hi there i'm new and a station platform query (datum plate)

[truckman060473]

hi i am new and my first question is about the wall on the platform between where you step on a train and the rails themselves. what are those plates built into the wall about 6 inch square that have a knob that looks like it can slide up and down a bit like a volume control on a studio mixing desk?

 

[DaveNewcastle]

hi i am new and my first question is about the wall on the platform between where you step on a train and the rails themselves. what are those plates built into the wall about 6 inch square that have a knob that looks like it can slide up and down a bit like a volume control on a studio mixing desk?

Hi! Yes, they control the volume of the engine's noise when its in a station and you're trying to understand a platform announcement!

No, I'm kidding. Seriously, they mark the designed height of the railhead. This needs to be measured and recorded somehow, because the track, ballast and any underlying formation may move with time (largely due to the weight of traffic but also natural compression) and during tamping of the ballast.
Those gauges are a means of noting the height which can then be used to calibrate the track when its being monitored and maintained to determine by how much it must be raised (or lowered) to remain within its designed height.

 

[SWT Driver]

Old Timer will give you an exact name & detail about them.

 

[90019]

I was about to ask about what those were because I've noticed them more recently and have been wondering

 

[Old Timer]

As has already been mentioned, they record details of the track position and geometry so that the Maintainer can ensure that the relevant track position is maintained.

They are called Datum Markers and should be provided at each lineside structure.

 

[yorksrob]

Excellent question, I've always wondered what they are but had never thought to ask!

 

[Old Timer]

Well there are a number of professional infrastructure engineers who are now about here, so do feel free to ask anything Infrastructure related and we will seek to answer your query.

No question too simple or too complicated.

 

[Jon10]

What is the rough comparative cost of sleepered rails and concrete slab track?

Why would have, for instance, much of the "East London Line" Overground rebuild been done in the latter? Presumably the concrete will last for, say, 60 years, so very long term, is it cheaper?

 

[chappers]

What is the rough comparative cost of sleepered rails and concrete slab track?

Why would have, for instance, much of the "East London Line" Overground rebuild been done in the latter? Presumably the concrete will last for, say, 60 years, so very long term, is it cheaper?

As slab track is rarely installed I don't know the cost per yard comparison. As you allude to, slab track is more expensive to install but the cost saving is made on the comparative lack of maintenance requirement compared to standard track. There is no formation failure and a much reduced risk of rail breaks. I wouldn't be aware if any as been installed long enough to determine how much longer it lasts prior to renewal.

 

[Skie]

The Loop line on Merseyrail was built in the 70's and has just had the final section of track bed renewal done to it recently (after 5 years or so of work in stages). 30ish years, but those tunnels have a lot of water ingress and are heavily used. I'd expect it would last longer in less hostile environments.

 

[Old Timer]

What is the rough comparative cost of sleepered rails and concrete slab track?

Why would have, for instance, much of the "East London Line" Overground rebuild been done in the latter? Presumably the concrete will last for, say, 60 years, so very long term, is it cheaper?

The ELL was done in concrete as a noise reduction scheme.

Yd for Yd it is considerably more expensive than conventional track, and brings with it the need for special sub-grade treatment, as well as drainage.

Once down it should last indefinitely.

The section of the Fast lines at Carlton Road Jct and Mortimer St tunnel was installed during 1978, and is still going strong, and represents the first mainline use in the UK. There were a variety of problems at this location including both clearances, as well as stability, issues with the retaining walls in the cuttings.

A test section on open line has been laid on the Manchester Lines just to the north of Crewe within the last few years.

Concrete track is preferred where there is a particularly tight clearance problem, as the track is installed in a permanently fixed position which means that the clearances can be reduced against what is possible on fully ballasted track.

 

[DaveNewcastle]

. . . . Concrete track is preferred where there is a particularly tight clearance problem, as the track is installed in a permanently fixed position which means that the clearances can be reduced against what is possible on fully ballasted track.

Ah! I didn't know that! Tho' it makes complete sense, in principle.

But when I consider the implications for dynamic loads on ridgid formations, then I don't know which aspects of the received wisdom on dynamic clearances (arising from vertical variations within design tolerances of ballasted track) can be eliminated when designing rigid concrete structures.
So could you elaborate, please, OT? What variations of a vehicle's envelope can be disregarded when the minor track movements on ballast are eliminated?
(I'm particulary interested in curves and tunnels) Thanks.

 

[Jon10]

Ballasted track - v - slab track:

Is there a different amount of wear on the rolling stock and the rails?

Presumably slab track has a lot less "give", so does it make the track wear out quicker, or destroy train suspension systems quicker?