Central subway

Boston's central subway is the system of tunnels through which the MBTA Green Line operates light rail transit (LRT or "trolley") service in the urban core of the city. The central subway comprises several tunnels built at different times, including the Tremont Street subway, the Boylston Street subway, and the Huntington Avenue subway. Boston's subway operator, the MBTA, sometimes also refers to the Red Line and Orange Line heavy rail tunnels as part of the central subway tunnel.

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Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).

Other tunnels in United States

Delaware Aqueduct United States · 137 km Päijänne Water Tunnel Finland · 120 km Orange–Fish River Tunnel South Africa · 82.8 km Ishikawa Tunnel Japan · 78.5 km Brenner Base Tunnel Austria · 64 km Mont d'Ambin base tunnel France · 57.5 km Gotthard Base Tunnel Switzerland · 57.09 km Hong Kong–Zhuhai–Macau Bridge China · 55 km