International Railway Journal - October 2008 - (Page 33) y forward track circuits and lineside signalling, we will be able to eliminate malfunctions arising from such equipment, and by using moving block signalling, train frequency can be increased. The second objective is to improve safety. By controlling the speed pattern of trains, we can prevent them from exceeding their speed limits. In addition, if a barrier is not properly functioning at a level crossing, ATACS will force the train to come to a stand before reaching it, improving safety for road users and train passengers alike. The third objective is cost reduction. As well as reduced maintenance costs, the high initial investment needed for such lineside equipment is eliminated. We expect the system will require less labour when installing it. Crucially, ATACS is different from ERTMS Level 3 in that it can control the interlockings and the level crossing by two-way radio communication. ATACS’ train control method is fundamentally different from conventional signalling, because train position detection is determined by onboard equipment rather than track circuits. Information transmission between the ground and the trains is conducted via digital radio communication, and the signal is displayed in the cab. There are a number of advantages of using radio as a means of communication. First, the use of radio increases the amount of information which can be transmitted, and more detailed information between lineside and onboard equipment can be communicated. While continuously obtaining train position from lineside equipment, onboard equipment can calculate and analyse train position and its speed pattern. We can free ourselves from conventional methods of information transmission using track circuits, meaning that with ATACS we can take advantage of commonly used information processing technology, making it easier to introduce state-ofthe-art technology. Finally, the current signalling system is based on unilateral one-way transmission of information from lineside to onboard equipment. With ATACS, train control using bilateral twoway flow of information is possible, allowing trains to transmit and feedback information such as monitoring abnormalities on the tracks or status of level crossings. In ATACS, train spacing is controlled by a speed-check pattern calculated using information on each train’s limit of movement authority, speed limit, and track gradient. Individual trains determine their location by calculating running distance using a tachometer generator, and by checking ID beacons on the ground. This positioning information is then transmitted by radio, and with error detection, the system retains a frame rate of 99.9%. There is also an automatic hand-over function which ensures uninterrupted transmission when a train changes its radio frequency between two wireless base stations. Thus, instead of relying on track circuit data, the locations of all trains are continuously updated by radio transmissions sent every 960ms by individual trains. With this information, lineside equipment can manage all trains, and confirm their locations when we perform lineside equipment maintenance and restoration. The logic of interlocking control in stations is the same as the conventional system. However, the location of the front and rear end of trains is determined not by track circuit but by creating a ‘virtual block’ representing the space a train occupies. Thus, instead of relying on warning equipment triggered by a train’s approach, lineside equipment initiates the warning sequence at level crossings by predicting a train’s arrival time based on its positioning and speed data. This system closes the barriers, and after a train has passed a level crossing, it sends a signal to restore the level crossing to a non-warning status. Finally, the system can automatically restrict entry to tracks closed for construction and maintenance either by distance or as a block section of track. Development of ATACS took 10 years and it went through three phases from 1995 to February 2005. Currently JR East is installing ATACS with the aim of starting in-service use in several years. JR East plans to standardise Atacs as the Japanese Industrial Standard code, and to demonstrate and export it globally, as ATACS has an excellent performance level, equivalent to ERTMS ETCS Level 3, and should provide an equally capable alternative. IRJ Radio antenna. Onboard control equipment. Onboard transponder. Onboard radio equipment. Tachometer generator.
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