Questions about track curvature requirements.

What is the minimum recommended curve radius (in feet) for each of the following pieces of American standard-gauge rolling stock?

Locomotives

1. GM/EMD SD40-T-2, 3-axle trucks
2. GM/EMD GP38-2, 2-axle trucks
3. Baldwin Consolidation 2-8-0 steam engine with Vanderbilt tender as used on SP circa 1900-1935


Cars

1. modern double-decker autoracks as used by UP
2. Pullman heavyweight coaches, circa 1915

Hmmm…
The steam locomotive… I have some ideas of places to look, and will get back to you if I find something relevant.
As for the diesels…
In this case, George Elwood's marvellous "Fallen Flags" rail image site is your friend! One of the documents reproduced there is a 1989 Conrail locomotive diagram book, with basic data on all CR's classes of locomotive. Minimum curvature requirement is one of the facts the mechanical department had a space for on their forms.
For the SD-40-2, minimum curve is 193 feet radius (= 30 degree curve). This, however, is only for moving the locomotive around in a yard or engine terminal: it applies only to a single locomotive, operating alone. Couple it to a car, or lash it up with another unit, and the requirement is 359 feet (= 16 degree).

(Possible glitch: Conrail's SD40-2 locomotives were delivered with non-standard trucks: trucks like those on earlier EMD C-C units instead of the HTC truck introduced with the Dash-2 line. This might have some effect on the curvature requirements… but I suspect not a big one compared to the approximate nature of the figures!)

For the GP38-2, it's 140 feet (= 42 degree) as a single unit, 301 feet (= 19 degree) when coupled to another car or locomotive.

The comparable GE models (C30-7, B23-7) are quoted with slightly better characteristics: able to pussyfoot around sharper corners. Though I don't know whether this reflects a real difference or whether it is a matter of GE's engineering staff being willing to tolerate louder flange squealing, and run a higher risk of derailment caused by overturned rail, when they figured out the curve requirements for their locomotives.

I have a feeling that the precise numbers aren't very meaningful. Too much depends on other factors, like the track maintenance standards! At least in the steam era (when long rigid wheelbases were a way of life) to widen the track gauge slightly on curves. It may be that a locomotive that could ooze around a sharp bend on steam-era track would derail if tried on a modern curve of the same radius!

George Ellwood's site doesn't have as much on Souther Pacific equipment, but it does have a collection of Pennsylvania Railroad locomotive (and car) diagrams, and New York Central locomotive books from 1930 and 1946. The Pennsyvania's mechanical department apparently didn't record curve requirements on its locomotive diagrams, and the New York Central sometimes left this blank even though their 1946 book had a place for it at the top right corner of their locomotive diagrams (section D of the 1946 book). I noticed, however, that a number of 2-8-0 and 2-8-2 tips were noted as "designed for" 18 degree 30 minute curves: so, radius somewhat over 300 feet. … My guess is that there wouldn't have been many curves that sharp outside yards and terminals.

Allen Hazen wrote:Hmmm…
The steam locomotive… I have some ideas of places to look, and will get back to you if I find something relevant.
As for the diesels…
In this case, George Elwood's marvellous "Fallen Flags" rail image site is your friend! One of the documents reproduced there is a 1989 Conrail locomotive diagram book, with basic data on all CR's classes of locomotive. Minimum curvature requirement is one of the facts the mechanical department had a space for on their forms.
For the SD-40-2, minimum curve is 193 feet radius (= 30 degree curve). This, however, is only for moving the locomotive around in a yard or engine terminal: it applies only to a single locomotive, operating alone. Couple it to a car, or lash it up with another unit, and the requirement is 359 feet (= 16 degree).

(Possible glitch: Conrail's SD40-2 locomotives were delivered with non-standard trucks: trucks like those on earlier EMD C-C units instead of the HTC truck introduced with the Dash-2 line. This might have some effect on the curvature requirements… but I suspect not a big one compared to the approximate nature of the figures!)

For the GP38-2, it's 140 feet (= 42 degree) as a single unit, 301 feet (= 19 degree) when coupled to another car or locomotive.

The comparable GE models (C30-7, B23-7) are quoted with slightly better characteristics: able to pussyfoot around sharper corners. Though I don't know whether this reflects a real difference or whether it is a matter of GE's engineering staff being willing to tolerate louder flange squealing, and run a higher risk of derailment caused by overturned rail, when they figured out the curve requirements for their locomotives.

I have a feeling that the precise numbers aren't very meaningful. Too much depends on other factors, like the track maintenance standards! At least in the steam era (when long rigid wheelbases were a way of life) to widen the track gauge slightly on curves. It may be that a locomotive that could ooze around a sharp bend on steam-era track would derail if tried on a modern curve of the same radius!

Thanks, sir.

I have been examining the curve radii of the Mojave Subdivision in southern California in Google aerial maps with a ruler. Big long UP six-axle SD70-ACe's and such seem to clamber 2%+plus grades there with turns as sharp as 581 feet with long freight trains' being hauled. These heavy freights do squeal some in YouTube videos. If I were to construct a new freight/passenger/excursion railroad line along the banks of the Trinity River I might set my turn sharpness limit to be 600 feet and be safe to operate with my particular rolling stock I have in mind. I am wondering if those 6-axle Pullman heavyweights can handle 600-foot radius turns. I know the SD40-T-2's handle turns this sharp on a mountain line where sharper turns are common than out on the flat land. Certainly mallet 2-6-6-2's can handle these: articulated steam locomotives Baldwin once made. Always design your railroad for the specific rolling stock you have in mind observing tunnel clearances and such.

As you see, the curve at 41.2675N 122.30395W is just over 400 ft radius-- lots of six-axle cars ran over it.

Nobody knows how sharp the curve at the east end of the river bridge just east of Portland OR's station is, but far as anyone knows its radius has always been less than 400 ft.

timz--
So, is the curve you give coordinates for on a main line? At a guess, a curve right outside a station might be a bit sharper than would be tolerated elsewhere: trains would be moving slowly when they encounter it.
On the Pennsylvania Railroad, the curve at the Pittsburgh (PA) passenger station, leading onto the bridge across the Allegheny River, was sharp enough to be an operational hassle. (T-1 steam locomotives didn't like it: a real drawback for an express passenger locomotive on a railroad whose premier passenger trains went through Pittsburgh!)
The famous Horseshoe Curve at Altoona PA is a 9 degree 15 minute curve: radius about 650 feet. This IS mainline: over the years it has seen lots of Pullman cars, and still has lots and lots of six-axle diesels hauling freight around it. Speed limit (because it is on a heavy grade) is I think 30 m.p.h.
Note that one might not want to run every day over a curve as sharp as the sharpest your vehicle can do occasionally. The Monon Railroad bought six-axle C-628 diesels, which COULD negotiate the curves on its track, but soon traded them in on four-axle C-420 because they decided they would rather NOT operate the six-axle units over the curves of the south end of their line.
…
I don't know, and don't know where to look for, the curve limits for six-axle heavyweight passenger cars, but I would GUESS they aren't TOO different from those for six-axle diesels.

Allen Hazen wrote:timz--
So, is the curve you give coordinates for on a main line? At a guess, a curve right outside a station might be a bit sharper than would be tolerated elsewhere: trains would be moving slowly when they encounter it.
On the Pennsylvania Railroad, the curve at the Pittsburgh (PA) passenger station, leading onto the bridge across the Allegheny River, was sharp enough to be an operational hassle. (T-1 steam locomotives didn't like it: a real drawback for an express passenger locomotive on a railroad whose premier passenger trains went through Pittsburgh!)
The famous Horseshoe Curve at Altoona PA is a 9 degree 15 minute curve: radius about 650 feet. This IS mainline: over the years it has seen lots of Pullman cars, and still has lots and lots of six-axle diesels hauling freight around it. Speed limit (because it is on a heavy grade) is I think 30 m.p.h.
Note that one might not want to run every day over a curve as sharp as the sharpest your vehicle can do occasionally. The Monon Railroad bought six-axle C-628 diesels, which COULD negotiate the curves on its track, but soon traded them in on four-axle C-420 because they decided they would rather NOT operate the six-axle units over the curves of the south end of their line.
…
I don't know, and don't know where to look for, the curve limits for six-axle heavyweight passenger cars, but I would GUESS they aren't TOO different from those for six-axle diesels.

I have sharp curves and steep grades with southern California's Mojave Subdivision in mind through the Tehachapi Mountains. I think I used my ruler on Google Earth maps and found a 180-degree turn to be as sharp as a 561-foot radius. SD40-T-2's used to run over these daily and so do modern six-axle locomotives like the GE Dash 9's and the EMD SD70 series. This is is a slow main line in these mountains at 25 MPH speed limit in many parts, however. Is it because of the tight curvature or the steep grades which go 2-something percent? I drive my SP SD40 freights in train simulator on this sub a lot as this is my favorite line in game play with the tight Waylong loop. I haul mile-long fully-loaded trains over these twisties in train sim too.

My guess is the six-axle Pullman HW's and any articulated steam locomotive with no more than three driver axles per bogie should handle the Mojave Sub as well without too much squeal.