平均起来，一条钢制履带的履带板使用400公里（250英里）之后就必须维修或更换。
On average, the segments of a steel track must be repaired or replaced after just 400km (250 miles) of use.
地铁正在进行维修，有时两列对开的地铁只能轮流共用一条轨道。
The subway is undergoing repairs, and sometimes trains going in opposite directions take turns using the same track.
它包括247个坑屋（pit houses）、27个窖房（pit rooms），866个维修点（pits），11条小运河，1个球型场地（ball court），四个砖墙。
The project had identified 247 pit houses, 27 pit rooms, 866 pits, 11 small canals, a ball court, and portions of four adobe walled compounds.
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