The MSTS Activity Editor allows you to make your own activities, or missions, for the player to complete. This is also how you can get lots of other trains running while you drive yours!
I have had several activities crash with messages along the lines of "Failed to Initialise Car <200309> RigidBody". Sounds like a consist problem but all the rolling stock I'm using works OK elsewhere. Can anyone shed any light on this and how to cure it?