Something i've always wanted to know

[callum112233]

Since I was young, I have always wondered something.
On platforms at railway stations, near to track level, there are various small white plates screwed to the side of the platform with a red kind of knob on them.
If anyone knows what im on about, it would be nice to finally know what the purpose of these things are
Thanks.

 

[ole man]

Since I was young, I have always wondered something.
On platforms at railway stations, near to track level, there are various small white plates screwed to the side of the platform with a red kind of knob on them.
If anyone knows what im on about, it would be nice to finally know what the purpose of these things are
Thanks.

There are datum plates, that tell you what level the track should be.
They are also found on OHLE structures telling you how far the track should be away.

 

[callum112233]

yes, one of these. Something I've always pondered
Thanks.

 

[142094]

Couple of topics recently with a bit more info, have a search for them.

 

[ralphchadkirk]

The topic explaining this really should be stickied.

Someone like Hydro may well come along in a minute and explain the intricacies of the datum plates, but basically they tell you the position of the track in the relation to the structure on which the plate is located.

From that plate you can tell it is the down line. The track should be 2915mm from the plate, and the superelevation should be 35mm. I think the fact it is the red knob means that the track should be maintained to design specs.

 

[callum112233]

and the superelevation should be 35mm.

And this means the angle that the track 'tilts' to the left or right?

 

[ralphchadkirk]

And this means the angle that the track 'tilts' to the left or right?

35mm is the difference in height between the inner rail and the outer rail. Usually the lower rail is on the inner of the curve, but I believe adverse cant can occur.

 

[Barrett M95]

35mm is the difference in height between the inner rail and the outer rail. Usually the lower rail is on the inner of the curve, but I believe adverse cant can occur.

Carstairs Junction. The spur to/from Edinburgh where it joins the WCML has adverse cant. One of the reasons for the 15mph (?) restriction.

 

[Railsigns]

yes, one of these. Something I've always pondered
Thanks.

That's a copyrighted photograph that you've pinched from my website without my permission:

http://www.railsigns.co.uk/info/other1/other1.html

 

[callum112233]

oops, wasnt sure it was copyrighted, i'll take it down.

 

[ralphchadkirk]

If it's not taken by you, and isn't under a copyright licence which allows you to use it, then it's a good idea not to post it.

 

[Hydro]

Carstairs Junction. The spur to/from Edinburgh where it joins the WCML has adverse cant. One of the reasons for the 15mph (?) restriction.

I ran the Track Recording Unit over that last week, the trace looks all wrong! But of course, it's the geometry design...Makes you feel a little weird tilting to the wrong side too.

The datum plate, a breakdown:

CP No. = Core Point number. A Core Point is just a point at which you take measurement. This is No. 58. A platform will have one every 10m.

Offset: How far to the running edge (inside edge) of the nearest running rail.

DN: Nearest line is the Down. Can read UP, DM, UM, DF, DM, US, DS etc....

Cant: How much cant is applied at that point

Design Level of Nearest Rail: The top of the red slider is set to the height of the nearest running rail. If this cannot be done, and, if there's no place to affix the plate to get the slider at the right height, you can put at offset on it. In this case, the slider is in fact 300mm higher than the nearest running rail. I've had to do this a few times when a conductor rail obscures the self levelling laser pointer that is used for this (sticks on top of the railhead), so stuck the plate on and used a tape measure from top of juice rail, and added the nominal height from railhead to top of conductor rail. Rough and ready, but then again, so is track engineering sometimes.

 

[DarloRich]

Hydro - thanks!

That Carstairs curve just feels WRONG! first time i went round there i thought the train had broken! (i was quite young!)

 

[Barrett M95]

http://www.youtube.com/watch?v=Otg8RlLIXEM

You can sort of see when the first train crosses the junction it looks somewhat awkward as it leans the "wrong" way.

 

[90019]

I ran the Track Recording Unit over that last week, the trace looks all wrong! But of course, it's the geometry design...Makes you feel a little weird tilting to the wrong side too.

Do you know what the reasons are for the adverse cant there?

 

[Barrett M95]

The main curve (for the WCML) is (as you are travelling south) to the west. The ECML route is a junction to the east. The junction actually diverges in the middle of the curve which is canted to allow for trains at 110mph. Therefore if you are a train heading south you are canted over to the right but are then routed to the left.

Does that make sense?

 

[Welshman]

Makes perfect sense to me.

Could they not move the diverting junction back to the Glasgow end of Carstairs station, so that the line to Carlisle could be as now and the line to Edinburgh be canted for a left turn?

 

[exile]

If it's not taken by you, and isn't under a copyright licence which allows you to use it, then it's a good idea not to post it.

For goodness' sake, 90% of the images posted on the net were originally posted somewhere else. Don't post images if you don't want people to copy them - or put a big warning notice on the page at least.

 

[causton]

For goodness' sake, 90% of the images posted on the net were originally posted somewhere else. Don't post images if you don't want people to copy them - or put a big warning notice on the page at least.

+1. If you want people to not post your images on forums, I would advise you (think again! or) put a warning that you don't want people to do that. I thought the addition of a picture was helpful, and not intending to defraud your efforts! A tiny (c) notice on the front page should be placed in a more prominent position on each page if you're going to take that stance IMO!

 

[Crossover]

I'd say generally speaking, saying where you got the image from would be good courtesey and would *probably* keep the authors happy.

Anyway, as for datum plates, it has appeared a few times and I believe there is another colour other than red (is it green?) where the rail doesn't have to be kept at that level and the slider can be adjusted as the track "beds in"

Thus, I believe (from the many things I have read on the forums mainly) that you would usually find the red ones where there is a clearance problem if the track were to move (e.g. platforms, bridges, catenary supports or other rail infrastructure

 

[callum112233]

Do these datums get checked regular to make sure the posistion of the track falls within the specified standard? It would be time consuming checking them all by hand wouldn't it?

Again, sorry about the picture, I should have stated where I got the picture from.

 

[Hydro]

Anyway, as for datum plates, it has appeared a few times and I believe there is another colour other than red (is it green?) where the rail doesn't have to be kept at that level and the slider can be adjusted as the track "beds in"

Thus, I believe (from the many things I have read on the forums mainly) that you would usually find the red ones where there is a clearance problem if the track were to move (e.g. platforms, bridges, catenary supports or other rail infrastructure

It's the other way around. The red ones can be moved to the position of the track. The greens have to have the track re-positioned to them. As track gets relaid through platforms, it's more common to see green ones to maintain the clearances.

Do these datums get checked regular to make sure the posistion of the track falls within the specified standard? It would be time consuming checking them all by hand wouldn't it?

Yes, they are, and it is. A structure register is kept at a local level, and all of these must have datum plates if they fall within a certain distance of the track. I was involved in a programme to fit these plates to all the structures on the patch I worked on. If the structures already had plates on, then you measured them to check the details on the plate, and update if necessary.

Platforms are a bit different, as the plates aren't actually strictly related to a platform survey - which involves more measurements, such as offset from running rail to platform edge, height from rail to top of platform, curve radius and applied cant.

 

[callum112233]

Sorry to bring up an old thread but I just watched this video and remembered talk of adverse cant at Carstairs.

http://www.youtube.com/watch?v=jZS_UKtFAMM&feature=related

Why was the line built like that? why wasn't it built so that the cant was normal?

 

[Hydro]

Sorry to bring up an old thread but I just watched this video and remembered talk of adverse cant at Carstairs.

http://www.youtube.com/watch?v=jZS_UKtFAMM&feature=related

Why was the line built like that? why wasn't it built so that the cant was normal?

Because the curve has to join the WCML, which curves the opposite way and thus has cant applied to the opposite rail. You can't just switch rails instantly, you need a transition otherwise you get a dangerous twist

 

[Welshman]

Barrett M95 and Hydro have given the answer.
But would there be space to implement my previous suggestion in post 17?