TTC OPERATED BY ENSCO
Replicating Real-Life Scenarios to Assess Track Service Interruption Detection Technologies Ground-truth testing of events that can lead to service interruptions Sean Woods, Senior Rail Research Engineer, ENSCO, Inc., Pueblo, CO Dave Mauger, Director of Innovation-Mechanical, CSX Transportation, Inc., Jacksonville, FL Jeff Fries, System Architect, Alstom, Grain Valley, MO Ashish Jain, Chief Technology Officer, Sensonic, Princeton, NJ
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ervice interruption of a mainline track may occur due to various events, including treefall, rock falls, washouts, or derailed rail vehicles. There is a need for technology to aid the railway in identifying these events and making appropriate responses to avoid safety risks and ensure minimal impact to operations. A challenge with detecting these events is that they can occur almost anywhere on a mainline. This requires the need for widely distributed detection of these types of events to ensure they are not missed. This project included a consortium of organizations led by CSX. Alstom and Sensonic served as the technology providers and the TTC facilitated on-track testing at its facility. Two detection technologies were investigated: Distributed Acoustic Sensing and Track Circuit Detection. Distributed Acoustic Sensing Fiber Optic Sensing based Distributed Acoustic Sensing (DAS) is a technology that relies on fiber optic cable buried alongside the track. Often these fiber optic cables are installed and already available for telecommunication purposes unrelated to DAS. However, these cables can also be utilized for detecting vibrations near or from the track. An optical interrogator is connected to one end of the fiber optic cable, and laser light is rapidly pulsed down the fiber. As the
4 Railway Track & Structures // July 2024
Figure 1. Test setup to replicate a tree falling on track.
light travels the length of the fiber, minute imperfections in the strand reflect light back to the interrogator – a phenomenon known as Rayleigh backscatter. Each pulse of light captures a snapshot of imperfections in the fiber. By rapidly pulsing light down the fiber and comparing successive sets of reflections, the interrogator can measure distortions in the fiber, indicating the strain and vibration the cable is experiencing. The result is a capability that can detect and measure vibrations occurring on or near the track along with their location and characteristics. This vibration-based sensing can be used to detect and monitor various events and changes along the rail network without specialized on-board or on-track equipment. Examples of applications of DAS include security monitoring, natural hazards monitoring, train tracking, and track condition monitoring. One optical interrogator can monitor as much as 60 miles of fiber cable along the rail track alignment.
Track Circuit Detection Traditionally, track circuits have been used to detect trains, broken rails and to communicate signal aspects. Track circuits apply an electrical signal between the rails and rely on passing rolling stock to shunt the circuit to prevent the transmitted signal from reaching the receiving end to indicate the signal block is occupied. However, in the absence of shunting, some current flows through the rails and into the ground. The amount of current flow is characteristic of a given signal block and varies with conditions such as ballast quality, soil moisture level and other aspects of the track structure. By precisely monitoring how much current makes it from one end of the block to the other, changes in the electrical coupling caused by track activity can be identified. Both Fiber Optic DAS and track signal-based detection systems can detect various events occurring on or near the track. However, both methodologies need ground-truth testing to rtands.com