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BNSF-UP Cajon Pass-Hesperia Good News!
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Willy: Excellent question. The longitudinal force of braking is transmitted into the track structure, and the track structure must transmit it to the ground. It requires a good track struture to do this every day under heavy load, and not fail. Where you'll see it fail is that the alignment on curves will try to creep outward, gauge will try to widen in curves, and the rail will try to creep downhill. If any of these are allowed to progress too far, there will be accelerated wear rates of rail, ties, and fasteners, and alignment will begin to change from what it should be. If those progress too far, there will eventually be a failure of the track underneath a train, and the train will derail. The solution is to pay close attention to the track, and that's what railroads do. All major routes, including this, are inspected visually at least once daily, if not twice to three times daily, and conditions that will eventually cause problems are noted at once, and decisions are made to shorten maintenance intervals, change track materials, or resolve the problem in some way. <br /> <br />In high-wear situations, railroads will upgrade track materials to something tougher. In areas prone to wide-gauge, such as sharp curves with large longitudinal and lateral forces, railroads will install concrete ties in place of wood, or in places where concrete ties won't work, they'll go to a resilient fastening system such as Pandrol clips instead of traditional cut spikes. Bigger and tougher rail is installed in high-wear situations. More attention is paid to a proper rail-head profile and removal of surface defects, through rail grinding. (Surface defects such as corrugation create impact loads which are transmitted into the subgrade and can cause subgrade failures and undesirable alignment variations.) More attention is paid to ballast cleaning, tamping, and maintaining track geometry. Track geometry is actually a very sophisticated science, and changes that are invisible to the casual onlooker have major effects, such as where the spiral into a curve begins; the length of the spiral and where it begins in relation to the superelevation; the form of the spiral; whether the outside rail is elevated or the inside rail depressed, and how much, and where; the exact gauge that is set -- sometimes it's widened slightly; etc. Software in tampers and other track machinery is set to obtain the proper track geometry for the particular situation. <br /> <br />The biggest influence of all is drainage: the three most important things in track are #1 drainage, #2 drainage, and #3 drainage. Improper drainage will destroy track alignment and material very quickly, and the speed limit must be lowered to keep trains on the track. All the concrete ties, clean crushed granite ballast, and 141-lb. rail in the world are worthless on top of a poorly drained subgrade. <br /> <br />Maintenance intervals will vary greatly based on tonnage, track materials in place, climate, and other independent variables such as the availability of track time, men, machines, money, etc. Each railroad sets it accordingly, and a great deal of the management time is spent deciding which is the most cost-effective solution. <br /> <br />OS
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