Even after the last metro stops rolling, the work doesn’t stop. Maintenance crews take over to keep the Shanghai Metro running like clockwork for the 10 million passengers who ride it every day. Editor’s note: This is the second in a series to mark the Shanghai Metro turning 30. Readpart one.By Lü Xiao, Xue Haolin and Wu Huiyuan Download the new Sixth Tone app at the App Store or Google Play APK file for Android:https://image4.sixthtone.com/pkg/sixthtone.apk (Copy URL and open in browser)