Reply to "Rolling Stock Weight standard"

For optimal operation, lighter cars should be placed at the end of the train.  This will reduce drag/rolling resistance on the rear, thereby reducing the "stringlining" effect (the train trying to pull itself straight while going through curves) which can lead to derailments.  Having as wide of a radius of curves as possible and avoiding S curves (or having transitions between the divergent curves as long as the longest car on your roster) also helps.