This month’s Trains Magazine has an article about a shortline grain hauler in the OK/TX area. Because of poor track conditions, operation is limited to 10 m.p.h. on the line. The article goes on to say, that because of the 10 m.p.h. track conditions, trains are limited to 25 loaded hoppers and 2 Geeps. How would track conditions limit the length of the train?
A fully loaded, 263,000-lb. covered hopper when moving over old 90-lb. rail will actually cause the crystalline structure of the railhead to momentarily “go plastic” and flow ever so slightly.
The force of 16 powered wheels (eight from each of two Geeps) applying tractive effort on an ascending grade with maybe 3350 to 3400 gross tons in tow (plus the weight of the two engines) may be the limit of what the track structure can handle. And it’s not just the rail either.
Thin angle bars applied to each track joint that have withstood decades of momentary stresses as trains pass over them grow brittle with age. And at low joints, the stresses are magnified.
Consider too that if the roadbed is soft, if the surface and alignment of the track is poor, and the crossties are weak that means that the rail itself carries more and more of the responsibility of carrying the train. If rail is handling loads that come close to exceeding the design endurance of the steel, any extra forces generated by faster speeds accelerate the possibility of a rail breaking.
Lastly there’s the condition of “rock-and-roll.” Loaded covered hoppers with a relatively high center of gravity, when moving over 39-ft. sections of jointed rail, tend to sway laterally. This side-to-side motion maximizes in the 15-to-18 mph range. And if a train moving in that speed range has a lot of loaded hoppers of similar design coupled together, a harmonic motion, transmitted through each drawbar and coupler, develops among the cars. The harmonic motion, in turn amplifies the sideways “rock-and-roll” thus accelerating the possibility of one or more cars literally wal
Two other items to add. The weight of the cars cause the trucks to sit in a small depression in the track. This causes the locomotives to actually be pulling the train up a grade since the train is always trying to climb out of that hole. The second point is that when the train goes into a dip, instead of the train being able to push itself up the grade on the other side, the locomotives have to actualy tow it out, so either extra power needs to be added or the train needs to be going faster to push itself out of the hole. I’m suprised that they are using 4 axel power with that sort of tonnage at that speed. I would expect 6 axels with just 2 units.
This is the only reason that resonates for me. On a 1 % grade, the locomotives would have to exert a tractive effort or force on the rails of 33.5 to 34 tons = 67,000 to 68,000 lbs. If the train were longer, that force would be proportionately greater, and since it is concentrated at the head end, could be more than the track structure can handle.
All of the other reasons are valid, but it seems to me that either the 25-car limit doesn’t really address them, or those concerns are more affected by the total number of cars going over the track than by the number of cars in a particular train.
I even thought that it might be a ‘damage control’ measure - if there is a derailment, no more than 25 cars would be involved. But at only 10 MPH = 15 ft. per second or so, the train would stop fairly quickly anyway once the train air line was severed or the train is placed into emergency - I’m guessing maybe within 5 carlengths, 10 at the most, so that doesn’t seem to be the reason.
- Paul North.
P.S. at 9:30 AM - Perhaps this limit is empirical = derived from bad experiences, such as several derailments of longer trains that happened somewhere behind the 25th car. Similarly, in the 1980’s there was a 2-part article in Trains about KCS, and one portion was about the mid-train SD40 slave or helper units - what are now DPU operations. After a series of derailments, the boss ma
Paul:
(1) Anchors? What anchors? (Rhetorical question…wanna see that rail run out under the powered axles like so much spaghetti?
(2) You do NOT want 6 axle locomotives out on a lightweight track section for the #1 reason above and also because of high L/V lateral forces in curves with ties near the end of their service life. Anyone running 6-axle power on branchline track in poor condition is buying trouble.
Although I do recall seeing a picture in Trains years ago of a train crossing a diamond. In the caption was the phrase “pitter patter of A1A feet” or something to that effect. The locomotives (ALCOs?) were A1A-A1A and were used because of some light loading issues on that particular line. If the bridges were that light, I’d imagine the tracks were, too.
I seem to recall that the Milwaukee and the Canadian roads bought some ‘lightweight’ SD-7’s and/or SD-9’s for some of the Grainger lines to reduce wheel loadings of the locomotive account their bad track conditions.
SD’s of course would be C-C-C trucks. A-1-A trucks would be found mostly on E8’s and PA’s but I believe FM had an A-1-A trucked locomotive. (A-1-A, for defnitiion, means the A axels were powered and the 1 axel was not; thus C indicates all three axels are motored and B the two axels are.)
The MILW’s were 10 SDL-39’s - C-C’s, but with the weight of a only B-B - 250,000 lbs. instead of the more normal 360,000 lbs. of the SD39. Here’s a link to a webage with an image and lots of details: http://www.thedieselshop.us/Data%20EMD%20SDL39.HTML
There apparently were also GMD1’s and GA8’s with C-C trucks that went to Candian railroads - see http://www.thedieselshop.us/Data%20EMD%20GMD1.HTML and http://www.thedieselshop.us/Data%20EMD%20G8.HTML
I believe the Canadian units were ALCo RSC-13’s - http://www.thedieselshop.us/DataRS-13m.HTML - and RSC-24’s - http://www.thedieselshop.us/DataRS-24.HTML - with the A1A trucks. Later, RS-18’s had those trucks installed under them and were de-rated to make RSC-14’s - http://www.thedieselshop.us/DataRSC-14.HTML - see http://en.wikipedia.org/wiki/MLW_RSC-24 and http://en.wikipedia.org/wiki/MLW_RSC-14 for the details.
CN’s GMD1’s had A1A-A1A trucks (1000 series) and B-B trucks (1900 series) as built. They also had some G8’s with similar arrangements (no C-C trucks)
The only GA8’s in North America were in Mexico on NdeM, Unidos de Yucatan and Coahuila-Zacatecas. They had two traction motors mounted in the carbody connected to the axles by drive shafts and u-joints. Some still serve as yard switchers on FCAB in Chile.
Trying to shove a B-trucked EMD locomotive with two axles spaced 9’-0" apart is a lot easier than a locomotive with EMD C-Trucks at 13’-7"+ spacing (plus the intermediate axle)
- GE’s have 9’-0" & 13- 7"1/2 and Alcos 9’-4" & 13’-0" respectively.
IIRC, those MILW SD-39’s were not using a conventional EMD “C” Truck either (and a shorter frame so they could turn easier)
Those C-truck flanges are pushing hard on the ball of rail! I don’t want to see what the rail cant on that outside rail looks like with old worn ties.[X-)]
(using second generation locomotives here as reference)
If you have lightweight railroad with less than 90# rail and low number (single digit) turnouts, you most certainly are buying headaches. If you think a 3 axle truck tracks & turns as easilly as a 2 axle truck, have you bought that oceanfront property in Arizona yet?[:-,]; IF you have more curve than tangent, do you have any hair left after running those 6-axle units?
MC,
Sounds like you’re speaking from some very painful experience.
- Erik
CN in Canada ultimately had five types of A1A branchline power. First were 30 H-12-46s of CLC/FM design. Several years later 35 RSC-13s of MLW/Alco design were added. These were essentially RS-1s on 6 wheel trucks. A year or two later saw the the addition of 78 GMD1s from GM. About the same time, MLW built 4 RSC-24s using a derated 244 prime mover from FPA-2s that were rebuilt with 251 engines. The 5th type was a kitbash, taking the trucks from the worn-out RSC-13 and RSC-24 fleet and putting them under derated RS-18s. All are now retired.
The goal was light axle loadings, since CN was plagued with many branchlines with 60 pound rail, and probably matching bridges, from its predecessor roads. The lighter footprint permitted a higher speed limit on the flimsy track structure. Many of their normal road power, such as the GP9s, had smaller fuel tanks and other options to keep the weight down. And partly in this category were the 6 A-B sets of CLC/FM CPA-16-5s, with a B-A1A configuration. Again, the extra axle was to keep the axle loadings down.
Two other Canadian roads also had some A1A power. The Northern Alberta Railway had a small fleet of GMD1s, for the same reason as CN. The second was the Pacific Great Eastern (later renamed British Columbia Railway). The PGE bought a group of RSC-3s, presumably because of concern over the track. Since they also had 2% grades, it was not long before they were retrucked with standard AAR-Bs, making them normal RS-3s to all intents and appearance. One has now been preserved at the West Coast Railway Museum in Squamish (north of Vancouver BC) in its original configuration, using trucks acquired from CN’s fleet.
Back to the original topic, I wonder if the 25 car limit might be to keep the lateral stresses on curves down. If the tie condition is marginal, it becomes a lot easier to roll a rail.
The C-C arrangement was very rare in Canada at
I thought the author could have told us how a wheat line that “sits dormant most of the year” crews its trains during the rush. Or does the help go dormant too?
In the early 1980s, while poking around the Soo Line yard in Bismarck, No. Dak., I discovered that certain tracks were laid with 85-lb. WELDED rail! Not only that, but the track bolt holes that should have been in the rail web were missing as well. Apparently the railroad was cutting off the battered ends of each rail before welding shorter lengths of rail together.
I don’t recall seeing any 100-ton capacity grain cars on any of the Soo Line tracks that day, so maybe 85-lb. welded rail was adequate for an operation that required only 40-ft./ 70-ton capacity boxcars for grain loading.
Flash-butt welders will fuse anything. Been around lots of SH-90# CWR as well…in a straight line it’s OK…the fun is around curves and turnouts plus the fact that finding anchors, especially new anchors that small, is next to impossible. That stuff is gonna run!
I was under the impression that the 25 car limit was as much an operational restriction, as in no sidings or yard to handle longer cuts as it was track structure.
The subdivision in question may have been built with sidings, and perhaps many decades ago more than one train operated on the territory during a calendar day. Today, though, the territory probably sees no more than one crew and one set of power on any calendar day, so I doubt that having sidings long enough to where one train can meet a second train is really an issue.