Hi Everyone
When I go railfanning I notice all the time that when the train passes over a switch it rocks back and forth quite alot,what causes this? and does it happen alot because it can get a little scary watching all those freight cars and loco’s sway back and forth.
thanks and I hope that somebody can answer this.
Jeremy
Hi Jermey,
I will give it a whirl.
Know what a track frog is?
Its the point where the two rails meet, a very heavy guide ways for the wheel flange to follow.
Because it is such a heavy and stouter piece of track work, and because of the way turnouts have to operate, the support under a frog is greater and more spread out than the support under the opposing rail.
Bet the train sways out, away from the center or other track first.
The frog has no “give” in it like the rail does, no ability to flex, its almost like a bump in the track.
If the track work leading up to and away from the frog isnt kept maintained well, the force of running over the frog shifts the weight of the cars and locomotive to the outside rail, which tends to have more flex.
Over time, the outside rail will begin to settle deeper into the ballest, and the problem becomes even more pronounced.
Imagine driving a car, and you run over a bump in the road, but the bump is only on one side, say the passenger side of the car.
The passenger side rises up, and the drivers side will sink down, due to the action of the suspension, springs and shock asorbers.
Same thing with the locomotive and cars, the swaying is the result of the suspension system trying to compensate for the bump, or high spot in the rail.
Sometimes it can get so bad you would swear the car is going to tip over!
Try having to stand inbetween two opposing trains on double main, both running over the frogs on their track, and watching the cars, it looks like they are going to smack into each other at times.
On second though, do not try that at all, I get paid to take that risk, you dont, and shouldnt
In fact, if you dont railroad for a living, I suggest you stay at least 50’ back from the track.
Cars have banged into each other that way.
Stay Frosty,
Ed
I recall watching a video of a steam era C&NW freight train going by, and noticing that the cars, especially the tender did an awful lot of swaying.
Jeremy:
Ed “whirls” really good! Add to that the fact that the gap in a normal frog takes a heckuva beating with every wheel that passes over it. You might liken the gap in a frog where the wheel passes over the rail to a highway pothole, except no street could survive that type of beating. On main lines, railroads are going back to using “spring” frogs where the gap is closed except when trains go off the main track. (Spring frogs have their own set of related headaches). Without a spring frog on a busy main track, you will see welders constantly adding metal to the frog to build it back up and tampers (Big yellow machines) pushing rock back under the ties to eliminate dips in the track and allow trains to operate at full speed.
Also, railroaders call the rocking phenomena (“rock and roll”, a term coined in the 1910’s!) which is at its worst between 8 and 17 mph, where a wheel on a freight car can actually lift off the rail caused by harmonic rocking of the cars. When you see trackmen walking around on the track with a funny looking bright metallic bar and stooping over every so often on the track., they are looking for cross-level or dips in the track that should not be there (that start the cars rocking) …
Please, as Ed says, stay away from the track and watch from a distance.
-mudchicken
And to add to that I’ve been on an Amtrak Superliner while going through some crossovers… there’s a real bad one up by Kansas City, I was in the observation car upper level when we went through it, I thought for sure we would tip over! wow! A man comented how “they were trying to rock us to sleep!” The cars sway all the time, however, just watch it when going from one passenger car to the next, but don’t stay on the end platforms too long or the conductor will make you go find your seat.
I was surprised how smooth train travel was on my first Amtrak trip. Tourist lines generally run over uneven jointed rail, not the continous welded rail of the Class I’s. But when we go through some crossovers and switches a vibration can definatly be felt by my feet through the floor.
When I ride the Amtrak from KC to STL and those long UP coal trains zip by with the big and loud SD70M’s on front and rear just inches away from my window that’s enough to give me goosebumps.
Perhaps one reason is that weight distribution on the supporting ballast shifts each time the route is changed and traversed over. Weather may intensify it. On non-turnout segments, little weight distribution changes take place. To see 70 M.P.H. rather bouncy trains at turnouts is common. Track gangs will eventually get to it. If a train crew person does not look back in concern, I would not worry about it.
I’ve seen cars rock left and right, but only at like 30-40 MPH, on a straingt piece of track, no junctions. But its still scary[:0][:0], makes me step back a few feet.
Mudchicken gave you the answer, in a way.
He mentioned harmonic swaying.
If a railcar in a train sways, part of that motion is also transfered to the car ahead and behind, which in turn makes the car its attached to sway, so forth and so on, through the entire train.
Of course, as this motion is transferred from one car to another, some of the enegry is spent and negated by the suspension system, and the sway gets less the farther down the train it travels.
At high speeds, it isnt too noticable, as the suspension system in the cars are designed to react best at a certain rate, between 60 and 70 mph
Mudchicken can give you the correct or true speed, he has to design track to match the type of traffic/weight.
But at low speeds, around 15 to 20 mph, the suspension system cant react fast enough to dampen or cancel out the sway.
In fact, it can enhance the motion, to the point it balances the side to side motion almost perfectly, if the car tilts 5 degrees to the left, the suspension system will push it back just hard enough to make it sway or tilt 5 degrees to the right.
Because all the cars will pass over the same point on the track that causes the sway in the first place, a frog or a rise/ dip in one rail, they all get the same amount of “bump” to start the swaying.
Because they all share almost the same amount of sway, and each car contributes its enegry to the motion of the entire train, and to the car ahead or and behind, it can continue for quite some time, all the cars end up contrubuting the same amount of sway in harmony.
I have seen entire trains look like they were doing the “wave” you see sports fans doing at ball games.
Its a wild sight!
Due to the fact that all the cars are not exactlly the same, some loaded, some empty, different springs and construction, eventually the harmonic motion will be interupted, and the suspension system will slowly cancel it out.
One car wi
Track gangs will eventually get to it. If a train crew person does not look back in concern, I would not worry about it.
There is a old saying that goes something like this. if looking back would bother you seeing what the cars are doing, dont look. So as long as my brake pipe pressure is right and there is a reading on the rear from the eot. put the throttle in 8 and dont look back.
I recall hearing a story about two CNW trains passing each other on the double track main and smashing into each other. But that was not due to switches, but what you say makes sense. I have looked pretty closely at switches and have watched trains go over them, and boy do they sway!
Jermery,
It dosnt always have to be a switch or frog.
Any dip or rise in one of the rais can get it going.
Stay Frosty,
Ed
Jointed Rail Bad, CWR Good…
i thought the sway was due to the cars reacting to rail joints, not part of a turnout… when a car passed over a joint, the car might sway to that side…
the reason i thought the sway as due to rail joints was because there were long stretches w/o turnouts… this was before welded rail was common, which is how long it’s been since i trainwatched…
it impressed me that two adjoining freight cars never swayed together… same-side sway (good name for a rock band) alternated
with cars…
which brings another question… do european freight cars sway the same way as u.s. cars?
the wheel suspension’s different, the coupling’s way different…
the rails meet at the same place on both sides, like model rail… they did in the 60s, anyway…
Lotsa reasons why track has surface problems. CWR just gets rid of some of the more obvious headaches.
On the european car issue, ever seen the single bogey trucks under a TTOX flatcar ?- same thing. Damn things do not steer well at all and have issues with side sway at speed…
Do Austrailian cars sway the same way? Or do they go back-to-front instead of side-to-side… Maybe with the water circling different the cars sway different…
I keep hearing of the infamous TTOX cars. These turds are restricted in so many ways, I don’t know why they just don’t send them to the scrapper. Are there many of them still running around? Why a single axle truck?
Ken
Why? - Tare weight (i.e. more weight shipped with less fuel)
MC
Ahhhhhh, thanx, Mud
Ken
Hi Everyone
When I go railfanning I notice all the time that when the train passes over a switch it rocks back and forth quite alot,what causes this? and does it happen alot because it can get a little scary watching all those freight cars and loco’s sway back and forth.
thanks and I hope that somebody can answer this.
Jeremy
Hi Jermey,
I will give it a whirl.
Know what a track frog is?
Its the point where the two rails meet, a very heavy guide ways for the wheel flange to follow.
Because it is such a heavy and stouter piece of track work, and because of the way turnouts have to operate, the support under a frog is greater and more spread out than the support under the opposing rail.
Bet the train sways out, away from the center or other track first.
The frog has no “give” in it like the rail does, no ability to flex, its almost like a bump in the track.
If the track work leading up to and away from the frog isnt kept maintained well, the force of running over the frog shifts the weight of the cars and locomotive to the outside rail, which tends to have more flex.
Over time, the outside rail will begin to settle deeper into the ballest, and the problem becomes even more pronounced.
Imagine driving a car, and you run over a bump in the road, but the bump is only on one side, say the passenger side of the car.
The passenger side rises up, and the drivers side will sink down, due to the action of the suspension, springs and shock asorbers.
Same thing with the locomotive and cars, the swaying is the result of the suspension system trying to compensate for the bump, or high spot in the rail.
Sometimes it can get so bad you would swear the car is going to tip over!
Try having to stand inbetween two opposing trains on double main, both running over the frogs on their track, and watching the cars, it looks like they are going to smack into each other at times.
On second though, do not try that at all, I get paid to take that risk, you dont, and shouldnt
In fact, if you dont railroad for a living, I suggest you stay at least 50’ back from the track.
Cars have banged into each other that way.
Stay Frosty,
Ed