>I'm not too clued up when it comes to track maintenance - can someone care
>to enlighten us as to what "tamping" and "laser aligning" does? Is it
>something to do with packing down the ballast material to make the rails sit
>better? (or should I say "sleep" better? ;) )
Pretty much sums it up actually, you 'tamp' the ballast under the
sleepers to align the rails.
The automatic tamping machines use a varity of methods to determine
the correct alignment , ranging from operator skill, to laser
reflected off a dolly pushed out in front of the machine itself and
computer records of the 'design' track alignment.
The NSWRTM has a TDX tamping machine, that when it automatic mode,
pushes a dolly 10 metres or so ahead of itself, which has a steel wire
threaded through it and back to the 'back' end of the machine proper.
When the tamping head is lifting, there are two little 'vanes' on top
of the tamping head, that rise and hit the wire as the sleeper lifts.
This completes an electrical circuit and stops the lift. All the operator
then does is align the head around the next sleeper, the machine itself
tamps the dips out.
Track structure and alignment is an entire area of engineering in it self.