INDIA has one of the largest railway networks in the world, carrying nearly 20 million passengers a day. Passenger safety is a key priority for Indian Railways, and as part of its efforts to ensure continuous improvements in safety, the Research, Design and Standards Organisation (RDSO) of Indian Railways, has challenged the industry to develop an indigenous and cost-effective signalling system to optimise train safety.

HBL Power Systems has been engaged in the development of train protection systems for some time, and pioneered the domestically-developed Train Collision Avoidance System (TCAS) under the guidance of the RDSO.

As the name suggests, TCAS is a comprehensive train protection system which is designed to prevent head-on, rear-end and side-on collisions. In addition, TCAS offers a number of Automatic Train Protection (ATP) features such as Signal Passed at Danger (Spad) prevention, cab signalling and speed control. The system also has a manual SOS function, which can be activated either by the driver or the station supervisor. TCAS can detect and alert incidents of derailment, train splitting and rollbacks, and provides protection against collisions at level crossings.

While typical ATP features offered by systems such as ETCS rely on signalling information for prevention of accidents caused by driver error, TCAS uses not only signalling information but also train location data to provide an additional layer of security.

TCAS comprises three main sub-systems: Loco TCAS, which is the onboard equipment; Station TCAS which is deployed at stations and level crossings; and lastly RFID tags on the tracks.

The system uses radios, which operate in UHF frequency for communication between the onboard and stationary equipment. The communication range is designed to maintain safe braking distance in cases where there is a risk of an imminent collision, while each TCAS unit must be able to communicate with all other TCAS units within a 3000m radius.tcas

When the locomotive is within transmission range of the Station TCAS unit, the station equipment acts as the master and provides the movement authority to the locomotives. On longer block sections, when lineside equipment is not within communication range, onboard equipment exchanges data directly between trains to maintain the collision prevention function.

The Loco TCAS equipment comprises the central computer unit, power supply, radio unit, brake interface unit (which overrides the braking system of the locomotive in the event of an imminent collision), RFID reader, and driver-machine interface (DMI). The DMI (pictured) of TCAS has been designed as a user-friendly unit requiring minimal input from the driver during operation. The stationary equipment comprises the central computer, power supply, radio unit, field interface unit (which interfaces with the interlocking for signalling inputs), and station master interface (SMI).

The onboard equipment has a GSM interface, which is capable of interfacing with two different service providers to connect to the centralised management system. Loco TCAS can also switch between leading/single mode and coupled/banking mode to suit different operating requirements, and can be fitted to any locomotive, multiple unit or driving trailer operating on the Indian Railways network, including microprocessor-controlled units.

Both Loco and Station TCAS units are fitted with data recorders to log events with a date and time stamp, and all units can operate through a battery back-up in the event of a power failure.

While ETCS provides ATP functionalities, the primary objective of ETCS was to evolve common standards for interoperability to support international operations. Many of the interoperability features offered as a part of ETCS are not relevant for many non-European rail networks, as they do not operate beyond their national boundaries. This makes ETCS deployment a very expensive infrastructural investment especially for a country like India where the rail network is close to 70,000km with new lines being added every year.

When the development was initiated at HBL for the TCAS system, the design team was given four distinct requirements, which the system had to address. These included:

• inclusion of both ATP and collision prevention capability

• safe and reliable operation without degrading existing operational safety

• the ability to maintain or increase current levels of existing capacity utilisation, and

• offer significantly lower cost than ETCS.

The development of TCAS began in early 2010, and in 2012 the HBL design team delivered the system that met all four of these challenges.

Following the completion of laboratory simulation trials, HBL's system was put through real-time on-track tests near Tandur on the South Central Railway in Andhra Pradesh between September 25 and October 17 2012. Two TCAS-equipped locomotives ran a series of comprehensive trials to demonstrate the performance of the technology under a number of different scenarios, including head-on and rear-end collisions, excessive speed, Spads, and operation of cab signalling. Converging speeds of around 200km/h were used for head-on collision tests and just under 100km/h for Spad testing.

On October 16, the trials were witnessed by the chairman of Indian Railways Mr Vinay Mittal along with other senior railway officials, demonstrating the keen interest the leadership of Indian Railways has in the new safety system.

After witnessing the tests, Mittal said: "It's a groundbreaking technology and we would like to complete all the trials within a year. TCAS has more capabilities than technologies being used in many advanced countries".

The Additional Members panel of the Railway Board also also visited the test site for a demonstration of the system in November 2012. All the tests carried out during the Additional Members panel visit also were successful, paving the way to adopt TCAS as the primary safety system on the Indian Railways network.