Alot of speculation but nonetheless