Track
Continuous rail turnouts favour mainline track
Tests of a new continuous rail turnout concept, which was recently commissioned on a BNSF line in Texas, has the potential to reduce maintenance costs and improve safety, as David Davis, senior scientist and Rafael Jimenez, senior engineer at Transportation Technology Centre Inc, United States, explain.
L
IKE all of the Class I railways in the United States, BNSF’s network has thousands of
turnouts to diverging passing loops and service lines to industrial facilities which, while only carrying minimal traffic, are essential to its everyday operations.
Despite not being in regular use, each turnout requires around 20 times more maintenance than plain track because of the exposure of its vulnerable components to the forces of every passing train.
In an effort to increase the turnout service life as well as improve safety, BNSF, Progress Rail Services and Transportation Technology Centre Inc (TTCI) joined forces to develop a continuous rail turnout concept. As the name indicates, the key feature of the design is the continuous mainline rail through the switch and crossing which aims to improve the performance of the mainline side of the turnout at the expense of the capability of the diverging route. A prototype continuous mainline rail
turnout designed for low speed and low volume diverging traffic was evaluated under 39-tonne axleload traffic at TTCI’s Facility for Accelerated Service Testing (Fast), in Pueblo, Colorado in spring 2012 following a two-year development programme. The switch configuration of the new design (Figure 1) differs from a conventional turnout design (Figure 2) by having both fixed stock rails on the mainline route. The conventional switches have one fixed stock rail and one moveable switch point on each route with both routes having running surface discontinuities on one rail. As the train passes over the turnout, wheels transition from stock rail to switch point on one rail of each route with the moveable switch points both located on the diverging route. Note in Figure 1 that on the continuous mainline rail turnout, one switch point is located on the gauge side of the left stock rail, and the other switch point is located on the field side of the right stock rail.
Figure 1: the prototype continuous rail turnout has undergone extensive testing at Fast.
The continuous mainline rail turnout design is also referred to as a “vertical switch” because it functions by lifting wheels over the mainline rails, instead of providing a gap in the mainline rail for wheel flanges to pass through. This switch is similar to the lift frog design, which has been successfully implemented by North American freight railways. Like the lift frog, this design strongly favours the mainline in terms of ride quality and allowable speeds so is ideal for loops and industrial sidings accessed from the mainline.
Testing
Figure 2: comparative tests have also taken place on a conventional split switch turnout. IRJ May 2013
To evaluate the prototype design, the test team conducted a series of proof tests, consisting of mainline and diverging operations, track strength measurements, and running surface wear measurements. Mainline testing
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