Curve radius?

[tukayaway]

I've tried searching and I still haven't found exactly what I'm looking for as I'm trying to build a UK route and want to be as accurate as possible.

In some of my depots and yards, I have a few points that have a radius of 80 using the radius tool. I also have a tight curve that hugs a hillside with a radius of 130 on the mainline. I've run trains round the hillside at 30mph and it seems ok, and yards generally have a speed limit of 20mph. But I love playing with the 9F's from the S&C pack and want something they can safely run on!

 

[cascaderailroad]

I assembled many segments in a circle of: FT Track 200m Radius for laying the spline points of the Horseshoe Curve.

I slide these circles of FT Track off to the side, and save them on my painters pallet of assets and textures, for reference and future use.

 

[ray_whiley]

This is also how I often lay curved track - the advantage being that you do not end up with a fixed radius but with transition curves as on the prototype.

But I hadn't thought of saving them and other useful assets on a palette - a very good suggestion.

80 metre ruling radius is very tight for large mainline locomotives.

Ray

 

[Jerker]

G'day tukayaway,

Indeed, I agree with ray_whiley; 80 meters radius, although used as part of a point, is still a very tight curve for mainline locomotives. If you use the 'conversion' formula that I do to convert meter radius to the more common English measurement of chains for radii, that gets you a 4 chain radius curve (radius in meters/10/2 or if that seems too difficult a math problem for you, remove one '0' from the right hand side of the figure and then halve the rest of it), which, here in Victoria Australia, would have a speed limit of 8 KpH (5 MpH) imposed on it for all traffic (and just happens to be the minimum radius allowed on the system)...

Jerker {}

 

[geophil]

Minimum radius on German standard gauge railways is 180m (6 chains). Tightest turnout is 190m. Speed limit is 40kph.

 

[backyard]

Bump-post on my thread...please...!

Hello Tukayaway!

Here is a Conversion Guide for Curve Radius.

The chart is a picture, save it to your computer.

I hope it helps!

 

[geophil]

A curve in degrees. This American notation always confuses me. Giving only the degrees is an incomplete definition. The angular measurement also requires a second parameter, a scale basis which is often omitted but essential. For the American railroad curve in degrees this means that the angle is measured per segment length of 100 ft.

Knowing about this second parameter you can put up a simple trigonometric equation:

sin (alpha / 2) = (s/2) / r

with alpha as the "curve degrees", s the reference length of the segment (100 ft) and r the radius (in ft).


Radius r in ft from curve degrees, with segment length s = 100 ft:

r = s / ( 2 * sin (alpha / 2))


Curve degrees alpha from radius r in ft, segment length s as above:

alpha = 2 * arc sin ( (s/2) / r)


Example: 20° convert to 288 ft

 

[Pencil42]

Thanks Geophil! Note that 100 ft is also the length of our surveyor chains; which is probably where that measurement came from.

Curtis

http://carsoncarshops.com/images/ghosts/gold_hill_depot_05.jpg

 

[ray_whiley]

In the UK a Surveyor's Chain is 100 links and 22 yards - hence the length of a cricket pitch. 10 chains = 1 furlong, 8 furlongs = 1 mile. None of this metric nonsense!

Ray

 

[backyard]

Roland & Ray got the best of me here....

I knew when geophil posted a reference in chains I might be a lost dog in high weeds....

...but I posted anyway.:hehe:

Thanks geophil for your clarification about proper curvature calculation!

Ray, your revelation of thought on the metric system is new to me, I thought everyone wanted me to drop the US-American & adopt meters...:wave:

 

[ray_whiley]

Confession time - I use both metric and imperial. As heights in Trainz are always metric, this is most convenient for creating buildings, splines etc. and avoids a lot of conversion work. But imperial means more to me in real life: I understand temperatures F much better than temperatures C, for instance. And miles per gallon better than kilometres per litre - or whatever it is. And there are many in the UK who think the same - which is why weather forecasters often give the F equivalent for temperatures they have quoted. For modelling, I'm happy using either as occasion demands - probably after many years of mixed systems like OO scale (in the UK) being 4mm to 1 foot.

In any case what could beat the beauty of such measurements as : 12 pence to one shilling, 20 shillings to one pound. Or rods, poles and perches. 20 fluid ounces one pint, eight pints one gallon. I'm sure that using these at school (long before the UK joined the EU and decimalisation came in) made for greater mathematical ability.

Ray

 

[geophil]

As heights in Trainz are always metric

Internally, Trainz is completely metric.

In any case what could beat the beauty of such measurements as : 12 pence to one shilling, 20 shillings to one pound. Or rods, poles and perches. 20 fluid ounces one pint, eight pints one gallon. I'm sure that using these at school (long before the UK joined the EU and decimalisation came in) made for greater mathematical ability.

In cartography British Ordnance Survey went metric in the 1930s (!). It seems, initially, they didn't dare to tell the people that the obscure numbers in map coordinates are simply metres and that the letters denote squares of 100 x 100 km.

 

[RPearson]

A curve in degrees. This American notation always confuses me. Giving only the degrees is an incomplete definition. The angular measurement also requires a second parameter, a scale basis which is often omitted but essential. For the American railroad curve in degrees this means that the angle is measured per segment length of 100 ft.

Actually there is a 3rd part to this which is also usually left out. Whether the segment length of 100 ft is measured along the arc or along the chord of the circle. For large radius curves the difference is negligable but for small ones it isn't. In the US the chord method which you provide formulas for is used more often by railroad surveyors and the arc method more often by highway surveyors.

The arc method is simplier of the 2 to calculate.

For the arc method we have the arc length of 100 ft = 2 x pi x R x D /360 with R the radius of the circular arc in ft and D the degree of curvature in deg. This gives us R x D = 5729.58 which is often rounded to 5730. So R = 5729.58/D and D = 5729.58/R. Both of these are also often used for approximations of the chord method when the radius is large.

The survey maps I have for the EBT RR were drawn in 1919 for ICC valuation purposes and use the arc method to define the degree of curvature. The EBT was surveyed and built in 1875-1876 period. I'd assume the 1919 maps followed the originals in defining degree of curvature but I can't say for sure. The EBT is a 3 ft ng RR with a number of the curves having relatively small radius and the difference between the two methods is not negligable for many of them.

Bob Pearson

 

[ray_whiley]

In cartography British Ordnance Survey went metric in the 1930s (!).

True. But UK road atlases - at least all I have seen - are still inches to the mile. And car performance is usually quoted as miles to the gallon. I think our resistance to being completely metric is perhaps a hangover from our opposition to Naploieon!

But I agree that for Trainz, it is better and simpler to stick to metric.

Ray

 

[cascaderailroad]

Since we have Radius Gauges in Trainz ... all the cyphering is unecessary. There are no chains nor furlongs in the Trainz ruler ... learn the metric system and simply lay a curve.

If you have a backwoods NG line you can use 50m-75m radius FT Track as a gauge and spline point placement guide ... or for high speed modern lines use 200m-600m radius gauges.

 

[legia]

Minimum radius of an arc

In my routes, which have standard gauge of 1435 mm, I set minimum radius of an arc as 200 meters. In exceptional conditions, I lower this value to 180 m, but only in additional tracks like the ones connecting a turntable. The reason for it is that some locomotives, like the ones with Co-Co axle arrangement, won't negotiate arches tighter than 150 m.

For connecting additional tracks on a station I use tracks with radius 200-300 m
For connecting sidings and industries: 250-400 m.
For local branch lines: 500 m (max. speed 35mph), 600 m (max. speed 40 mph). Value of 600 is critical, because it is practically impossible to weld the track in a tighter curve.

For secondary lines of speed up to 50mph I set minimum radius for 800 m.
For primary lines:
1200 m max. speed 60 mph
1500 m max. speed 65 mph
2000 m max. speed 70 mph
4000 m max. speed 100 mph
8000 m max. speed 200 mph

Keep in mind that anything lower than 1500 m results in premature wear and tear of the rolling stock.

In turnouts:
Max. speed 20 mph, 6 degrees, 190 m (in additional tracks) or 300 m (in main tracks)
Max. speed 40 mph, 5 degrees, 500 m
Max. speed 50 mph, 4 degrees, 800 m
Max. speed 60 mph, 3 degrees, 1200 m

In TC, TS2009 and newer versions, which allow retaining 0.1 degree accuracy after turning a fixed track, I use turnouts with finer angles: 6.3, 4.8, 3.1, but the same radius.