Which type of signals are primarily used on railways?

Block signals and interlocking signals are the primary types of signals used on railways to ensure safe train operations and maintain proper spacing between trains. Block signals are strategically placed along the railway to indicate whether the track ahead is clear or occupied, helping train operators make informed decisions about their speed and movement. These signals are crucial in preventing collisions by providing clear visual indications of track status.

Interlocking signals serve a specific function in managing train movements at junctions and crossings. They ensure that conflicting train movements cannot occur at the same time, thereby maintaining safety and efficiency within the rail network. The use of interlocking signals helps coordinate the flow of trains, especially at complex rail junctions.

In contrast, the other types of signals listed don't serve the same purpose in rail operations. Flash signals and warning signs might be used for pedestrian safety or alerting drivers at level crossings, traffic lights and street signals are primarily for vehicular traffic control, while signal whistles and bells are more about auditory signals than visual indications for train operation. Therefore, block signals and interlocking signals are essential elements of railway signaling systems.