Black Mesa Transit System

A Monorail is a transportation system based on a single beam. The term is also used variously to describe the beam of the system, or the vehicles travelling on such a beam or track. In Half-Life, the Black Mesa Research Facility features an extensive monorail network known as the Black Mesa Transit System, linking the many different sectors of the facility. The transit system is the primary form of transportation throughout the facility.

Overview
The monorail system in the facility is extensive and complex, resembling a maze at times. Entire rail tunnels lay abandoned in sections of the facility that have been decomissioned. There are three kinds of monorail cars in the game: A passenger variety, with seats, windows and an electric door, a freight variety with a control console at the front and a flatbed for carrying cargo, and a bulky, heavy variety presumably used for pulling large volumes of cargo behind it. These vehicles feature prominently in Half-Life and also both expansions, with the protaganists of all three games using them both before and after the catastrophe to get around the facility. Gordon Freeman, for example, rides into work on one shortly before the incident, and later uses a freight car to circumvent a maze of tunnels in a decomissioned part of the facility in order to escape the HECU.