Railway Signaling Systems

Multiple Aspect Colour Light Signalling (MACLS)

• All signals must be electrically lit, eliminating phantom indications.
• Main signals are multi-unit colour light; shunt signals are position light. Calling signals are optional based on operational needs.
• Signal types and standards should be uniform across stations and level crossings within a section, matching the section's maximum permissible speed. End-station signaling should be consistent as much as possible.
• Signal numbers and heights should be kept to a minimum necessary for safety and operation.
• Signals are typically on the left or above the relevant track; right-hand signals have directional arrows.
• Signal placement and alignment prioritizes: clear visibility for approaching locomotives; minimizing the chance of one signal aspect being confused with another; and avoiding confusion between main, subsidiary, or other lights. Subsidiary signal lamp size/LEDs should be smaller than main signals and not brighter.

Signal Location and Spacing

• Block overlap must be at least 180 meters for MACLS.
• Signal overlap must be at least 120 meters. Method of reckoning is detailed.
• Overlap beyond the IB signal (Class C station) must be at least 400 meters beyond the IB home signal. Specific rules are defined.
• Signals must offer minimum visible distance: 400 meters for distant signals; 200 meters for stop signals. Visible distance limitations should be accompanied by speed restrictions. Inner distant signals visible from 200 meters.

Signal Aspects

• Distant signal aspects differ in single and double distant territories.
  • Single distant: yellow (bottom) for caution; two vertical yellow lights for attention; green for proceed.
  • Double distant: two vertical yellow lights for attention; green for proceed. Inner distant signal displays aspects as in single distant territory. Special instructions may allow combining the distant signal with other signals.
• Stop signal aspects: red for stop; yellow for caution; two vertical yellow lights for attention; and green for proceed.
• Typical station signal aspects are outlined. Detailed descriptions are given for different situations (e.g., main line, loop line).

Signal Placement and Related Concerns

• Distant signals are placed a considerable distance behind the first stop signal (at least 1 kilometer in single distant, 2 kilometers for doubled distant and 1 kilometer distance for inner) in consideration of emergency braking distances.
• Home signal placement is behind any track connections, at least 180 meters from the furthest obstructed point after line-clearance is granted. Special considerations apply for gradients.
• Routing signals are placed behind points that control routing.
• Starter signals (one per converging line) protect adjacent lines.
• Starter indicators (optional) repeat starter aspects.
• Intermediate and advanced starter signals placement criteria are detailed for single and double line sections.
• Gate stop signals are placed at least 180 meters behind the gates they protect.
• Intermediate Block stop signals are at an intermediate block post on double or single line, and are spaced to divide the block section roughly in half.
• Automatic signals are spaced approximately one kilometer apart.

Signal Sequence & Coordination

• When a stop signal is displayed, signals further back cannot show a less restrictive aspect than caution.
• Multiple aspect signals displaying caution must be adequately spaced from the next signal ahead—at least 1 kilometre. Caution aspects are repeated on successive signals for closer distances.
• For metro, distances accommodate maximum emergency braking and ruling gradients. Special consideration is provided when signals lack adequate distance in double distant territories.
• Combined signals (allowing stop, caution, attention, and proceed aspects) may be provided under special instructions.
• Special consideration is given to diverging and converging lines.

Subsidiary Signals

• Calling-on signals caution trains to proceed ahead cautiously after stops, even if signals are green. Calling-on signals are indicated by yellow light instead.
• Shunt signals control shunt movements. Lights are white and horizontally aligned in the 'ON' position, and diagonal in the 'OFF' position. Signals can be located separately or below stop signals.
• Installation methods for calling-on and shunt signals are included.
• Detailed rules about timing and operation of signalling for calling-on signals are listed (including train stops and track circuits).