Its major function are in maintenance, direction - turning frame maintenance, temporary repair, big maintenance, rough parts maintenance, wayside equipment maintenance and new vehicle assembling.

主要功能为列事大修转向架检修临时检修，大维修粗件修护道旁设施维修及新车组装。

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Therefore, full safe clearance is never done during the day (except in emergency repair situations), and nighttime is the only time all the major maintenance work can be completed.

FORBES: Why Does BART Need To Do Nightly Maintenance?