Would limiting train speed across diamonds reduce the frequency of repairs?

[junior yardmaster]

I was watching a UP train running no more than 25 miles per hour across the Rochelle IL diamond, and it seemed to me that it was easier on the crossing at that speed than a train running 55 mph; the noise as each car crossed the diamond was pounding the crossing much easier.  Comments as to whether you think that limiting the speed across diamonds would reduce the cost and frequency of repairs?

[traisessive1]

They already are limited. 

[tomikawaTT]

Was the UP train loaded?  Or were you looking at a ferry run of empties?

Train speed isn't the only determining factor in rail pounding at specialwork.  It probably isn't even the most important.

Chuck

[daveklepper]

But despite all that the answer is YES.  How much may be debatable and clearly depends on lots of factors.

[mudchicken]

The impact speed is one of the few variables you have any control over. You can't do much about the weight or where the contact patch getting the beatdown is. Every little bit helps when you're stuck with an at-grade crossing and a limited number of options.

[dehusman]

Just looking at couple timetables it looks like most crossing diamonds are listed at 30-40 mph on 50-60 mph subdiv's.

[ChuckCobleigh]

35 mph through the Rochelle diamonds.

[tree68]

I recall reading in Popular Science (or was it Mechanic's Illustrated? - Dad got both) about an experiment on Daytona Beach years ago (but easily replicated today) in which cars were driven on the wet sand at a slow speed and at a high speed. The slow speed car left a definite imprint, the high speed not nearly as much.

Moving that to the railroad side of things, it would seem like a higher speed would lead to less vertical moment force.  Unfortunately, that same higher speed would also lead to a higher horizontal moment force, with the two combining at a vector angle.  Depending on the gap, that could be substantial - ie, the wider the gap, the more the force. 

That would put substantial impact force on the "far side" of the gap as speeds rose.

I would imagine that the angle of the crossing would have an effect, as well, depending on the gap created.  Would a more acute crossing offer better support to the wheels, lessening the impact?  Or would it be worse?

[Euclid]

tree68

 

I would imagine that the angle of the crossing would have an effect, as well, depending on the gap created.  Would a more acute crossing offer better support to the wheels, lessening the impact?  Or would it be worse?

 

I have always concluded that 90 degree crossing has the highest impact, and the impact becomes less as the crossing angle drops.  With a shallow angle, part of the wheel is already across the gap and picking up support before the rest of the wheel has loses its support from the first side of the gap. 

[Wizlish]

tree68

Moving that to the railroad side of things, it would seem like a higher speed would lead to less vertical moment force. Unfortunately, that same higher speed would also lead to a higher horizontal moment force, with the two combining at a vector angle. Depending on the gap, that could be substantial - ie, the wider the gap, the more the force. That would put substantial impact force on the "far side" of the gap as speeds rose. I would imagine that the angle of the crossing would have an effect, as well, depending on the gap created. Would a more acute crossing offer better support to the wheels, lessening the impact? Or would it be worse?

I thought the general consensus was that acute angles produced more impact rather than less -- there is a much longer gap across the whole effective width of the railhead when the angle is 'steeper' and you cannot have flange bearing.  What may be 'easier' is the peak magnitude of the shock at the other side, as the contact patch does not have to hit and surmount what is essentially a transverse edge, like that on a flat wheel, all at once...

I think it needs to be remembered that part of the 'hammering' is not limited by the acceleration due to gravity -- the springs in the truck will provide some accelerative force too.  I suspect this is a significant part of why the hammering is as violent as it is, especially if the peak of the downward acceleration is reached just at the point you 'hit' the rail on the other side of the gap.

I still think part of a solution involves cushioned panels in the diamond flangeways that do flange bearing long enough for shock mitigation -- unlikely as that is to be developed in the USA for a variety of valid railroaders' reasons.

[Paul of Covington]

   Until we had a discussion here on owls diamonds and jump frogs a few years ago, I had assumed that all frogs supported the wheel flanges.   I probably got that impression from observing streetcar tracks.    Why aren't frogs designed that way?   I realize that flange height varies with wheel-wear, but if the frog is designed to support something near the shallowest flange, and the flange support is designed with a gradual ramp, the pounding would be minimized.   There must be a reason I haven't thought of.

[mudchicken]

Tradeoffs: As you below a 45 degree angle, your frog structure gets narrower and the point gets more brittle because it is less massive and takes on bigger parts of the load transfer over the gap.

OWLS frogs, by their nature are slower on the raised side and have to be tangent to avoid lateral thrust while passing over the tops of the opposing rails w/o any guidance. With worn wheels, that problem only gets worse (Sorry - have a problem with some of the mechanical guys and their AAR gages saying nothing is wrong with the wheel when the flange has an edge that's sharp to the touch. That baloney will set most roadmasters off like a roman candle.)

For places where you have curve frog geometry, the thing is aready laid flat and with no superelevation in the curve, of course your track speed is going to be slower to handle the centripital forces.

As far as why all frog flangeway channels don't support the wheel flange. FRA 49CFR213.137(a) is there for a damned good reason. INDUCED WHEEL CLIMB IS NOT TOLERATED and wheel flange impact nicks are also a capital bozo no-no. OWLS frogs have extra scrutiny because of the FRA exemption, and crossing frogs already are extra over-inspected because they are the most brittle, most expensive part of the track structure.

(Don't you dare run-in the slack going over an OWLS frog.)

[Euclid]

With a 90 degree crossing, the wheels encounter an open gap of about 1.5 inches or more.  It is just like a rail joint with the rails pulled apart leaving the gap.  The wheel loses all of its support as it leaves one rail, and does not recover any support until striking the rail on the far side of the gap. 

With a crossing at a shallow angle of say 30 degrees, wheel is actually supported all the way across the gap.  As one side of the wheel runs off of the rail head, the other side is running onto it.  So in effect, there is no gap to cross. 

However, the total contact area between the rail head and wheel tread is reduced during the crossing since part of the wheel tread is over the gap.  The reduced contact increases the loading per square inch, and this increases the wear of the rail head near the flangeway.  As the rail heads wear down, they create a dip in the support.  As wheels drop into that slight dip, they impact at the bottom of the dip as they begin to climb out of it.  That is the impact that you hear.  It is not directly caused by the gap (as it would be with a 90 degree crossing). 

This impact is upon a relatively small portion of rail head surface, thus accelerating the wear.  As you can see, part of the impact falls only on a sharp point of rail.

Here is a good explanatory video:

https://www.youtube.com/watch?v=MbSmoUH1Cqk

 

The video does also mention modeling practice of including a plastic bed continuous through the frog to provide supplementary flange bearing support.  Theoretically, this flange bearing could also be done with prototype railroad practice, but it is not, as is explained by Mudchicken above.

[cefinkjr]

junior yardmaster

Comments as to whether you think that limiting the speed across diamonds would reduce the cost and frequency of repairs?

Yes, but ... There is always the cost of reducing costs.  In other words, reducing the cost and frequency of repairs by limiting speed is bound to raise some other costs.  I'm not prepared to even guess what those might be; I'm just playing devil's advocate.

On this general topic though, I distinctly recall seeing moving frog switches years ago.  The frog didn't really move; it was the closure or wing rails that actually did the moving in synch with the points so that there was no gap between the end of the closure rail and the frog.  The wheel was supported throughout just as it would be on any other piece of track.

These were very high speed switches (usually at both ends of a very long crossover); they seldom required any reduction for even the fastest trains.  I don't know for sure but I'd guess that the installation cost of these was very high; probably twice the cost of a normal switch.  Operational cost would have been only a bit higher but maintenance costs OF THE FROG would not have been too high.

Does anyone know of any of these currently in service?  And, more importantly to this thread, were there or are there any crossings with "moving frogs"? 

[BaltACD]

High speed switch with movable point frog.

 

[daveklepper]

Metro North has such switches between Mount Vernon and White Plains, rode over them before leaving in 1996.   I am sure there must be many on the NEC.  But you often still need a speed reduction, say from 125 mph to 90 mph or so.  Remember, you cannot have super-elevation as on a normal curve for a crossover between tracks on a double-track line.

And flange-bearing switches are standard for streetcars, especially for in-pavement sharp-turn switches.

There are also diamonds with movable wing rails, and then there are the Owl Diamonds with on route high-speed with continous rail and the other low-speed with the gaps for the high-speed rout's flanges.

[mudchicken]

Somebody may be confusing spring frogs with movable point frogs which really appeared in this country after the late 1980's after Britain's Henry Boot Co. re-engineered the things into something more reliable. Spring frogs have had an on-again off again relationship in this country due to adjustment issues caused by the horn springs failing.

Moveable point frogs are common as corn in Iowa along the western transcons. JeffH's railroad also has little signs announcing to the world what they are. (so they don't get run through like their switch point cousins ... and ruin the switch machines)

[switch7frg]

Fasinating post on dynamics and geometry. That explains the reason why boiler shoes let the boiler move back and forth in the days of steam. The other event on the diamond was the crushing  of the ballast as the train cross over. some times the dust and rock bits flew.

[BaltACD]

MC -

Maybe you can answer.  Why are switch machines constructed so that the whole assembly needs to be replaced when the switch gets run through, rather than just a easily replaceable $10 part?   I am not intimating that running through a power switch is a inconsequential act - it is not; but having the switch spiked and out of service until a replacement switch machine can be secured and installed seems like too severe a penalty on operational efficiency.

[mudchicken]

Balt: You're kinda in the same boat here. The track side often grumbles about the signal side "gold plating - new" everything they do. That being said, we all know about the game of mechanical advantage, reliability, uniform interchangability and performance. The design on the GRS "torpedo tubes" and the USS switch "box" machines is hardly new. They do their jobs admirably and are inspected to death by the signal maintainers (dc electric ground monkeys) ....but the insides of those rascals make a Swiss watchmaker proud. The new hydraulic machines are neanderthal in comparison, in a technical way (they are still evolving).... 

[Deggesty]

  à Amazing Antique Desk

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[switch7frg]

Johnny, that desk is truly fantastic. The folks that designed it really had a brilliant mind. I would guess it is priceless to say the least.