There is also Route Map at Laufach underpass to second platform which acts like trap, you can get down and collect it, but you can't use stairs to get out on both sides then.
Anyone who can't wait for the fix. Just got it some minutes ago by doing the following. Thanks for the hint: neal08ni Use the MP36PH in scenario planner and head towards Rockwood. A few meters after the collectible there are white flowers that stick out over the fence. Stop the loco (cabin) exactly at this white flowers, open the door and "run" out of the cabin by holding the "Run"-Button (Shift / RT / R2). Because the cabin is high enough you are able to jump (run) over the fence. Then you can collect the hat. Edit: Be aware to save before doing this, because you cant get back anymore.