Subsequent to formation of South Western Railway in 2003 out of a population of 245 stations, 84 stations were still interlocked with mechanical signaling. All these stations have been gradually replaced with Panel Interlocking. At present there are 309 stations with PI/EI/RRI (Panel operation), Colour Light Signals, Motor Operated Points, Track Circuiting and Data Loggers, thereby enhancing safety in Train Operations and Increasing Section Capacity.
Interlocking is an arrangement between various Signaling Gears, Points, Level Crossing Gates etc. to ensure safety in train operations.
The era of interlocking began with mechanical Lever Frames And Semaphore Signals. These Mechanical Lever Frames are required to be operated physically by Points Man who had to operate several levers in a particular sequence to receive or dispatch a train. This activity was time consuming and used to cause detention to train movements. As the size of the yards increased, the size of the lever frames also increased, requiring more spacious cabins. It also required more maintenance efforts from the staff.
With the advent of Electro Mechanical Relays, these Lever Frames gave way to Relay Interlocking. This resulted in expeditious operations from a Panel, with enhanced safety.
Panel interlocking is normally provided for smaller yards, ensures that all the conditions required for safe passage of a train are complied with. As of now, 168 stations have been provided with Panel Interlocking in SWR.
With the increase in traffic, major yards and Junction stations required to be provided with more flexible arrangement which led to the development of Route Relay Interlocking (RRI). Accordingly, it has been provided at one station of SWR.
With the development of Microprocessors, computer based Electronic Interlocking System has been developed for controlling the various Signaling gears from a centralized panel/visual display unit. This system offers advantages e.g. ease in installation and maintenance, less space requirement, lesser time for initial installation of equipment and ease of alteration in case of yard remodeling. Hence, Electronic Interlocking has been provided at 133 stations over SWR as on March 2022.
The initial Mechanical Interlocking system was provided with Semaphore signals, wherein the position of the arm indicates the aspect of the signal. With advancement in Signal Interlocking systems, Semaphore signals were replaced with Multi Aspect Colour Light signals to increase the speed of trains. These signals were lit by electric bulbs with lens combination for a better visibility and reliability compared with that of semaphore signals. However, since these Signal bulbs are prone to fusing due to aging and voltage fluctuations, LED units for lighting signals were introduced. These LED signals have very high visibility as well as reliability. Hence LED signals are provided at all stations over SWR.
To ensure safe passage of trains between two stations, Block Instruments are provided. In the initial interlocking systems Token Block Instruments were provided wherein the driver of a train can enter the block section only if he is in possession of a token, delivered by the token block instrument. This token was physically picked up by the driver of a running train and handed over at the next station. At times, these tokens were not able to be picked up properly on run due to speed of train causing detention. They were also liable to be lost when dropped at stations. Such detentions were avoided with the introduction of Token less Block Instruments. Hence, Token-less block instruments have been provided at 302 SWR as of now.
Other Modern Signaling Equipment Provided:
1.Block Proving Axle counters (BPAC)
It is a safety equipment which monitors the movement of trains into the Block section between two adjacent stations. This device counts the train axles entering and leaving a Block section and controls the clearance of associated signals ensuring the safety in train operations. BPAC have been provided at 291 Block sections over South Western Railway.
It is a Microprocessor based system which logs selected the events i.e. Signal gear operations and train movements in a station yard. This system helps in monitoring the functioning of Signaling gears, analyzing failures and is useful in performing preventive maintenance thus enhancing the reliability of Signaling system. Data loggers are installed at 319 stations over South Western Railway and are networked to central locations at Hubli, Bangalore and Mysore as well as Railway Board.
3.Integrated Power Supply (IPS)
Integrated Power Supply is a comprehensive power supply system which provides complete power solutions with redundancy, from a single system to all Signaling circuits. Its function is to provide a stable and reliable AC and DC power supply to the Signaling installations which is very essential for their proper functioning. IPS have been provided at 315 stations over South Western Railway.
4.Safety at Level Crossing Gates
All the Level crossings Gates in station area and other important and busy locations in the section between stations are provided with signal interlocking to protect the road users. There are 391 interlocked LC gates in South Western Railway Road warning signals with Hooters have also been provided at all interlocked LC Gates.
All Manned Non-Interlocked Level Crossing gates have also been provided with communication arrangement with nearby station.
5.Second Distant Signal
Second Distant signal is provided at stations to give advance information to train drivers regarding the aspect of the First Stop Signal ahead. With Double Distant Signal, a driver gets information of the First Start Signal 2 Kms in advance. This increases the confidence level of the drivers and helps in increasing the average speed of trains thus enhancing section capacity. 30 stations and 24 LCs are provided with Double distant signals over SWR
6.Intermediate Block Signaling (IBS)
IBS have been provided to split a lengthy block section into two, thereby enhancing the section capacity. In South Western Railway 13 IBS have been provided.