Widely-distributed train-traffic computer control system and its step-by-step construction

In a large scale mission critical real time control system, such as the Tokyo metropolitan area train traffic system, it is very difficult to construct the entire system at once. Moreover economic considerations makes year by year investment inevitable for developing the system. The new Tokyo metropolitan area train traffic computer control system, supplying service to 19 train lines, 300 stations and 6200 trains per day, has been constructed step by step over 8 years without halting train operations. Here the computer system is required to be expandable online during system operation and without disrupting already constructed subsystems. To enable testing during system operation, an autonomous decentralized online expansion technique is proposed. Then the effectiveness of the technique is demonstrated in a real system