I detect a little re-writing of history here.
Correct me if I'm wrong, but the initial offer of an Amtrak train was made on Wednesday, August 31 (as reported by the Jackson MS Clarion-Ledger and linked on OTOL). But, unlike what is now being reported, there was no train or route available on 8/31 and certainly no way to run two trains a day starting that day as is now being implied. According to the original article, on 8/31 routing logistics were still being arranged and the train was not yet available. According to BNSF press releases, their line into Avondale Yard in New Orleans was not inspected, repaired and reopened until late Thursday, September 1.
Bill, on the above points you would appear to be correct. Amtrak only offered on Wednesday, they were not in a position to actually start on Wednesday. However, the country didn't start really learning of the problems at the Dome and especially the Convention Center (CC) until Thursday and Friday, with evacuations still on going on Sunday the 4th.
Given that daylight operation was almost mandatory, Amtrak had no route into New Orleans until Friday morning, 9/2. Add to that the fact that Amtrak did not have even one train positioned until Friday, 9/2. The fact is the trains were made available at as early a date as Amtrak could ready them and that day was Friday, 9/2, not Wednesday 8/31. So at best, the earliest Amtrak could have run one evacuation train was Friday and by then it was already too little and too late.
Actually daylight was not mandatory. The first run into NOL was originally scheduled to depart towards NOL on 9/2 at 7:00 pm, with a departure time of Midnight. That run however got cancelled, by FEMA to my knowledge, because they had no buses to get people over to the train.
As I noted above though, trains could have and should have run all day on Friday and Saturday, as they were still moving large numbers of people into Sunday morning.
By that time two other actions had made the Amtrak offer moot. One: Texas had already taken as many evacuees as they could handle (and the only practical destination for Amtrak evacuees was Texas). Second: Armstrong Airport had both runways, ATC, and IFR operational and evacuation by air to any US destination was now possible, practical, and far more effective that putting them on a train for a 130 mile ride to busses that had nowhere to go.
As noted in the same article that I had linked to originally, FEMA also screwed up the evacuation from the airport. So this option wasn't as viable as it might seem. I quote from the article:
Anger was also rising at federal officials, who often seemed to be getting in the way. At Louis Armstrong International Airport, commercial airlines had been flying in supplies and taking out evacuees since Monday. But on Thursday, after FEMA took over the evacuation, aviation director Roy A. Williams complained that "we are packed with evacuees and the planes are not being loaded and there are gaps of two or three hours when no planes are arriving." Eventually, he started fielding "calls from various airlines saying, 'Well, we are being told by FEMA that you don't need any planes.' And of course we need planes. I had thousands of people on the concourses."
Additionally getting people from the Dome and the CC to the airport was much harder than it would have been to reach Amtrak. In fact, to my knowledge, very few of those trapped at the dome or the CC left via the airport. Most people from those two places, rode buses the whole way to where ever they ended up.
I really do not think the Amtrak plan was practical, particularly by the time it was available. Witness that the one evacuation train, operated 9/3 (one day after the train was actually available) train took a grand total of 97 evacuees: less than single 737 and barely more than two busses. The reason Amtrak was not used may just be because, by the time Amtrak was a real option, it was not all that useful.
As I posted elsewhere in response to a similar statement by you I believe, the train left so empty, because of the ability of officials to control the buses needed to get people to the train. It was not a lack of people available that caused it to leave so empty.