From Halopedia, the Halo wiki
A tram is a form of rail transportation, featuring a passenger vehicle moving on one or more tracks. The power for the tram car can be drawn from the rail itself or a separate power line running along the track.
A tram system was featured as a method of transport for the secret ONI excavation site under Sword Base on Reach. The tram could change its orientation, descending into the main cavern vertically, much like an elevator. The tram also featured a holographic viewscreen on its forward window. During the Fall of Reach on August 29, 2552, Noble Team rode the tram to the excavation, while Dr. Catherine Halsey revealed them the true nature of their mission.
The Orbital Defense Platforms and other large orbital platforms feature a tram system that encompasses the facility, with several stations along the way. Moments before the Battle of Earth on October 20, 2552, John-117 and SgtMaj Avery Johnson rode a tram from Cairo Station's armory to the command center. Large UNSC vessels, such as the colossal UNSC Infinity, are equipped with onboard tram systems for transport across the expanse of the vessel.
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