What Does Code Yellow Mean?

I have one question about the federal response (or lack thereof) to Katrina that I think needs exploring in a big way. Just what does the Department of Homeland Security's color-coded alert system really mean? Given the lack of response and preparedness to Katrina, just what protection did this Code Level alert give us?

Here is the defintion of Code Yellow from the Department itself:

Elevated Condition (Yellow). An Elevated Condition is declared when there is a significant risk of terrorist attacks. In addition to the Protective Measures taken in the previous Threat Conditions, Federal departments and agencies should consider the following general measures in addition to the Protective Measures that they will develop and implement:
Increasing surveillance of critical locations;
Coordinating emergency plans as appropriate with nearby jurisdictions;
Assessing whether the precise characteristics of the threat require the further refinement of preplanned Protective Measures; and
Implementing, as appropriate, contingency and emergency response plans.

So, under this elevated condition yellow, the federal government was supposed to have coordinated "emergency plans as appropriate with nearby jurisdictions," and implemented, "as appropriate, contingency and emergency response plans."

I know this was not a terrorist attack, but still, wouldn't you think our level of preparedness for something big would have been much better?

Can we presume that had this been a terrorist attack in New Orleans, it all would have been responded to much more quickly and effectively? Can we presume that if the levees had been blown up by terrorists on a sunny day in New Orleans that the federal response would have been swift and massive? We would all hope so. And we would wish it so, in part, because our government has set up this color coding response system to terrorist attacks and told us that there are good reasons for it. I mean, some deep thinking went into this, didn't it?

Here is a summary of the failures by government before and after Katrina from the BBC. I suspect that any final report from any commission is going to come to most of the same conclusions as this piece of journalism does just nine days after the event.

Finally, the photo of all those buses sitting in water is pretty disturbing when you think about all the people in New Orleans who had no way to get out but would like to have gotten out. Why is it that local and state officials could not have found a way to have mobilized these buses to have gotten more people out on Saturday and Sunday before Katrina struck?