Western Railroad Discussion > track engineering question

How big of a radius would a loop or balloon track (slow speed) in a yard need to be?

I should know but I don't, so I appreciate any insights.

Probably around 400 ft.  The baloon tracks at Blue Canyon and Truckee on Donner Pass are around that.

Stan Praisewater

sagehen Wrote:
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> Probably around 400 ft.  The baloon tracks at
> Blue Canyon and Truckee on Donner Pass are around
> that.
>
> Stan Praisewater

Thanks. So 400' radius, or 800' diameter.

Making a first pass at a concept that I am working on.

You still need spirals to go in and out of the curve, and a tangent for the reverse curve.

Stan

Posted from iPhone

sagehen Wrote:
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> You still need spirals to go in and out of the
> curve, and a tangent for the reverse curve.
>
> Stan

Thanks again Stan.

The Tehachapi Loop (Walong) in HO scale is about 110" radius.

HardYellow Wrote:
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> The Tehachapi Loop (Walong) in HO scale is about
> 110" radius.

That's interesting. I specified yard low speed, but Tehachapi is mainline with grades. Not the highest speed, but not yard. Anyhow, from the 110" radius in HO, i calculate about 1600' in diameter actual.. That is about twice the yard estimate.

Anybody know what the radius of the balloon track at West Colton Yard is?



Edited 1 time(s). Last edit at 06/20/24 15:41 by PHall.

PHall Wrote:
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> Anybody know what the radius of the balloon track
> at West Colton Yard is?

Trying to scale it from a satellite view, I get it in the 400' radius ballpark.

ts1457 Wrote:
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> PHall Wrote:
> --------------------------------------------------
> -----
> > Anybody know what the radius of the balloon
> track
> > at West Colton Yard is?
>
> Trying to scale it from a satellite view, I get it
> in the 400' radius ballpark.

10 degree curve, it I remember correctly - 573 feet.

TAW

ts1457 Wrote:
-------------------------------------------------------
> PHall Wrote:
> --------------------------------------------------
> -----
> > Anybody know what the radius of the balloon
> track
> > at West Colton Yard is?
>
> Trying to scale it from a satellite view, I get it
> in the 400' radius ballpark.

The balloon at Lake Yard in Portland looks to be a little shy of that, maybe 380 feet.

The Coach Wye in Seattle is 16 degrees if I remember correctly - 358 foot radius. It is used regulary by Amtrak and now and again by 85 foot intermodal cars with six axle power.

A No 7 turnout, the sharpest I have encountered is 365.6 feet.

TAW

A 14 degree curve is 410.38 feet radius.

The curve within a No. 8 turnout is 12 degree 30 minutes.

The sharpest ng wye is 24 degrees which is 238 feet radius.

A 20 degree curve is 287 feet radius
You don't need to figure in any spiral for that yard speed. 

PlyWoody Wrote:
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> A 14 degree curve is 410.38 feet radius.
>
> The curve within a No. 8 turnout is 12 degree 30
> minutes.
>
> The sharpest ng wye is 24 degrees which is 238
> feet radius.
>
> A 20 degree curve is 287 feet radius
> You don't need to figure in any spiral for that
> yard speed. 

PlyWoody, appreciate it!

TAW Wrote:

> 10 degree curve, it I remember correctly - 573 feet.

That's right:  the engineering formula is R = 5730 / D, where R is the radius in feet and D is the degree of curvature.
Maximum curvature on mainlines is about 16 degrees, or 358 foot radius.  Agree with the other poster who said no transition spiral needed in the yard.

TAW Wrote:
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> The Coach Wye in Seattle is 16 degrees if I
> remember correctly - 358 foot radius. It is used
> regulary by Amtrak and now and again by 85 foot
> intermodal cars with six axle power.

Is that before or after the new Main 1 was installed?  That part of the north leg from at-the-time new Main 1 to the used-to-be-there diamond was relaid new.  19 degrees is what I seem to remember for that part of it.
 

MP555 Wrote:
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> Is that before or after the new Main 1 was
> installed?  That part of the north leg from
> at-the-time new Main 1 to the used-to-be-there
> diamond was relaid new.  19 degrees is what I
> seem to remember for that part of it.
>  

It was 16 when I designed the track arrangement. I didn't get a new drawing afterward, but dim memory tells me that the wye wasn't changed except at the turnout, but I don't remember how they did it.

TAW

You check any cuve with a 62 foot long chord and measure it every 31 feet.  The length of the offset in inches is equal degrees.