FOLLOWING almost 30 years of development, JR East's Advanced Train Administration and Communication System (Atacs) was ready to enter commercial service by March last year. Final verifications had been carried out on the system which recognises train locations and uses cab signals rather than traditional ground equipment such as track circuits and wayside signals.

However, on March 11, disaster struck.

A huge earthquake and tsunami hit eastern Japan, leading to widespread destruction. Homes, cars, bridges, railways and roads were all swept away in seconds by the brute force of the tsunami, the enormity of which was captured in disturbing images that were beamed around the world.

Inevitably the Atacs system prepared by JR East also suffered damage. But despite some calls to abandon the project, the railway decided to push ahead, citing its capability to improve safety and reliability as well as reduce life-cycle costs.

JR East's faith in the concept was finally realised seven months later. On October 10 2011, commercial operation of Atacs began on the Senseki Line, an urban commuter line in the Sendai area, with all operating trains switching from conventional train control to the new system.

Atacs' functions are similar to European Train Control System (ETCS) Level 3 and communication-based train control (CBTC). The concept was initiated in the 1980s and its development, led by JR East, has mirrored the rapid expansion of digital radio and mobile telecommunication technologies.

Atacs' high level of safety is achieved by utilising train location recognition and train distance control technologies. For train location recognition, each train uses a tachometer generator to detect its own speed which it subsequently uses to calculate the distance it has travelled and consequently its precise location.

Train distance control is based on a moving block signalling system where each train continuously transmits this location information by radio to simplified ground facilities. Based on this information, the ground facilities set a Limit of Movement Authority (LMA) for a train at the point of the specified safety margin from the rear end of the preceding train. This means that the LMA of a following train is moved forward according to the movement of the preceding trains and any following train calculates its speed profile based on the LMA transmitted from the ground facilities, with the maximum authorised speed shown on the cab display. Whenever actual speed is greater than the maximum authorised speed, the train is slowed down automatically.

Atacs has the following complementary functions based on these core technologies to enhance safety and reliability:

• interlocking function: route control by computerised interlocking equipment is included in Atacs

• train protection function: emergency signals from level crossings and station platforms are transmitted by radio to trains allowing automatic braking, and

• fixed location speed limit function: speed checking and automatic brake control according to speed limits in fixed locations, such as curves and points, are registered in the on-board device.

The system also has functions for automatic emergency braking and train location information storage in situations where Atacs systems might be down. Moreover, Atacs will be equipped progressively with additional functions beginning this year including level crossing control, which utilises train location information, and temporary speed restrictions set by dispatchers. These functions will inevitably lead to improvements in safety due to the reduced risk of accidents at level crossings and the optimisation of the duration of alarms at level crossings and platforms.

Capacity is also be enhanced through shorter headways with the addition of moving blocks, while eliminating or reducing cables, signals and track circuits will result in less infrastructure work and reduced life-cycle costs. This particular element was reflected during the recovery from 2011's earthquake when Atacs suffered less overall damage than traditional systems due to their need for significantly more lineside equipment. Significantly reduced signalling infrastructure will also improve safety as there will be far fewer staff on the track.

Regional lines

Continuous improvements in efficiency across the railway network is an essential mission for all railways, and one of the notable merits of a radio-based train control system is simplification of ground facilities.

JR East's network spans 7500km across 70 lines, including 2300km of regional services on 33 lines. The important challenge on regional lines is enhancing safety and reliability without incurring any additional operating costs. Here, the simplification of ground facilities enabled by a radio-based train control system is important, and JR East is developing the Japan Radio Train Control system for Regional lines (JRTC-R) for these applications.

On regional lines, where only one train is allowed in a section between adjacent stations, LMA transmissions to preceding trains is only necessary in the sections around stations. JRTC-R prevents collisions by managing the identification of each train and the procedures for checking trains in and out as they arrive at and depart from stations.

One of Atacs main benefits is an increase in capacity. However, JR East concluded that this function could be eliminated when taking into account the characteristics and needs of regional lines. Radio controlled areas are required only in and around stations, making it possible to simplify the system structures further, reducing JRTC-R's life-cycle costs.

In addition to the merits described above, a radio-based train control system has the potential to enable breakthrough innovations in maintenance through integration with other systems, such as radio-based safety equipment for ground work and on-board monitoring systems.

JR East plans to continue developing and introducing radio-based train control systems depending on the characteristics and needs of its lines. Based on experiences from the pilot Senseki Line project, Atacs is likely to be introduced on lines with high transport volumes in the Tokyo metropolitan area, while JRTC-R will continue to be rolled out on regional lines.