Finding the Entrances
The Freight Transit Line is a vast underground rail network beneath the map. Entrances are scattered across the world -- some built into existing monuments, others standalone and procedurally placed.
On your map, every tunnel entrance shows as a small white circular icon with a train-car emblem. Head to one and you'll find huge spiral staircases descending into the terrain, with a faster (but more exposed) elevator shaft in the centre. Either gets you down.
Descending to the Platforms
Reaching the bottom of the first shaft doesn't put you on the rails yet. You traverse a series of corridors -- watch for Tunnel Dwellers here -- to another elevator and staircase, then follow the signs down to the platform.
Once on the main level, open your map: it switches to a subway-style display of the entire tunnel system, so you can plan routes between stations. The wider, unlabelled sections between platforms are alcoves -- they hold extra loot and NPC spawns.
Tunnel Dwellers
Tunnel Dwellers are the underground NPCs, dressed in a Jumpsuit and Gasmask. Each has 125 HP and carries an M92 pistol or an M39 rifle. Like other NPCs they don't drop the weapon they're holding -- instead you get components, electrical parts, ammo, and the occasional bear rug.
They cluster in the corridors leading to platforms, around the platforms, and in alcoves. Difficulty scales with depth: deeper tunnels have tougher Dwellers but better loot.
Loot
The tunnels are a reliable early-to-mid-game scrap and component farm, and they're accessible to minimally geared players willing to brave the dark.
Around the platforms and in the alcoves you'll find three kinds of loot box: common wood crates, tool boxes, and the occasional Military Crate. Combined with the components and ammo off the Dwellers, a tunnel run nets solid crafting materials and scrap without needing top-tier gear.
Deeper platforms carry more Dwellers but progressively better loot, so weigh the risk against your gear and ammo before pushing in.
Workcarts — Driving the Rails
Each station has two workcarts facing opposite directions. They run on Low Grade Fuel, have 6 throttle settings (3 forward, 3 reverse), and keep running even after you leave the cab. A separate Underground Workcart spawns in side-station cubbies labelled "Maintenance Room".
Driving hazards: - NPC barricades block the track -- slow down (a proximity alarm sounds), as hitting them or another cart at speed damages your cart. At low speed you break through barricades cleanly. - At track junctions, use your left/right strafe key to choose which line to follow. - Damage slows the cart; repair it with a Hammer and metal fragments. When a cart's engine is destroyed, any fuel inside is lost.
The underground network now connects to the surface rail via Transition Track Tubes, so a workcart can take you across the map and back up top -- fast travel that skips the dangerous roads.