In real life you MUST apply hand brakes and in many caes cars/wagons that have no hand brakes applied will 'run away'. If a difficulty level was introduced at some stage this could be in the Master level and Senior Engineer/driver level. It would be nice to have (maybe there is already) wagons/cars that actually run away. It reflects real life operations. So the idea here is if you are at the top levels as above you need to apply hand brakes or your cars/wagons will roll away and cause a possible accident/disaster. Even if you leave a wagon for just 5 minutes you will find 100% of railways on earth now have a mandatory hand brake policy. The air brake will hold it for a few hours, EP (new electronic pneumatic brakes) will hold it for only 90 minutes.... so these days safety is primary.
