Steam & Excursion > 12 Degree Curve for steam locos

How sharp is a 12 degree curve for steam locos? I was looking at a track diagram for an industrial branch that had an "S" curve with 12 degree curves on both legs. In the old days it appears the largest power used were 4-4-0's and 4-6-0's. After those engines were retired they used 0-6-0's until the branch was abandoned during WWII. Can anyone give me a perespective of how sharp a 12 degree curve is? What would be the largest steam power used on such a curve. Would eight coupled engines be able to negotiate it?

As an order of magnitude, a 12 degree curve is an arc with a 500 foot radius. Even today this is about the limit for long cars (89').

On an industrial lead, that wouldn't be hard on a small locomotive. Even large locomotives could probably handle that degree of curvature on a wye.

The D&RGW narrow gauge had lots of 20-degree curves, and their 2-8-2s were designed to cope with 24-degree curves. But you don't take sharp curves like that at speed - at least not on the rails.

JAC

You can easily make a close calculation of the radius of a particular curve by the following formula:

A 1 degree curve has a radius of 5,730 feet. Thus a 10 degree curve has a radius of 573 feet and a 12 degree curve would have a radius of 477 feet.

Because the rounding error in the 5730 foot number (actual number is 5729.65)causes the resulting calculation to be slightly bigger you should round down at the half foot point instead of up.

The curves approaching the Steel Bridge in Portland, OR are 16 degrees (sharpest main line curves on the traditional SP and UP systems). SP and UP 4-8-4s regularly traversed these curves under ~10mph max speed restriction, although I heard UP did not like to operate their Northerns there. UP regularly ran their 4-6-6-4s on Portland-Seattle passenger trains around these curves as well.

In later years, 89 foot TOFC flats regularly traversed these curves (SP-BN intermodal traffic), but thanks to the mergers, not much of that occurs nowadays.

Properly spiralled, properly speed-restricted and with sufficient clearances, long cars can make it around such curves. But it is obviously not very desirable.

The real problem for long cars are sharp crossovers and reverse curves. There was a #10 crossover in front of East Portland Tower, in between the legs of the double-track wye feeding the Steel Bridge. On several occasions, 89ft auto racks or TOFC flats were derailed when trains were routed through this crossover.

Best regards,

Rob L.

Best regards,

Rob L.

The sharpest curve on C&O's main line was (still is!) nearly ten degrees, near Hawk's Nest, West Virginia. I can't remember whether their 2-10-4s ever ran there, but eight-coupled Super-power steam would have been fairly routine.

Thanks for the info folks. This was the Wabash Stroh Branch from Helmer to Stroh, Indiana. A friend of mine who is almost 90 made his first paid trip on the branch with Wabash 0-6-0 519, October 26, 1939. The train was run west from Montpelier, Ohio with the loco running tender first. He said the right-of-way on the branch was overgrown and had the profile of a "wash board". They also had sharp curves and he said the rail was light and you could feel about every joint as the track suffered from severe deferred maintenance. They serviced a pickle plant, coal dealers, stock pens, a mill and, of course, the Portland Cement company at Stroh, the reason the branch was built in the early 1900's. They wanted to run the loco backwards on the way out so that coming back the loco would be running forward in the dark with a good headlight. Attached is an early postcard view of a mixed train at Stroh. The branch was abandoned in 1945.

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10-degree curves are common on mountain main lines; any steam locomotive would have to be able to handle that (except maybe the 4-12-2s). Here and there sharper ones appear; last time I looked the sharpest curve on Donner Pass was an 11-degree, and of course Cantara has always been a 14-degree, with SP 2-10-2s and 73-1/2-inch-driver 4-8-4s (and occasional 80-inch?) running over it daily.

Dividing 5730 by the degree of curve gives a good approximation to the curve radius; to be more exact, divide 50 by the sine of half the degree of curve. That's chord definition, traditionally used on railroads; so a 10-degree curve is actually 573.686 ft radius.

Virginians 2-10-10-2,s were built for 12 degree mainline curves.

Union Pacifics 4-12-2's could handle 20 degree curves on roundhouse service tracks, and the 4-8-8-4's were designed for 22 degree curves, but neither of these, of course, at road speeds.

wabash2800 Wrote:
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> Can anyone
> give me a perespective of how sharp a 12 degree
> curve is?

There is a way to estimate (roughly) how sharp a curve is. However, you will need to know how long the rails are, or what the distance between plant welds are in CWR.

Sight a line from a joint in the outside rail in a curve that just touches the gage line of the inside rail, and continues back out to the outside rail. Count the joints or the welds between the two points on the outside rail. A 12 degree curve will have slightly less than 3-1/2 rails between the two points.

I have a table of degrees of curves and rail lengths if anyone is interested.

DAW

> A 12 degree curve
> will have slightly less than 3-1/2 rails between
> the two points.

Ahhhh....that would be 3-1/2 >> 39 ft. << rails.....

DAW