Train Sim World 3

The fastest way I found to complete this is through custom scenarios. From the Main Menu -> Creators Club -> Scenario Planner -> Training Center.

From there create a new scenario with "Off the Rails" enabled. Press to add a new service. Select Start Marker as "Station One Platform 1", Select Path "Switch Line 2 to Main Loop 1", Select Destination "Main Loop Track 1", Select Instructions "Main Loop West 1", Confirm Service, Select BR187 DB, Select Formation "DB BR187 Light Locomotive", enter a Service Name and Confirm, and finally press to save and exit.

Now you will see your new scenario listed. Click on it and select play. Get the locomotive moving and apply full throttle. I would then save, exit, and resume from the main menu. The reason is when you first start it the tracker doesn't always track right. I found starting from a save it would continually track progress. Now plug your controller in and let it sit looping around the training center picking up those kilometers. Should take about 3-3.5 hours to complete depending on pervious progress towards the achievement.

I do recommend completing the follow achievement first as not to waste time.