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How does the rail interlocking system work?

(Source: The Hindu; 11.06.2023)

What is the context?

Following the devastating train crash in Odisha’s Balasore district, where two express trains and a goods train were involved, investigations have turned their attention to the electronic track management system used by the railways. This tragic incident resulted in the loss of 275 lives and left over 1,000 passengers injured. The electronic track management system, which controls various aspects of train movement and track configurations, has become the primary focus of the investigations.

Introduction to Interlocking Systems

  • Interlocking systems are crucial components of railway signalling that help control and manage train traffic.
  • These systems consist of apparatus positioned along the tracks, which coordinate the movement of trains and ensure safe configurations at stations and junctions.
  • Their primary purpose is to prevent conflicting movements by allowing a train to proceed only when its route is set, locked, and confirmed as safe.

Electronic Interlocking Systems

  • Electronic interlocking (EI) represents an advanced form of signalling that utilizes computer-based systems and electronic components to control signals and points.
  • The Indian Railways defines EI as a “microprocessor-based interlocking equipment” capable of reading yard and panel inputs, processing them in a fail-safe manner, and generating the required output. In an EI system, interlocking logic is managed through software and electronic components, unlike traditional relay interlocking systems.

Implementation and Coverage

In India, the adoption of electronic interlocking systems has been significant. As of last year, approximately 45.5% of the Indian Railways network, comprising 2,888 stations, had been equipped with electronic interlocking systems.

Components of Electronic Interlocking Systems

Electronic interlocking systems consist of three essential components:

  1. Signal: Signals are light-based indicators that communicate the status of the track ahead to train operators. These signals display three different aspects: red (stop), green (proceed), and yellow (exercise caution), enabling trains to adjust their speed and movement accordingly.
  2. Point: Points are movable sections of a track that allow trains to switch between different lines. They guide the wheels towards a straight or diverging line. Switches control these movable sections, and they activate and lock them in advance to ensure a smooth and safe transition between tracks. Point machines are used to securely lock the point switches.
  3. Track Circuit: Railway authorities install track circuits along the tracks to detect the presence of a train. These track circuits are electrical circuits. These circuits verify whether it is safe for a train to proceed over a particular section of track. By detecting the presence or absence of trains, track circuits contribute to maintaining safe distances between trains and prevent potential collisions.

In summary, electronic interlocking systems play a vital role in managing railway traffic. By utilizing advanced computer-based technologies and electronic components, these systems ensure safe train movements and track configurations. Key components such as signals, points, and track circuits contribute to the overall effectiveness and safety of electronic interlocking systems.

Working Principle of Electronic Interlocking System

  • Determining Signal to Pass: The electronic interlocking (EI) system operates based on two crucial information points. The authorities consider two factors to determine whether to give a signal for a train to pass: the direction in which they set the track and the absence of any obstructions on the divergent track.
  • Aligning the Route and Locking Points: Once the authorities determine the route, they align it accordingly, and subsequently, they lock the points in a specific position. The train receives a signal indicating whether it should continue straight or switch to a new track. If the train needs to switch tracks, the EI system directs it to the empty track where the two lines meet. To ensure safety, circuits prevent other trains from entering that particular block. The authorities keep the points locked until the train crosses the designated section of the track, or alternatively, they withdraw the signal to proceed.
  • Indicating Clear and Safe Routes: If there is an issue, a red light flashes, indicating that the route ahead is not clear or safe for the train.
  • Data Logging for Record Keeping: Similar to aircraft’s black box, the signalling system records activities in a “data logger” storing information about the electronic interlocking system’s functioning.

Factors Leading to the Odisha Crash

  • Suspected Signalling Failure: According to The Hindu’s reports, people believed that a signaling failure caused the Odisha crash. Authorities initially granted the Coromandel Express, from Kolkata to Chennai, a green signal to enter the Up Main Line. However, they later took off the signal.
  • Deviation from the Intended Track: Coromandel Express, without a scheduled stop, diverted to the loop line near Bahanaga Bazar station from the main track. Unfortunately, the Coromandel Express collided with a parked freight train carrying iron ore, resulting in a multi-train collision.
    • Railway operators typically use the loop line as a side track to accommodate goods trains.
  • Impact of the Crash: During the crash, the Coromandel Express was traveling at a speed of 128 kmph (80 mph). The impact was severe. The Coromandel Express engine and initial coaches derailed, toppled, and collided with the last two coaches of the Yeshwantpur-Howrah train. The Yeshwantpur-Howrah train was running at a speed of 126 kmph.
  • Uncertainty Regarding the Signal: The authorities’ signal decision remains unclear. The authorities lock the points until the train crosses the designated track section or withdraw the signal to proceed.
  • Possible Interference with the Electronic Interlocking (EI) System: Railway officials suspect tampering with the “error-proof” and “fail-safe” electronic interlocking system. Despite its reliability, the system could potentially be vulnerable to interference or sabotage.
  • Fail-Safe Nature of the EI System: The designers made the electronic interlocking system fail-safe. In case of failure, all signals turn red, halting train operations. However there is always a small possibility of failure, although it is highly unlikely.
  • Driver Cleared of Responsibility: The authorities have cleared the driver of the Coromandel Express of any responsibility for the crash. Officials confirmed that the driver was within the speed limit and had not violated any signals.

Overview of India’s Railway Track System

  • Length and Scale of the Railway Network: The Indian Railways has the world’s fourth largest railway network, managed under a single authority. People often refer to it as the “lifeline of the nation.”
    • With an average of approximately eight billion passengers annually, the network spans an extensive distance of 68,000 km.
    • This vast network comprises over 7,000 stations, and the running track measures 1,02,831 km.
    • Taking into account sidings, yards, and crossings, the total track length stands at 1,28,305 km as of March 31, 2022.
  • Transition to Digital Technologies: Indian Railways shifted to digital tech, moving away from outdated mechanical systems in recent years. This transformation aims to improve safety and operational efficiency across the railway network. One notable advancement is the implementation of electronic interlocking (EI) signalling systems.
  • Expansion of Electronic Interlocking Systems: The Ministry of Railways has made significant progress in deploying electronic interlocking systems.
    • By December 2022, Indian Railways equipped 2,888 stations with EI, over 45% of the network. In 2022-23, 538 more stations were outfitted, surpassing the previous year’s 421.
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