[iggldiggl]

> Train tracks are normally not precise to within 4mm anyway

Yes they are. Of course practical tolerances including allowances for wear and there are large enough that things can be made to work, but in terms of nominal construction tolerances for example, 4 mm can easily eat up all your construction tolerances or even exceed them.

[sidewndr46]

I obviously don't have a in depth knowledge of Finnish rail, but have you ever looked at rail in the US? I can show you tracks with completely missing ties. Tracks that move vertically by a foot when the train goes over them. Tracks that visually snake all over the place. The difference is made by slowing down the train. Derailment at 3 mph rarely matters. The biggest risk is the conductor doesn't know it happened & continues to drag the car along the tracks

[iggldiggl]

Sure, but even in the US that infrastructure state is usually only found on minor branch lines (shortlines), not on the main lines.