Biodome Complex
The Biodome Complex is is a location featured in Opposing Force in the chapter Vicarious Reality. It is a large facility that contains a series of simulated environments where captured aliens and flora are kept and observed in artificial recreations of their natural habitats. Alongside these enclosures are laboratories where scientists perform studies and tests on the creatures in closer detail.
 Materials Transport
The Subsurface Materials Transport System, also simply known as the Materials Transport, is a location featured in Half-Life and Opposing Force in the chapters Power Up, On A Rail, and Friendly Fire. It is a large decommissioned underground rail system, which consists of a network of train tunnels, storage areas, and offices.
 Track Control
The Track Control is a location featured in Half-Life in the chapter Power Up. It serve as a control station for the rail tracks of the Materials Transport system. It consists of maintenance areas and a generator that supplies power to the rail tracks. It is possible that the area was used for the maintenance of rail carts.
 Lambda Sector Transport
The Lambda Sector Transport is a location featured in Opposing Force in the chapter Friendly Fire. It is a sub section of the Materials Transport B and serve as a secured access for the Lambda Sector. The nearby areas include an office area and an Ordinance Storage Facility above the offices.
 High Altitude Launch Center
The High Altitude Launch Center is a location featured in Half-Life in the chapter On A Rail. It consists of Silo E, a silo converted into a fully-functional satellite delivery rocket launchpad (the Satellite Rocket Loading Bay), and the Launch Control building. This is used by the Lambda Team, with the help of Freeman, to launch the satellite that later help revert the Resonance Cascade.
 Sector E Line
It is connected to the Green Line of the Black Mesa Transit System.. Connected to Area 9 Security Checkpoint, that Black Mesa Transit System line is located below the Sector B Line and above the Sector C Line. Its directions are unknown.
 Sector E Subsurface Transport
Level A of this Black Mesa Transit System section can be accessed from Sector C Line, where the G-Man is first seen in Half-Life, and leads to an unnamed area where the first Shock Trooper a zombie security guards are encountered.
 Behind the scenes
Half-Life includes several unused signs for the Track Control and the Materials Transport. According to these textures, both locations were originally part of Sector D. There was to be a Train Hub in the Track Control; an Administration area with three levels, and Loading Bays in the Materials Transport.
The unused Materials Transport sign "c2a2a_sign2b", which says Subsurface Transport Level A, was recycled for Opposing Force, and it appears in the Sector C line of the transit system. The filename prefix indicates that the sign was to appear in the second map of the chapter On A Rail.
 Easter eggs
In Half-Life, Dave Riller's name, a level designer who worked on the Materials Transport levels, appears in the map c2a2c, under grates, which can be entered from a hole under the stairs. This was removed in the console ports of the game. In Opposing Force, the names S. Jones and S. Reardon appear in an office found near the Lambda Sector Transport. These are nods to Gearbox employees Sean Reardon and Steven Jones.
 List of appearances
- Half-Life (First appearance)
- Half-Life: Opposing Force
- Half-Life: Blue Shift (Black Mesa Transit System map only)
|Half-Life story arc journey||Succeeded by|
Biological Waste Processing Plant
Black Mesa Transit System
|Half-Life: Opposing Force story arc journey (1)||Succeeded by|
|Half-Life: Opposing Force story arc journey (2)||Succeeded by|
Waste Processing Area 3
|Half-Life: Opposing Force story arc journey (3)||Succeeded by|