I have seen these machines in action in Britain, with the WCML being redone, the gravel trains are massive and very long, along with the rail and sleeper wagons...
I have to say the video was fasinating to watch, but when I saw them in real life, blimey they are noisy, and you can feel the shudder under the ground when the gravel is being placed under the track.
The only thing I did notice, they never worked on over bridges with these machines, as the train weighed too much, that it could put pressure on the bridge, that it could force the under bridge to collapse. So they would race the train over to the other side of the bridge and start again, track laying.
Brilliant video, who-ever filmed it, must have been there for ages watching the track laying process.
Joe Airtime