Signalling on Indian Railways is based on the absolute block system, which permits only one train between two stations. Since this imposes restrictions on line capacity, automatic signalling is provided in suburban areas with signals every kilometre to run a larger number of trains. These systems depend entirely on the vigilance of the driver to sight the signals to run a train and are, therefore, prone to human error. The issue of adopting intelligent systems which alert the drivers about signals and route data ahead, and override their erroneous actions or inactions, has been under consideration for decades.

The signalling systems in developed countries have advanced to significantly-reduced human element. In Europe, since trains cross from one country to another, the European Train Control System (ETCS) for signalling and train control was developed and superimposed on the existing systems in the 1990s as a uniform interoperable system for all countries with standard gauge tracks.

Its first fully-developed version, ETCS-Level-1, has track-side radio balises, which transmit signal aspects and route data to a matching on-board receiver and the driver’s cab-signalling monitor at fixed points. The on-board computer controls the speed and braking from this data, overriding the driver if the target speed is exceeded. Because of the spot transmission of data, the train must pass a balise to obtain the next set of data.

The next version, ETCS-Level-2, is a GSMR/GPRS-based system which displays signal and route data in the cab through continuous exchange of information, including its position and direction, with a radio block centre (RBC), which also oversees and controls the train movement. Balises and other track-side equipment, and not cheaper alternatives, are still used as a reference positioning beacons for on-board equipment and to confirm train integrity as a legacy of upgrade from ETCS-Level-1.

ETCS-Level-3 is an untried futuristic system which obviates track-side equipment, with the RBC receiving data continuously and permitting the smallest possible distances between trains, with the train itself being a moving block. While line capacity goes up with ETCS-Level-2, ETCS-Level-3 would take it to a theoretical maximum.

The Railways has pursued modernising its signalling systems in dribs and drabs with systems like automatic warning system (AWS), a simple system for alerting drivers and auto-braking, and train protection and warning system (TPWS), which is roughly akin to ETCS-Level-1.

Electronic signalling

The first significant initiative was mooted by Konkan Railways in early 2000s with anti-collision device (ACD), an electronic non-signalling system, to eliminate collisions due to human errors. It has a network of onboard devices for cabs and guard-vans and track-side devices at stations/level crossings.

The devices along the route communicate with each other through radio in a radial range of 3 km. On board computers use GPS inputs to determine train location, speed and course of travel. The system was tried out on the NF Railway with moderate success, a hitch being nuisance overrides, causing slowdown of train operation. The bigger issue was that ACD was a black-box for the Railways, with the IPR resting with a lone vendor who was unwilling to share it with the Railways.

Around 2006, the Railways decided to develop multiple vendors of ACD renaming the systems as train collision avoidance system (TCAS). As the said vendor was not forthcoming to take it forward, some bold engineers of Research, Design and Standards Organization (RDSO) mooted a change in the philosophy, committing themselves to move far beyond an anti-collision system to develop a modern signalling system akin to ETCS-Level-2, with, among other things, distance-to-go signalling, prevention of collisions and signal passing at danger (SPAD), cab signalling, speed control, line-capacity friendliness and enhancement capabilities.

The rest, as they say, is history. In spite of stiff opposition from the champions of ETCS-Level-2 or the lower-grade ACD, these engineers worked steadfastly on TCAS between 2011 to 2016. The current status is that it has been proven on a long stretch on South Central Railway to be a versatile system, which would meet the needs of the Railways for decades to come.

The ballpark expenditure would be ₹40-50 lakh per route kilometre against ₹2 crore for ETCS-Level-2. To convey that the system is far more than the limited scope of anti-collision, it has been rightly named as Kavach.

This success needs to be celebrated as it has the promise to save thousands of crores for the country. The engineers who worked on the project should be applauded to propel others to emulate them in the field of railway engineering.

The writer is a retired General Manager, Indian Railways, and an independent consultant

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