Track Curve: How do you measure it?

[AlexM96]

Can anyone explain to me how to measure track curve and radius simply?

 

[zwk500]

If this is for work, you should have a standard to follow.
If this is for a course, your tutor should have the information.
If this is for interest, on Google Earth you can draw circles and you have to eyeball it over the track, allowing for the transition curves.

 

[DoubleO]

Can anyone explain to me how to measure track curve and radius simply?

Do you mean from a map, from a drawing or actually on the ground?

 

[DelW]

Can anyone explain to me how to measure track curve and radius simply?

This short thread might help:

How to measure Curve radius?

Hi, does anyone know and could tell me how to measure curve radius? I would like to compare the sharpness of curves (Rutherglen, Earlestown, Shipley, St Pancras LL) for example to see which one is the sharpest. Thank you!

www.railforums.co.uk

 

[AlexM96]

This short thread might help:

How to measure Curve radius?

Hi, does anyone know and could tell me how to measure curve radius? I would like to compare the sharpness of curves (Rutherglen, Earlestown, Shipley, St Pancras LL) for example to see which one is the sharpest. Thank you!

www.railforums.co.uk

Cheers

 

[alf]

I would like to be able to measure curves radius.

I often travel over the 25 mph (uncanted) rail curve on the London side of Southampton station & fantasise about how, using railway land on either side, they might be raised to 40 mph..probably saving a minute each for 8 passengers trains an hour.
That is 800 passenger minutes saved an hour, 14,000 passenger minutes saved a day. 70,000 passenger hours saved a year.

I reckon(from sight) the curvature is no tighter then the 45mph(canted) curve on the four tracks between Clapham Junction & Battersea Park which you see from the Southampton train after Clapham Junction.
I want to compute if I am talking rubbish by measuring these curves on a map.
But exactly how, with just a ruler?

 

[zwk500]

I would like to be able to measure curves radius.

I often travel over the 25 mph (uncanted) rail curve on the London side of Southampton station & fantasise about how, using railway land on either side, they might be raised to 40 mph..probably saving a minute each for 8 passengers trains an hour.
That is 800 passenger minutes saved an hour, 14,000 passenger minutes saved a day. 70,000 passenger hours saved a year.

How'd you save 1 minute by raising 25mph to 40mph for less than half a mile?

I reckon(from sight) the curvature is no tighter then the 45mph(canted) curve on the four tracks between Clapham Junction & Battersea Park which you see from the Southampton train after Clapham Junction.
I want to compute if I am talking rubbish by measuring these curves on a map.
But exactly how, with just a ruler?

Easiest way is to download Google Earth for free and use the circle tool to measure the radius.

 

[Ken H]

When they got mk3's on west coast there was a project to speed things up a little. Cl87 could do 110. Mk3 could do 125. They tweaked the brakes to allow harder braking. Passengers felt more force when braking but was thought worthwhile.
But back to topic, they did work to see if they could go round curves faster.
They elevate the outside rail so the passenger feels less sideways force when cornering. The idea is the elevation or cant counteracts the sideways force so the passenger doesnt know they are cornering. But they thought 'what if we allow some lateral acceleration.' So they did that. The elevation lacking in the outside rail was known as cant deficiency.
The radius of the curve and desired speed sets the cant.

 

[swt_passenger]

How'd you save 1 minute by raising 25mph to 40mph for less than half a mile?

Easiest way is to download Google Earth for free and use the circle tool to measure the radius.

The Southampton tight curve is about a 200 yard radius, we had a thread about it before. It definitely isn’t railway land on both sides though, I don’t see how the radius can be increased without property demolition north and west of the line.

It’s not good quality property though. Probably not impossible to widen the rail corridor eventually, but highly unlikely in the present economic climate.

 

[Boodiggy]

Basic track survey is done using the hallade method. A google search will give you the basics but track alignment design is very complicated and lots goes in to it.

 

[zwk500]

The Southampton tight curve is about a 200 yard radius, we had a thread about it before. It definitely isn’t railway land on both sides though, I don’t see how the radius can be increased without property demolition north and west of the line.

It’s not good quality property though. Probably not impossible to widen the rail corridor eventually, but highly unlikely in the present economic climate.

Changing the curve isn't possible because of the pointwork at Northam Jn and the various bridges around it.

If you are to ever widen it to 4 tracks, you will have a hell of a time because the only feasible place for the 2nd western tunnel portal is on the north side, but that means you'll be taking out the Premier Inn, rebuilding the Kingsway Bridge and taking out Northam Rd (and all the houses adjacent to it, because you'd be removing the road access). It may not be prime central London property prices but it's still going to cost a monumental figure.

 

[Facing Back]

If the op is fantasising and having a bit of fun there is no need to let the economics get in the way of a theoretical exercise. Whilst travelling at less than walking pace on the ordsall chord in Manchester, I've often thought about the buildings I would knock down to provide a proper route between Piccadilly and Victoria. In fact the trip has often been so slow I would have had time to producing detailed engineering drawings.

It seems that everything on the railway costs a monumental figure.

 

[zwk500]

If the op is fantasising and having a bit of fun there is no need to let the economics get in the way of a theoretical exercise. Whilst travelling at less than walking pace on the ordsall chord in Manchester, I've often thought about the buildings I would knock down to provide a proper route between Piccadilly and Victoria. In fact the trip has often been so slow I would have had time to producing detailed engineering drawings.

Tbf the OP just asked how to measure it.

It seems that everything on the railway costs a monumental figure.

pretty much. Retrofitting is expensive.

 

[Irascible]

When they got mk3's on west coast there was a project to speed things up a little. Cl87 could do 110. Mk3 could do 125. They tweaked the brakes to allow harder braking. Passengers felt more force when braking but was thought worthwhile.
But back to topic, they did work to see if they could go round curves faster.
They elevate the outside rail so the passenger feels less sideways force when cornering. The idea is the elevation or cant counteracts the sideways force so the passenger doesnt know they are cornering. But they thought 'what if we allow some lateral acceleration.' So they did that. The elevation lacking in the outside rail was known as cant deficiency.
The radius of the curve and desired speed sets the cant.

Well, very slightly more complicated ( and quite some time since I looked at it ) -

* Maximum track cant is determined by what happens if you have to stop a train on it - last time I looked one rail could be up to 6" above the other, but that may date it if it's changed!
* Maximum cant deficiency is I think limited by passenger comfort - someone please correct me there - handily that is iirc measured in inches of cant, too.
* You have to go from flat to fully canted, and there's a limit to how fast you can do that which ( partly - the other part is the transition to the actual curve itself ) sets the minimum length of transition curves at a given line speed - so that is another geometry constraint.

The rules are all readily available at the RSSB, or at least were.

 

[Boodiggy]

Well, very slightly more complicated ( and quite some time since I looked at it ) -

* Maximum track cant is determined by what happens if you have to stop a train on it - last time I looked one rail could be up to 6" above the other, but that may date it if it's changed!
* Maximum cant deficiency is I think limited by passenger comfort - someone please correct me there - handily that is iirc measured in inches of cant, too.
* You have to go from flat to fully canted, and there's a limit to how fast you can do that which ( partly - the other part is the transition to the actual curve itself ) sets the minimum length of transition curves at a given line speed - so that is another geometry constraint.

The rules are all readily available at the RSSB, or at least were.

Correct - max cant 150mm / 6’’

Cant deficiency is much higher on the WCML where there is the Through Alignment Design for tilting trains.
If the OP wants to learn more they should research the two thirds rule for cant they will explain the cant equilibrium and cant deficiency and cant excess.

The last point is the rate of gain or rate of change if the OP wants to look it up. Again tilting trains on WCML have a higher rate of change than non tilt trains.
Off memory its 35mm per second or 55mm per second for WCML

 

[furnessvale]

Correct - max cant 150mm / 6’’

For the record, years ago we were permitted 7" cant on certain curves between Penrith and Carlisle.

 

[Boodiggy]

For the record, years ago we were permitted 7" cant on certain curves between Penrith and Carlisle.

There were other sections too, like Watford but they went back to 150mm.

 

[Ken H]

For the record, years ago we were permitted 7" cant on certain curves between Penrith and Carlisle.

What happened to the rail/wheel interface when you ran a heavy freight train over that at under 50mph? They must have heard the flange squeel in Keswick!!

 

[Senex]

For the record, years ago we were permitted 7" cant on certain curves between Penrith and Carlisle.

Wasn't there / isn't there a higher figure than 150 mm on the curves between Cullompton and Hele on the way to Exeter?

 

[Ploughman]

If you want the official training session, about 20 years back it was a solid 2 weeks in a classroom in Derby.
Finishing off with a 6 hour open book exam with answers provided.
And you still ran out of time.

 

[swt_passenger]

I would like to be able to measure curves radius.

I often travel over the 25 mph (uncanted) rail curve on the London side of Southampton station & fantasise about how, using railway land on either side, they might be raised to 40 mph..probably saving a minute each for 8 passengers trains an hour.
That is 800 passenger minutes saved an hour, 14,000 passenger minutes saved a day. 70,000 passenger hours saved a year.

I reckon(from sight) the curvature is no tighter then the 45mph(canted) curve on the four tracks between Clapham Junction & Battersea Park which you see from the Southampton train after Clapham Junction.
I want to compute if I am talking rubbish by measuring these curves on a map.
But exactly how, with just a ruler?

I just had a look at this using OS maps and I reckon your estimation that they’re similar is way out.

The curve you see on the right hand side north of Clapham Jn taking the Southern tracks towards the overbridge over the SWML is about a 650 yard radius. The length of the bridge over the SWML is then straight, and between that bridge and Battersea Park station it is a slightly gentler curve of about 800 yard radius, (if not more). As I noted earlier the Southampton curve is only about 200 yard radius. So they’re different by a factor of between 3 and 4…

 

[zwk500]

Anybody have access to the 5 miles that could check if the Curve Radius is marked for the relevant sections?