Virginia Railway Express
Commuter Weekly, June 15, 2004
Heat kinks form when overheated track expands and cannot be constrained by the cross ties and ballast.
Spring seemed too short this year, with summer-like heat settling over the region far too early. And with it came more than just the bother of having to rely on air conditioning much earlier than normal … As experienced VRE riders know, heat also can mean that “heat restrictions” are placed on trains, forcing them to run more slowly whenever temperatures swing widely or reach extremes during the day. By running more slowly, rail lines are less likely to buckle and engineers therefore have a far better chance of keeping the train’s operation safe and avoiding, at worst, a derailment caused by a buckled rail line.
Why are the tracks susceptible to buckling? Historically, all railroad rails were 39’ long and connected together with bars and bolts that had slightly elongated holes to allow for the expansion and contraction of the molecules in the steel. It was much like the massive expansion joints you see at either end of many highway bridges-giant teeth that open and close to accommodate the coolness of the night and the heat of the day. Absent that kind of pressure relief, buckling can occur in steel or concrete when internal temperatures soar past 100 to 130 degrees.
Those joints were the reason for the “clickety-clack” sound of yesteryear, and although it was a romantic sound to many, it proved extremely troublesome for upkeep. The vibration of the joints created settlement and “pumping” of the ground underneath. This required frequent tamping and surfacing of the track as axle loads became heavier. The solution to that problem was welded rail-creating a smooth surface with no joints and less maintenance. The drawback, of course, was that without joints, there was no room for heat expansion and, thus, heat kinks!
To overcome the tendency of welded rail to “run” and consequently kink, railroads apply anchors at each cross tie to keep the molecules in check, and the track structure in line. “Running” (or compression) can result from both high ambient temperature, and from heavy freight trains applying the brakes consistently in one direction (such as going in a siding with a slower allowable speed).
Normally, these stresses are contained by the ability of both the railroad spikes and cross ties, supported by the ballast, (the stone under the rail and cross ties) to resist the side-to-side movement that causes buckling in the rails. A substantial ballast shoulder at the edge of the ties, and a “full crib” between the ties, are extremely important in overcoming the lateral forces. Specifically, railroads have applied anchors at most cross ties to keep the rail in check, and thus the track structure in line. However, in some cases these measures cannot hold the extreme amount of force that high temperatures can create. A sudden release of these stresses may occur, resulting in the rapid (and often audible) development of a “kink,” or sideways movement in the track.
That is where the heat inspectors come in. To add an extra measure of safety, track inspectors are sent out when the temperature rises quickly from night to day or when the daytime temperatures become extreme and the rail attempts to rapidly expand. These inspectors look for signs the track is in extreme compression and in danger of kinking out to the side. Signs include wrinkles in the track and disturbances of the ballast. If warranted by the inspection, speeds are lowered for freight trains, whose heavy weight can set the steel molecules in motion. Additionally, as an added safety measure, passenger train speeds are lowered, as well, and VRE must abide by those limits.
When a “kink” or severely compressed track is found, the track is taken out of service, the repair made, and then the track is tested and put back in service. That is why there are times that we are limited to one track during the summer as repairs are made.
So yes, train rides can take longer when heat restrictions are in place, but rest assured that these protocols and procedures are designed to get you home safely.