What authority is required for a train to operate against the current of traffic?

When a train is required to operate against the current of traffic, it must have the appropriate authority to ensure the safety of all operations. Train order and compliance with timetable speed restrictions provide that necessary authority. Specifically, train orders serve as directives given to train crews, allowing them to carry out operations such as running against the current of traffic, which is critical for maintaining safety and coordination on the railway.

Abiding by timetable speed restrictions is equally important in this context, as it ensures that the train does not exceed safe operational speeds while moving in a potentially hazardous direction. This combination of train orders and adherence to established speed limits enhances operational safety and helps prevent accidents.

Other options may include various forms of communication or permissions that are generally important in certain operational contexts, but they do not specifically encapsulate the formal and structured authority needed for operating against the current of traffic.