From Halopedia, the Halo wiki
The Tunnel Weasel is a rail vehicle, or tram, that is used by the Montero Vitality Center to traverse the tunnels of the Montero Cave System.Though it rides the tracks already laid out, the Tunnel Weasel's driver can switch between tracks to take the tram to different locations throughout the network. The driver can also switch gears. It is powered by electric engines and it interfaces with the tracks with rubber tires. Tunnel Weasels can consist of at least three cars, including a tractor unit. These cars are capable of being unhitched from the rest of the tunnel weasel and reattached later. Tunnel Weasels are used to transport both supplies and passengers, who ride along on pairs of benches. These benches are at least present on the tractor unit, if not on the other cars as well.
List of appearances