What is the most damaging outcome of a train not rolling freely during a terminal test?

When a train does not roll freely during a terminal test, the most damaging outcome is flat wheels. Flat wheels occur when a train is unable to roll smoothly, often due to excessive friction between the wheel and the rail. This can happen if the brakes are applied incorrectly, if the bearings are binding, or if there is a mechanical issue that restricts movement.

Flat wheels result in significant damage to both the wheels themselves and the railway infrastructure. Once flat spots develop on the wheels, they can cause vibrations, increase wear on the rails, and can lead to a more serious and costly problem if not addressed. The train will require wheel replacement or repair, which can be time-consuming and expensive.

Understanding this issue highlights the importance of ensuring that trains are able to roll freely during testing. It establishes proactive measures taken by operators to maintain both the trains and the tracks, preventing further complications that may arise from issues like flat wheels. Other potential outcomes, such as electrical failure, brake lining damage, or loss of cabin pressure, are certainly important but do not have the direct and immediate physical impact on the train's operational integrity like flat wheels do.