A locomotive, car, or caboose that is marked as Bad Order (BO) has been damaged, and requires repair at a Repair Track. When a train enters a map with bad ordered vehicles, a warning will be displayed.
Vehicles may become bad ordered either randomly or through a collision. Random bad orders only occur for cars.
Random bad orders
Damage can occur to a car simply through normal wear and tear. Wheels, axles, and bearings wear out and need replacing, brakes must be kept carefully adjusted, and car bodies rust over time. When travelling between maps, a car may randomly be declared bad order. The chance that a car becomes broken depends on the distance between the maps, and also how many miles the car has travelled. The base rate is 0.01% per thousand miles, which increases to 1% per thousand miles after 200,000 miles of travel.
Locomotives and cabooses are not affected by random bad orders.
If two trains couple at more than 20mph, they will become damaged due to the excessive forces (and, in real life, would likely derail). The two vehicles at the ends of the trains that meet will be damaged, and require repair.
Cars that are bad ordered cannot be loaded until they are repaired, as shippers will refuse to load their goods into a car that is clearly unserviceable. If a block with the special Bad Order filter is specified in the Block Filter, bad ordered cars will be allocated to that block instead of the block they would normally be assigned to.
Locomotives that are damaged will not provide any power until repaired. A train with no working locomotives will be unable to leave the current map until the locomotives are repaired, or extra locomotives are attached.