The Tremont Street Subway in Boston opens, becoming the first underground rapid transit system in North America.

The Tremont Street subway in Boston's MBTA subway system is the oldest subway tunnel in North America and the third-oldest still in use worldwide to exclusively use electric traction, opening on September 1, 1897. It was originally built, under the supervision of Howard A. Carson as chief engineer, to get streetcar lines off the traffic-clogged streets, instead of as a true rapid transit line. It now forms the central part of the Green Line, connecting Boylston Street to Park Street and Government Center stations.

Rapid transit or mass rapid transit (MRT) or heavy rail, commonly referred to as metro, is a type of high-capacity public transport that is generally built in urban areas. A grade separated rapid transit line below ground surface through a tunnel can be regionally called a subway, tube, metro or underground. They are sometimes grade-separated on elevated railways, in which case some are referred to as el trains – short for "elevated" – or skytrains. Rapid transit systems are usually electric railways that, unlike buses or trams, operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles.