Heat Restrictions FAQ
What Is a Heat Order?
It is an order given to railroad engineers to reduce their speed over a given section of track. Just as drivers are warned to slow down in inclement weather, trains are subject to the same thing, all in the name of safety.
The engineering staff imposes a heat restriction when the temperature of the air reaches a specific temperature or if it has been hot for a consecutive number of days. The slow-order instructs train operators to limit the maximum speed to 30 mph within the affected territory. The temperatures at which heat restrictions are imposed vary depending upon track characteristics. This has been MBTA policy for several years, and it is reviewed and approved by the Federal Railroad Administration (FRA). While the MBTA and Keolis Commuter Services realize the delays caused by heat restrictions are incredibly inconvenient, the safety of our passengers, employees and the general public is of the utmost importance.
Why Is a Heat Order Necessary?
The Worcester Line tracks consists in part of continuously welded rail (CWR) made up of welded sections, each ¼-mile long. When installed, the ends of these rail strings are welded together to create a seamless piece of rail that are free of joints, creating a smooth surface for trains and a smoother ride for passengers.
One challenge with steel rail is that when the temperature rises, the steel expands. When the temperature falls, the steel contracts. In fact, a 1,450-foot long section of unrestrained rail will expand nearly 6 inches when the temperature increases by 50 degrees. To counteract the expansion and contraction of the rail, several measures are taken to limit the movement in the track. Those measures may include heating the rail to “de-stress” it, anchoring the rail to the ties, and having sufficient stone ballast and wood (or concrete) ties.
With all of this holding down the steel rail, a compressive force builds within the track structure and rail. In extreme heat, the compressive force in the rail can build to the point that the track buckles under its own pressure, causing the track to shift suddenly. This sudden shift of the track is referred to as a heat kink, which often happens under the vibration and dynamics of a passing train. Heat kinks can cause harsh shifts in track, which can lead to derailments. To safeguard against heat kinks, a heat restriction is placed on the line.
Why does it seem the Worcester/Framingham line is the only commuter rail line under a heat restriction?
In the case of the Worcester Line, the track was built and maintained by previous railroads, which had different design and maintenance standards than the MBTA. And when the MBTA took control of the rail line in 2012, there were no heat records available about the original installation of the rail, which helps engineers decide if the rail is safe from heat kinks.
To compensate for these unknowns, over the past two years the MBTA has either replaced rail or de-stressed sections of rail to make the Worcester Line safer. That work is ongoing and takes time.
What’s the solution?
Recently, the MBTA awarded an “Early Action” rail de-stressing contract for 7.5 miles on the Worcester/Framingham line, and work is scheduled to start at the end of July 2014. However, the heat restrictions will likely stay in place during warm temperatures. The MBTA is also in process of procuring 80,000 linear feet of rail and will begin work to replace the rest of the old on the Worcester/Framingham line starting next April 2015. De-stressing section of the line will then continue through the 2016 construction season. When that work is complete, Worcester/Framingham passengers will hopefully be freed from heat-related delays.