Routinely, our local Virginia Railway Express trains get slow orders due to thermal expansion of continuously-welded rail, which the jargon defines as “sun kink.”
These trains can be reduced to 60% or less of their regular speed and the always informative VRE newsletter discusses it more than once during the summer months. It even gets into the traffic reports on our local station.
What I’d like to know is, why are there not any thermal expansion joints installed when a line installs continuously-welded rail? Is this the reason for “sun kink” and hot summertime slow orders? And if so, why do we tolerate slow orders due to “sun kink?”
As an aside, the VRE newsletter is a very frank and candid window to the operations of a transit public/private partnership. For example, they frankly tell riders that commuter rail does not make money, and freely point out to commuters that VRE’s fares only cover 50% of operating costs. You can read it at http://www.vre.org/.
If there were expansion joints, it would not be continuously welded rail any longer. It would be jointed rail. Jointed rail was laid with some thermal expansion capacity at the joints, whereas welded rail absorbs all the thermal expansion by restraining the rail, compressing the steel itself, and transmitting the forces to the ties, and from the ties to the ballast section. The entire idea of welded rail is to eliminate as many joints as possible. Heat orders are placed on very hot days when the ability of the track structure to absorb the thermal expansion becomes less assured.
You’re probably thinking, “So what?” The drawback to jointed rail is much higher maintenance costs, and much higher maintenance time required on the track, which translates to a much higher access cost to operate the commuter trains, reduced capacity to run trains (in order to make time for maintenance-of-way), reduced reliability of passenger service, etc. It’s an economic trade-off, and in this case the railroad (CSX) is accepting the cost X of “heat orders” (with the agreement of VRE) on hot days and the resultant loss of train capacity and schedule reliability on those days versus the cost 10X of jointed rail, not to mention going back 50 years, technologically and economically speaking. It would be like substituting a horse-and-buggy for your car to eliminate the irritation of having to put up with taking the car in every 90-180 days for an oil change.
I’m not sure what you mean by “tolerating” slow orders due to sun kinks. Kinks are a result of poor roadbed and tie condition. Not enough ballast, mud holes, and poor anchoring all contribute to the instability which results in kinks. It is a multi-faceted problem that requires spending large sums of money to repair. Essentially when you have summer heating the rail will grow and if you don’t have enough rock and anchors the ties will move as the rail expands because there is nothing to provide stability to the rail and/or the ties. When you get enough growth the rail is going to kick out.
You’ve got two very good and comprehensive answers above. To add just a little bit:
5 or 10 years ago CSX - which I understand is the line that VRE mostly runs on - had a couple of nasty derailments due to sun kinks. At least 1 of those CSX sun kink wrecks involved an Amtrak train in Florida (if I recall correctly), which was discussed extensively on this forum about 1 or 1-1/2 years ago. That particular one was caused more by improper maintenance practices - not tamping or allowing the track to “bed in” (my term) sufficiently before resuming full-speed traffic, etc., if I recall correctly - as opposed to overall poor track condition, such as ties, mud, ballast, etc. as mentioned above.
Having thus been “snake-bit”, the immediate reaction by CSX - the “band-aid” fix, if you will - was to impose the hot weather slow orders, which CSX was far more aggressive in doing than any other railroad, resulting in far more delays for VRE and Amtrak on CSX’s lines than anyplace else. I believe that comparison remains valid today - for example, I’m not aware that BNSF places any restrictions (or at least nowheres near as limiting as CSX) - on BNSF’s “TransCon” line across the southwestern US deserts, even though the temperatures there routinely exceed those to which CSX’s tracks are exposed.
My opinion - then and now - was that rash was primarily due to the underlying problem of poor or insufficient track maintenance in terms of money being spent and the resulting quality of track, and secondarily by insufficient training and/ or supervision of the maintenance-of-way crews that compounded the underlying track conditions by aggravating or mishandling the sun kink factors. I also recall a report regarding CSX’s official standard for the “neutral temperature” of the continuous welded rail (“CWR”), which struck me as being unusually low when compared to other railroads, esp. NS.&nb
CSX (VRE & MARC) operates in the MOST POLITICALLY CHARGED environment in the country - the Greater Washington DC metro area. Whenever a frog farts on the track there is a news report on radio and TV about it within the half hour. CSX and it’s legal staff take note of this.
Heat orders are issued when the anticipated high temperature will be 90 F or higher. The heat order, when issued, applies to track having a timetable maximum speed of 40 MPH or higher and reduces those maximum speeds by 10 MPH. Heat orders are in effect from 1300 to 1900 - through the hottest part of the day. Heat orders are NOT issued because there ARE Sun Kinks, they are issued as a preventive measure. Heat orders apply to ALL TRAINS, not just VRE.
The derailments that CSX has had with heat related track structure movement were where timetable speeds were restored after track work prematurely. Whenever the track structure is disturbed (tie & surfacing gangs, rail laying gangs), the initial train over the disturbed track is limited to 10 MPH, subsequent to the initial train further trains are limited to 25 MPH for a period of time to, as has been previously mentioned, “bed in” the track. Operation of trains settles the track structure to the point that ballast/tie work themselves into a sustainable configuration.
When Sun Kinks are discovered, then M of W personnel will physically cut out a segment of rail and either apply joint bars or re-weld the track joint. If joint bars are applied the track will have a speed restriction until such time as those joints are re-welded.
As a corollary, when temperatures dive, there is also stresses a
…Sun Kinks: Doesn’t the engineering community have the instruments currently that they could install strain gauges at periodic locations in known troubled heat / cold spots to give a better indea of looming trouble…?
If so…couldn’t engineering then establish “charts” of performance over time and temp and perhaps sneak up on trouble spots with slow orders and whatever else could be done.
What I was getting at was that is “sun kink” a normally accepted phenomenon or does it happen when the state of the track gets bad? Sounds like it is the latter combined with generally over-protective CSX policy due to past experience.
If I remember correctly, also, this year they did mention on the radio that the track was recently replaced and needed to ‘settle.’ They didn’t say that last year.
For what it’s worth, I never hear about speed restrcitions on MARC’s Penn Line which is AMTRAK. Those lucky commuters rival Metro-North in high speeds.
Sun kinks are an accepted phenomenon, they will occur more frequently when maintenance gets deferred on a line. Over the past 5 years, the RF&P S/D from Fredericksburg to Washington has received some of the most extensive maintenance of any sub division on CSX, including new welded rail and an extensive tie and surfacing program as well as installation of new Control Points and signaling changes not to mention eliminating the single track operation over the Quantico Creek bridge. Additional changes and enhancements for this line are being worked on.
A bit more info on sun kinks. As discussed, they are fairly common where you have wide temperature ranges, such as where you have cold winters and hot summers. While the railroad can install additional ballast, better condition ties and fasteners, and other items such as anchors, the rail will still expand. The hope is that the rail grows vertically instead of lengthwise.
Sunkinks are not limited to welded rail. Jointed rail can have them jsut as easily, especially since joints typically pump a bit leading to a less structurally contained track structure.
A final comment. The FRA in their welded rail rules (49 CFR Part 213) requires that railroads develop procedures to respond to wide ranging temperature changes by using slow orders, additional inspections, etc. The railroad industry has been testing many automated inspection systems at the AAR test track and better physical track designs, but kinks are still a problem that railroads have to respond to.
Well, not quite - perhaps you meant to post instead that “the rail may still expand”. In an ideal world - which is often achieved on the well-maintained lines - the ballast, ties, fasteners, and anchors, etc. would work together so well that the rail doesn’t move at all as it heats up. What happens to the rail is that it experiences thermally induced compression stress - it is pushing against itself, but not going anyplace. As an analogy, think of an isometric exercise where you push against a solid wall. If you do it perfectly, neither you nor any of your appendages move at all, but you can sure feel the load / pressure /stress in your hands, arms, and muscles. It’s the same with the rail. The trouble starts when the rail expands - then it starts to move longitudinally. That motion - often called “running” - can be fairly harmless if it is small in magnitude and remains in the same direction as the track. But if the movement starts to or wants to get large in magnitude, and then is or becomes constrained in both directions - such as by a grade crossing, a turnout (switch), bridge, or even the weight (mass) of the adjoining length of track - then the rail and track will take the “path of least resistance” to relieve that stress. In this context, the concern is that would be buckling into a sun kink at an (in)opportune location.
Next, technically, the rail will grow vertically when under such heat-induced stress, but only on a microscopic scale, per Poisson’s Ratio (typically around 0.3 for steel, I recall).
Well, Paul, my computer is next to a north window (with frosted panes). Perhaps I should be like Mookie and wear gloves for this. However, I suspect that that would be the equivalent of being “all thumbs.”
Fortunately, we’ve moved up to double-digit positive territory here. It’s warm enough to snow again.
Comment wasn’t so much about capacity but it was in response to the comment that the line that VRE uses happens to be getting the most maintenance attention in the entire CSX system.
If you’ve got a scanner, listen in during very cold weather. You’ll hear about lots of “broken rails”. Sometimes the rails pull so strongly that the anglebar bolts are sheared completely in half, and sometimes the anglebar itself will seperate at the holes. I’ve seen pull-aparts that the rails were 3" apart.
Where’s mudchicken? We need his expert advice here.