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       Beijing Metro Line 1 is the first metro in New China. It is in a straight line along Chang'an Avenue and passes through the most prosperous section of the city center. It is responsible for the passenger flow connection and transfer tasks of multiple lines. It is one of the urban rail transit lines with the largest density in China. Its average daily passenger volume exceeds 1 million. As one of the busiest lines in Beijing, Line 1 cannot be interrupted during the signal renovation period. Therefore, the construction and testing of the signal are carried out after the suspension of operation at night. The construction time available is less than three hours, and it also involves the maintenance of existing equipment and professional cross-construction. The renovation, therefore, is more difficult and challenging. It’s the largest signal renovation project in China currently.