The brown routes on the jepp charts are Drift-down/Terrain clearance dispatch routes. Meaning that if you are filed over those routes you must be dispatched under either:
1. Terrain Clearance (If you lose an engine, terrain clearance will still be assured)
or
2. Drift-Down (If you lose an engine, you will proceed to one of your driftdown alternate airports because you won't be able to maintain the required terrain clearance)