Railway track

[sandmaster]

Lengths of track used to be joined together using fish plates - and a gap was left between adjoining track to allow for expansion. This resulted in the comforting rhythmic noise now missing from railway journeys. How have the engineers overcome the problem of expansion and allowed the laying of track end to end without gaps?

[ChuckFickens]

it's welded so effectively becomes on long bit of track so expands uniformly along the whole length of the track.

The gaps used to be left to allow each little bit of track to expand without forcing itself up against the neighboring bits and buckling, there are no neighboring bits now.

[dundurn]

http://en.wikipedia.org/wiki/Welded_rail#Conti nuous_welded_rail

The problems haven't been entirely overcome. There were three derailments in the late 60's that caused a lot of heart-searching at the time and some modifications. Examination of the track on a regular basis is still required.

[sandmaster]

I can understand the theory Chuck, but in practice I think it's a bit iffy, as Dundurn intimates. I just miss the old diddley dum noise!!

[Cathyhuns]

The track is also stressed, ie stretched, so that as it expands with the temperature it still remains under tension. The level of stressing is changed as the ambient and expected temperature changes.

On the London Underground the PPPs, ie Metronet and Tubelines, are supposed to keep an eye on the weather and set the correct tension while the system is closed overnight. Some of the problems the Tube system has when it gets hot or cold have been when the PPPs haven't done this pre-tensioning properly and the track can't react correctly to the weather.

[sandmaster]

Thanks for that answer, Cathyhuns. It explians a lot. It muts be complicated monitoring and adjusting stress levels and I would really like to know how they do that, but I don't think this forum would have the space for the answer!!