Workers conduct maintenance work on the rail in Shanghai, east China, Aug. 7, 2018. Maintenance staff of railways here remain at their posts in the heat to ensure the safety of passengers. (Xinhua/Chen Fei)

Workers conduct maintenance work on the rail in Shanghai, east China, Aug. 7, 2018. Maintenance staff of railways here remain at their posts in the heat to ensure the safety of passengers. (Xinhua/Chen Fei)

Workers check the rail in Shanghai, east China, Aug. 7, 2018. Maintenance staff of railways here remain at their posts in the heat to ensure the safety of passengers. (Xinhua/Chen Fei)

Workers check the rail in Shanghai, east China, Aug. 7, 2018. Maintenance staff of railways here remain at their posts in the heat to ensure the safety of passengers. (Xinhua/Chen Fei)

Workers conduct maintenance work on the rail in Shanghai, east China, Aug. 7, 2018. Maintenance staff of railways here remain at their posts in the heat to ensure the safety of passengers. (Xinhua/Chen Fei)

Workers conduct maintenance work on the rail in Shanghai, east China, Aug. 7, 2018. Maintenance staff of railways here remain at their posts in the heat to ensure the safety of passengers. (Xinhua/Chen Fei)