What do cab signals govern in terms of train movement?

Cab signals primarily serve to govern block signal usage by providing real-time information to the train crew about the conditions of the track ahead. These signals convey critical data regarding whether the blocks ahead are clear, occupied, or if the train should reduce speed or stop. This mechanism ensures that train operators are aware of the current status of track blocks, enhancing safety and preventing collisions.

In the context of this function, cab signals operate as a part of the signaling system that helps train crews make informed decisions while they are in motion. This direct transmission of information helps maintain safe distances between trains and allows for smoother operations in busy rail networks.

The other choices pertain to different aspects of train operations, such as speed management which relates more to the train's operating speed rather than the signaling system, current of traffic which involves general train movement patterns, and track maintenance which is focused on the upkeep and repair of the rail infrastructure. These aspects do not directly correlate with the specific governing function of cab signals in relation to block signals.