Much of the Metrorail system, which opened in 1976, runs below ground, including a section that goes under the Potomac River between Washington and Virginia and one that goes over it.

大多数于1976年投入使用的地铁线路都是在地下的，其中有一段在Potomac河(一条流经华盛顿特区的河，译者注)下面，穿过华盛顿特区和弗吉尼亚州，还有一段则在地上横跨Potomac河。

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Washington's Metrorail is expanding its hours, starting service at 4 a.m. on Inauguration Day.

CNN: Washington locals excited, but bracing for inconvenience