Transition vs cant question

[kettle8632]

Hi all,

Another question I hope someone might be able to answer.

Is there any situations where you would start increasing the cant before the actual curve starts. For example 0mm- 20mm cant in the straight before the curve and then the cant would continue to rise to the TE.

Where I am they want 80mm cant on 100m radius curves (max speed 22 mph), but the curve is so short they can't get it up to 80mm quick enough, so they are planning to extend the rate of the cant in to the straight.

To me it doesn't sit right having cant on straight track, but I maybe wrong.

Thank in advance.

 

[Joseph_Locke]

Hi all,

Another question I hope someone might be able to answer.

Is there any situations where you would start increasing the cant before the actual curve starts. For example 0mm- 20mm cant in the straight before the curve and then the cant would continue to rise to the TE.

Where I am they want 80mm cant on 100m radius curves (max speed 22 mph), but the curve is so short they can't get it up to 80mm quick enough, so they are planning to extend the rate of the cant in to the straight.

To me it doesn't sit right having cant on straight track, but I maybe wrong.

Thank in advance.

The other way round (longer geometry transition, short cant transition) is "relatively" common, but I've never needed to go the other way. My question would be "why 80mm on a very short 100m radius curve"? UK practice is shortly to change so that, on tight curves, we use the cant deficiency up first, then apply the cant. On your curve why not 110mm deficiency and 40 cant? or even 75/75mm?

That said, there is nothing inherently wrong with a canted straight, but watch out for the changes in rates of gain and the maintainer lifting it off later by accident!

 

[Ploughman]

Are you on standard gauge or narrow?
22mph would not be a normal published speed.
It should be rounded down to the nearest 5mph multiple below in this case 20 mph
Unless that is you are working in KMH even then it should be to the nearest 5 below.

 

[Trog]

A 1/4" or so of cant on the straight was standard practice on some railways, in the dim and distant past. As they thought that it would help stop the wheels from hunting.

 

[kettle8632]

Are you on standard gauge or narrow?
22mph would not be a normal published speed.
It should be rounded down to the nearest 5mph multiple below in this case 20 mph
Unless that is you are working in KMH even then it should be to the nearest 5 below.

I'm in Australia, so the track speed is actually 35kph, and we are on narrow gauge 1067mm.

 

[Joseph_Locke]

I'm in Australia, so the track speed is actually 35kph, and we are on narrow gauge 1067mm.

I'm even more curious now, as I get E+D to only be 109.4mm, so why so much cant? Surely 60 cant 50 deficient (equilibrium at 25kph) would be better, gives you a cant gradient about 24m long?

 

[L&Y Robert]

Hi all,
To me it doesn't sit right having cant on straight track, but I maybe wrong.

Thank in advance.

My pre-war Honby "O" guage tinplate streight track sections are ALL canted in anticipation of a curve to come!
I was always irritated by this as a child!

 

[miikey]

Hmm,

To maximise the Rate of Gain of Cant/Deficiency you have to have E=D throughout the curve. This will give you the shortest Transition Length, assuming you are using your max RgE and RgD at 55mm/s. (RgE and RgD = Rate of Gain of Cant/Deficiency).

There is not much reason to have the track canted before a curve, that is what the transition is for. As long as your RgE and RgD do not exceed 55mm/s throughout your Transition and your Cant Gradient is not over 1/400, you should be fine.

Either you design your curve with a pre set length of your transition (what most curve realignment design is) or you can make your ideal Transition length. This is usually when you have a full renewal.

I hate Hallade.