Rail car sway

[Anonymous]

What causes a rail car to sway while its goin down the track? Can it sway so bad that the car and subsequently derail the train? Do empties do it more than loaded or vise versa or the same? Are their certain types of rail cars that are more prone to swaying?

When ever I catch the WSOR or the UP, it seems like the grain cars are the ones doing it the most. Sure would hate to see one of those cars fall over while at a crossing.

[mudchicken]

Combinations of truck hunting and track cross level problems creates harmonic "rock & roll". (neither may be a defect on its own, but in combination creates havoc)

Well documented that this is the most critical between 9mph and 16mph where wheel lift comes into play because of maximum yaw...

[JoeKoh]

Rail cars have a natural rocking motion but grain cars are notorious for loads shifting. just ask the I&O crew that switched a grain car in hamler ohio.
stay safe
joe

[Anonymous]

Loco's sway too, depending on conditions.

[CShaveRR]

The car length had a bit to do with it, too. You're right about grain cars. Pullman Standard's 4750-cubic-foot covered hopper, arguably the most popular covered hopper design ever, had the misfortune of having a wheelbase close to the 39-foot length of a regular length of rail. This was enough to create harmonic swaying.

A loaded car would be the more likely to tip, due to the higher center of gravity.

[Anonymous]

Track conditions including joint spacing, cross level, tie condition, gauge, train speed and car loading/lading all are factors affecting car rocking. At higher speeds truck hunting may also be a factor...

LC

[daveklepper]

Question: track where you notice the problem: jointed rail or welded rail?

The dynamic stiffness of rail at the joint is far less than in the center between joints. If undermaintained, jointed rail will develop low spots at joints and high spots in between. This is one reason Europeans use (used?) opposed joints instead of the US practice of staggared joints. The USA approach is supposed to reduce wear. But with undermaintained track it will set up some rocking motion in any car or locomotive. And if the natural frequency of the suspension is the same as the frequency that the wheels meet the joints or even a harmonic (twice or three times, etc). then watch out. Some engineers know there are particular track sections where one must never run at a particular speed with particular equipment. Dave

[Hugh Jampton]

Lower sway or upper sway?

[jchnhtfd]

The natural harmonic motion of a car is influenced by its height above the rail (actually, the height of the centre of gravity) more than anything else... as mudchicken points out, if that natural rocking motion is more or less in the same frequency as any truck motion, you've got a problem. As he says, 9 to 16 mph is usually the worst, and covered grain hoppers, with their high centre of gravity, are particularly affected. And yes, it is quite possible to rock and roll a car right off the track. As Dave says, though, experienced engineers know where there will be problems...

[Anonymous]

At one time the UP had a rule on the high line (Bieber-Keddie) that stated that if a train could not maintain 16 MPH or more then it had to reduce speed to 10 MPH to avoid harmonic rocking. This line has had a lot of maint. done on it recently and is now in the BNSF camp. So I don't know if it's still in effect.

[tree68]

I remember standing on the platform of the IC station in Rantoul, Ill, wondering if the locos coming down the track were going to sway a little too far in my direction. The roadbed there was in pretty poor shape, and the engines did do some pretty good swaying.

[Anonymous]

BNSF limits empties to 55mph for this reason. Years ago, I'm told, they installed an under-car camera and found that some cars were literally "flying" off the tracks at speed. So they came up with the empty rule. So, when we get our train profile, we check for empties. I hate getting an otherwise 70 mph intermodal train with just one empty in it...55! Samd.

[kenneo]

A number of years ago, an SPS freight went into emergency along the Columbia East of Wishram. The crew was real mistified about what had happened because there were no busted knuckles or drawbars missing. No cars were found to be derailed. But one car was missing and never found when the mud-hop rolled the train at Wishram and when the train was switched at Vancouver.

Several years later, when a low water year caused the river to be drawn down, guess what showed up! This car, an empty, had literally lept out of the train and into the river - and not just into the river, but far enough out that it took a 20 foot lower river level to show the top of the car!!

When I was working at Medford in the ear.y 1970's, the track in front of the depot had mudded up so bad that the tamper could not give a level after only it had run over the area. The Plate C cars - which were new, then - are the worst on this typed of trak and with this type of problem, and the Plate C box cars would actually lift all the wheels of each side completely off the track at 8 MPH. Go someplace else? Not when you're the Telegrapher/Mud-hop and have to roll the train doing both jobs. Climbing down rat-holes in Viet Nam after Charlie was not as scary as this.

The SINGLE most important criteria is the truck spacing and the rail length on jointed rail. As has been well described by others above, when the truck centers and the rail length are the same or very close thereto, LOOK OUT. Center of Gravity is next in importance. The higher it is, the more rocking you get. Then whether it is a load or an empty. Even excellent cross-level can fall prey to these problems in 36' and 39' rails. 39' are the worst since the truck centers on a Plate C car are at 39'6" (that is the number I remember, anyway) most of the time.

And covered hopper cars have the highest center of gravity of all car designs.

[Anonymous]

QUOTE: Originally posted by daveklepper

Question: track where you notice the problem: jointed rail or welded rail?

Im new to this hobby, so honestly I dont know the differences from a exterior point of view. Sometimes when I notice the swaying of the cars is on the WSOR line from Janesville to Milton Wisconsin, just as they cross HWY 14. Thats the line where they upgraded to welded rail recently. When it comes to the UP, I dont know what kind of rail they are using where I catch them.

Thanks for the info to my question.

[kenneo]

To 5penniesworth --- If I understand you correctly, you are looking at jointed rail that has been relaid with welded? If the ballast was not cribbed properly, the low spots where each rail joint was prior to the relay would still be there, and the rock and roll would continue.

What railroads usually do is to raise the low spots (fill the spot with ballast and tamp just the low spots) to bring the surface back into specification and then repeat as often as necessary until the low spots refuse to become low spots anymore - if they ever do. This method is considered cheaper because it lowers the original relay projects costs but does require continued spotting to be done over what can be several years time.

My personal opinion is that once you start getting low spots, you get fouled ballast and that causes one of the main reasons for using ballast in the first place to fail - drainage. It is not long before you are running on a raised mud pile. Cribbing, therefore, which totally removes the old ballast and replaces it with new is the only practical solution - and it totally removes the low spots.

[Anonymous]

Another factor in car sway is side bearing clearance. Each truck has two side bearing points (just large steel blocks) that allow the car to sway independant of the truck. This is supposed to keep the car and the truck from swaying together, which will cause the car to tip over. I believe the side bearing clearance should be kept at about 1/4" or 3/8", but have seen may with no clearance and many with clearances over 1/2".

Another reason covered hoppers are a problem is the grain that they carry acts like water when going around curves, shifting back and forth. If a train gets going to fast around a sharp curve all the grain runs to one side of the car and can tip it over. This is what happened a couple months ago on La Veta Pass. Now run by Rail America, the crew lost control of the train going down the 3% grade on the east side of the past and the shifted grain tipped 17 cars off of the rail and down the side of the mountain while the locomotives stayed on the rail without any problems

[Noah Hofrichter]

5pennisworth, the way, I'm told to tell jointed from welded rail, is the fact that the WSOR laid the rail in 1/4 mile sections, so you won't see joints every 36 feet or so in the rail. just my understanding.

Noah