Restrictive signals indicate that a train can proceed but only under specific conditions, such as reduced speed. These signals help manage speed within certain sections of the track.

Location and Display of Absolute Signals

These signals are strategically placed along railway tracks at junctions and critical points to ensure their visibility to train crews. Absolute signals can be displayed in various forms, including:

Color Light Signals

Color light signals use different colored lights to convey specific messages. For instance, a red light signals a stop, while a green light indicates permission to proceed. Other colors like yellow are often used to convey a cautionary message.

Semaphore Signals

Semaphore signals use moving arms to indicate the status of the track. A horizontal arm typically indicates a stop, while an angled arm suggests that a train can proceed with caution.

Operation and Safety Systems

The operation of absolute signals is usually controlled by a centralized signaling system that can be either manual or automated. This system ensures that signals accurately reflect the current state of the track ahead of the train. Absolute signals are part of a broader safety system in railways, often used in conjunction with other safety mechanisms such as track circuits and interlocking systems to prevent accidents.

Examples of Absolute Signals in Different Railway Signaling Systems

Different countries have their own railway signaling systems, each with its unique characteristics. Here are a couple of examples from the UK and Japan:

UK Railway Signaling System: Absolute Block Signalling

UK railways use a signaling system called absolute block signaling to manage train movements. Key components include block signals, home signals, and start signals. Block signals act as permissive signals, indicating that a train can proceed if there is no visible train in the block. However, if the block signal shows a red light, the train must come to a stop and can only proceed if the signal is confirmed to be faulty or if a hand signal is given.

Japan Railway Signaling System: Absolute Signals in Automatic Block Signal System

In Japan, absolute signals are part of the automatic block signal system. These signals are either block signals, home signals, or start signals. Block signals do not allow two trains in the same block, and if a train encounters an absolute signal displaying a red light, it must come to a complete stop, even if the signal appears to be malfunctioning. Home signals allow trains to enter a station, while start signals permit trains to depart from a station.

For instance, consider a scenario where a train approaches three absolute signals displaying R, R, and YG. The YG signal on the middle column is actually a combined signal indicating that the route to the right or left is blocked, but the track ahead is clear. Therefore, the train must come to a complete stop and cannot proceed, even if it has stopped for a considerable period. This is because the signal is considered absolute and must be obeyed.

To pass an absolute signal displaying a red light, there are two methods available:

Substitute Hand Signal

A substitute hand signal, controlled by a human, can override the signal if waved by a signalman. This provides an emergency override in case of signal malfunctions.

Subsidiary Signal (Call-on Signal)

In some cases, a subsidiary signal called the call-on signal can be used, particularly for coupling trains within a block. If a train wants to couple with a train that is stopped, it can pass the red signal if the call-on signal is illuminated, allowing it to proceed at a speed of no more than 15 km/h without disabling the ATS (Automatic Train Stop) system.

In conclusion, absolute signals are critical components of railway signaling systems, helping to maintain safe train operations by clearly communicating the status of the track to train operators. Understanding the operation, types, and display of these signals is essential for ensuring the safety and efficiency of railway systems.