Ok, I am an engineer...

(Disclaimer: I work for a transportation agency in another state and am very familiar with the National Bridge Inspection Standards. I am giving my personal opinions and observations and not stating any official position or anything else but my opinions. Now, back to the discussion.)

So here goes...

1. Looks ARE deceiving, especially from the distances we are seeing things. The only way to really tell is "up close and personal".

2. The main cross channel span was over 460 feet. The "domino pattern" (progressive collapse) as seen in the video is caused by the span failing at one end and pulling the rest of the span down.

a) The approach spans might have collapsed due the the shifting of the main span as it failed (on the side it failed).

b) I am not familiar with the area, except what I have seen on the news, but I would expect that the railroad and the roads on either side of the river would be back in operation by late next week. The river channel will probably take a couple of weeks to clear once the NTSB has finished their high-resolution surveys.

c) No argument here. I was not pleased that it seemed that even before the dust had settled, Homeland Security had declared that the collapse was not terrorist related. The eyewitness reports that I have heard (again from the media) tend to support that conclusion, but I would appreciate a more measured approach.

3) That a train was passing under the bridge at the time is, initially to me, just as coincidental as there only being 50 vehicles on the bridge (4 lanes being closed). Also, the photos I have seen show no damage to the piers (piling), so I would look elsewhere for the cause of the collapse such as the truss ends that were atop the pier.

a) Yes, and apparently the train was pulling empty cars, as no HazMat situation was noted.

b) The vibrations from an unloaded train are much less that those of a loaded train (F=Ma). Additionally, the speed of the train also is a factor, faster trains produce stronger vibrations than slower ones. A long, loaded, fast moving train would cause considerable vibration than a slow unloaded one, and could theoretically, add to fatigue inducing stresses.

4) I wouldn't initially think so - I would tend to see it more as coincidence. Prudence dictates though, that every possibility
be throughly investigated.

5) I have a BS in Mechanical Engineering. I am not a licensed Professional Engineer.

6) You got it.