Wheel wear is a concern on most metro systems.

对大部分地铁系统来说车轮磨损事关重大。

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Although there are popular urban metro systems, railway infrastructure is limited.

尽管城市地铁系统人气十足，铁路基础设施依然是很有限的。

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The larger cities have metro systems in operation, under construction, or in the planning stage.

较大的城市有地铁系统在运行，正在建设中，或在规划阶段。

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This month TDSi won a contract to make control equipment, readers and software for 12 subway stations in Beijing, having already supplied kit for metro systems in Shanghai and Tianjin.

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Even with the light rail systems, these metro areas are still more friendly to drivers than non-drivers.

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But both MTA railroads maintain comprehensive inspection programs on their tracks, according to the MTA. Every two weeks, workers visually inspect "every inch of track" on both Metro-North and Long Island Rail Road systems for defects, an MTA official said.

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