The Call of Duty blog has details on the Classified Arms Reloaded update coming tomorrow to Call of Duty. Among other things, this adds a new fast travel system to the Call of Duty: Warzone that's part of an effort to shake up the meta in the battle royale. The update includes new perks, items, a new time-limited mode coming to Call of Duty: Vanguard, and more. Here's more on the fast travel system:

To travel via mine cart to another hub area, simply interact with the circular hatch and walk toward the cart. When doing so, the destination name will appear on your screen — you can also check the map to see how it interacts. After a few seconds of travel time, you’ll instantly appear at your destination . . . Hopefully with no enemies waiting on the other side.

Those in the know — like you, after reading this section — can use light and audio clues to figure out if an enemy is on the other side, or if the circle collapse will soon engulf the destination. As with most situations, when there is a green light, it means it’s safe. Anything else can mean potential danger, and if the indicator is off with gas going through the vents, then that means you cannot travel to that destination.

Mastering this system may be key to the new meta after this update, so learn it and its not-so-secret indicators well.