Train Sim World 2

As daunting as this achievement seems, the good news is that it's cumulative across all trains and not just a specific model as I originally thought.

However if you are gunning specifically for this achievement start up Schnellfahrstrecke Köln-Aachen and run any route that uses the DB BR 406 ICE 3M as this is the quickest train included in the base game.

It has just came to my attention that this tracks with routes you make in scenario planner. By selecting tools after selecting a route you can create a nonstop route from one end of the route to the other. This can be done on the route I mentioned above but would recommend using this method on the LGV Méditerranée (if you have this DLC) as this is the longest high speed route in the game so far (93km, 300kph speed limit) While creating a scenario you can select an option labeled 'Off the Rails' this allows you to use any train on the selected route which can help with any other driving distance related achievements you may be working towards.

I'm using the 9:43 service to Bruxelles Midi to AFK this. Just set the AFB to 140kmh and auto drive from start to end and make a save as soon as you're rolling. There are some sections where you'll overspeed, but for the majority of the track, 140kmh is good enough. Once you run the red signal at the end, just load your save and go do other stuff for 40 minutes.