Are there temps during the summer that are too hot to run trains over a system? If so why and if not, are there still issues that occur when running trains during high temps (100 or higher)? I always read about cold temps that can create problems for trains (brakes/air pressure etc.) and switches etc. but I’m curious if there are service interruptions with summer temps.
Welded rail can heat up and expand and on occasion create something called a sun kink in the rail.
Steel rails respond to changes in temperature - both high and low. As the temperature rises - rail will expand. As temperature drops - rail will contract.
CSX issues Heat Orders when temperatures are predicted into the high 80’s and higher, also when the temperature CHANGE between low and high is expected to be more and 30 degrees F. Train Messages implementing Heat Orders are authorized by MofW personnel.
Remember - the movement of trains across the track structure applies force to the track with each axle that passes over a given point - thus setting up a vibratory type action that will facilitate the release of any unrestrined forces through the track structure. The track structure is designed to control all those forces, however, …stuff happens.
I am curious what happens along the same segment of rail when one part of the rail is in a very cool tunnel and the other part is out in the hot sun (also vice versa). Do they ever have that scenario or has it never been an issue?
The track is laid so that the ‘reference length’ of the rail is measured relative to a so-called ‘neutral temperature’ which balances expansion and contraction over an expected range of temperatures.
One approach that can be taken for anticipated rail temperature outside this range is to cut a length of rail out at particular locations and weld in a longer or shorter piece, effectively ‘shifting’ the neutral temperature to a different range.
Okay, makes sense. So heat is really an issue, at times, for rail and such. Locomotives handle it fine for the most part. I would assume there are probably procedures in place via MoW to address fire hazards with brush along the system in high fire danger areas (wheel slippage causing sparks…)?
MC, any comments?
If rail temperature rises, the rail gets longer and if rail temperature falls, the rail gets shorter. This raises the question of how rail can get longer or shorter when it is a part of track. Where does the extra length go when rail gets longer? If the track were simply two rails spiked to ties and lying on a flat deck like a concrete road, the extra rail length caused by expansion would buckle the track into a serpentine form.
But track laid in ballast is somewhat restricted from buckling into a serpentine pattern. This is because the ballast and the ties form a connection to the subgrade and that connection resists the ballast/ties from moving side to side or even up and down. This prevents the rail from getting longer even though its temperature is rising.
But how can the rail not get longer as temperature rises? For this feat, the expansion of the rail is internalized within the rail. The rail acts like an extension coil spring. So if you take a single stick of rail and pull hard from each end, so as to stretch the rail; it will stretch. It stretches to get longer. If you can restrain the stick of rail side to side and up/down, and press on each end of it, it will get shorter. If you release the rail from either the stretched or compressed condition, it will relax and return to its original length. So it is exactly like an extension spring.
Rail Expansion table vs. Temperature Change
Put a balloon between two boards, suitably anchored. Fill the balloon with air. Where does the balloon expand? It can’t move the boards, so it expands out the sides.
Same with rail. If it can’t expand lengthwise, it will expand widthwise. It will try to expand lengthwise, but the track structure prevents it from doing so, until it doesn’t. That’s when you get sun kinks…
Yes, compressing to reduce the length of the rail makes the rail fatter in the cross section. And that type of steel will rebound when the compressing force is removed. For this to happen, all of the steel within the rail has to flow in order for it to change shape.
About ten years ago during a major heat wave, I was taking the Capitol Limited back to Pittsburgh. It was a slower trip than usual because we were following a freight train that was running slow due to heat issues. They announced that we were being restricted from passing it as they had assigned our crew to look out for brush fires caused by the leading freight. Once we got to Cumberland, we were released from our brush fire duty and took off, passing the slower freight just east of town. That was one of the more interesting announcements I’ve heard on a train (The time that the police had our train blocking a grade crossing and a MARC train blocking a second one to keep a police pursuit from getting on the other side of the tracks. I’ve wondered about the legality of that one. And the time we stopped outside of Harpers Ferry because of flash flood warnings. Somewhere I have a video of the heavy thunderstorm lashing the lounge car).
The means of controlling the expansion/contraction of the rail due to temperature is performed by the rail anchors (looks like a clip on the base of the rail) or the use of an elastic fastener system (many kinds, often looks like a pretzel clip connected to the tie plate and pressing down on the base of the rail).
The “neutral temperature” is determined by the historical range of temps over the years for a particular location. In the northern plains this can often be in the mid 80’s or low 90’s, where as in the desert it may be in the low 100’s. Every railroad sets their own policy based on the location and the type of track (wood ties vs concrete ties, etc.)
As a rule of thumb, based on some testing, you will not see rail temps getting much above about 135 or 140 degrees. It will typically be higher than ambient and rarely less than ambient temperature.
If a train starts a fire, it’s pretty much always from the exhaust of the engine. In areas where grassfires are common, a railroad may choose to install spark arrestors on the engine. However, overall, I believe it’s less of a problem with diesels than with steam, since steam involved an external fire burning coal or in the early days wood, which would cause sparks and embers to go up the stack.
While sparks from diesels, and from failed/damaged dybamic brake grids can and do cause fires, I would suspect the biggest cause is from the wheels. Not the wheels themselves, but from the use of the brakes. Not only during a service application, but more likely from sticking brakes or hand brakes left (partially or fully) applied.
Jeff
Having watched CWR laying here in Northeast Arkansas. I forgot the time of year, but would think it was a cooler part of the year. The laying operations included a series of “flame throwers” that heated the rail before laying and securing to ties. The reason being as the rail lay in wait, on the ground, the ambient temperature would have the length skewed away from the middle of normal. Don’t remember the number of “flame throwers”, but it looked like a hundred blow torches. All of these were under one large piece of equipment, possibly called a “Rail Heater”??? endmrw0621232333
You could see this done in some operations by the use of ‘firesnakes’ – lengths of rope soaked in accelerant, snugged up against the rail web, and lit. We’ve had discussions about them, and more modern alternatives to them, in some threads here.
The Germans, in the 1920s, were studying the physics of sun kink and hit on the nifty expedient of heating the rail “ohmically” with heavy electrical current. This assuredly lengthened the rail… but doing it quickly caused the track to buckle upward, in a bow, rather than laterally (there are pictures of the result!)
Physics - amazing how it works.
Besides firesnakes, wonder what the RR name was for the piece of equipment I described? Rail heater (as opposed to Switch heaters)?
The German method and bad results, reminds me of the “Sherman Bowties” in the Civil War. endmrw0622231315
Phyics: I love it, it’s everywhere. After all Fis-ex is phun.
And I would say it works, all the time. When or if fooled by the outcome, there is some factor that was not paid attention to and the surprised ensued. The laws of physics are just that, a law. They work all the time. They are not theories that is speculation and at the time the best explanation known.
As an aside, I taught HS Physics. Most of my students would go further into engineering. And several would obtain a PE license. I warned them: When on a job and you show up with authority and “knowledge”…Don’t ever disrespect the ole man that has supervised for 50 years what you are working on. He knows about things that were not in the text book and all the teaching you had. He has a degree in experience, a PhD at that. Hear him out and then consider what to do. Nobody knows everything, if they say they do, they are lying and don’t trust them. There have been a few PE engineers who did not follow this advice and ended up red faced. Some even got fired or transferred. endmrw0622231330