Quote Originally Posted by Red Harvest
Evacuation was ordered by Nagin on the afternoon of the 27th in New Orleans. It was made mandatory at 9 AM on the 28th -- the BBC appears to have confused the two and ignored the initial evacuation calls.
According to CNN, Nagin advised evacuation on Saturday 27 and made it mandatory at 10 am on Sunday. Blanco and Barbour had already declared emergency status on Friday 26 around 4 pm.

As for evacuation times, the rule of thumb in emergency situations in modern cities is 4 times the normal time needed to leave a city, provided of course that exit roads are not blocked (one-way outbound traffic must be guaranteed by traffic control) and public transport is available for those without cars. Assuming the normal time to be an average of 2 hours, that makes 8 hours. Plus 4 for packing and other eventualitiesm that makes twelve. However, you are probably right that the metropolitan area is particularly difficult to evacuate. In the Louisiana Hurricane Evacuation Plan it says:

  • The Greater New Orleans Metropolitan Area represents a difficult
    evacuation problem due to the large population and it’s unique layout.
  • This area is located in a floodplain much of which lies below sea level
    and is surrounded by an extensive marine estuarine system of lakes,
    canals, bayous, the Gulf of Mexico and the Mississippi River. Some
    parish storm drainage systems discharge into area waterways. High
    water levels would impede adequate pumping and prevent relief against
    flooding from heavy rainfall.
  • It will take a long time to evacuate large numbers of people from the
    Region.
  • The road systems used for evacuations are limited, and many of the
    roadways are near bodies of water and susceptible to flooding.

Mind you, three-quarter of residents of the wider area did get out in time. There were traffic jams, as there always are, but they were resolved as they always are. Bo broken bridges, no flooded roads. Most people drove out along the assigned E-roads by private means as the Plan states in its list of 'Assumptions':

  • The primary means of hurricane evacuation will be personal vehicles.
    School and municipal buses, government-owned vehicles and vehicles
    provided by volunteer agencies may be used to provide transportation
    for individuals who lack transportation and require assistance in
    evacuating.

Those left behind were in many cases literally left behind. There were no buses. In the Plan's paragraph on 'Recommended Evacuation' (the stage preceding mandatory evacuation) one of the first items mentioned is this:

  • Mobilize parish/local transportation to assist persons who
    lack transportation or who have mobility problems.

I keep wondering where those buses were. Maybe you are right and it is just because I am a European. But they were part of the plan...