Can anyone solve a conundrum please - what is this?

[cw]

Whilst commuting between Northampton and London, a colleague and I have noticed that there are many small white plaques beside the track. They can be located on the wall that separates track from platform, but equally they can be mounted at the base of metalwork such as lighting gantries or overhead power pylons.

Each plaque has a slider or lever in the middle of it, and they can be various colours such as red, blue or green. There seems to be a scale alongside the slider which can be in the up or down position, or sometimes mid-way.

One of these plaques can be seen in the following photo in front of the train: Southern_377_at_Hemel_Hempstead.JPG

There are also a couple visible next to the nearest track in this photo: 390043_at_Crewe_railway_station.jpg

We have been trying to work out what these plaques are, what the sliders do or indicate etc but all efforts to date have either drawn a blank. We would be very grateful if anyone here can explain and put us out of our misery!

Thanks in advance

Craig

 

[Darandio]

I have often wondered as well. My first guess would be something to do with distance between platform and nearest rail or maybe cant?

 

[Nym]

It's somthing to do with electrified lines, states the distance to nearest rail, cant etc. but don't know more detail than this...

 

[ainsworth74]

Not just electrified lines they appear I've seen them on plenty of un-electrified lines. I would also quite like to know what they mean, its been bugging me for ages as well!

 

[Striker]

I'm not a rail expert or rail enthusiast in the slightest, but I would guess they are gauges to indicate the height of the nearest rail.

 

[DaveNewcastle]

Yes, they indicate the intended height of the railhead, which is necessary information in track maintenance.

It was discussed informatively in this thread a year or so ago, which might be helpful.

 

[Striker]

Yes, they indicate the intended height of the railhead, which is necessary information in track maintenance.

It was discussed informatively in this thread a year or so ago, which might be helpful.

I was correct then.

 

[Inverness_App]

You are all correct. These are called datum plates. The red block on them indicates the height of the rail. The plates also have details of what the cant is and the distance from the plate to the running edge of the closest rail. They are commonly found on platforms but are also on bridges sign posts signals etc. They are used to monitor track movement and to help with maintenance. Hope this helps you.

 

[Hydro]

Red indicate the track can be moved to a new design if needed, green indicate the track must maintain a set design and any remedial work must be to that design. Basically once a green block plate is set, the track has to be moved back to the measurements
on the plate. On a red block plate, the block and plate indications can be changed to whatever state the tracks in. Green blocks are for where strict clearances have to be maintained.

 

[cw]

That's great, thanks for your help everyone!

Craig