Railway Signalling Systems Basics

Here are the study notes for the text:

• Why Railway Signalling Systems Exist*

• Two fundamental physical reasons:

  • Trains are guided by the track and must be routed to avoid collisions with each other
  • Trains cannot stop within the distance that the driver can see, so prior warning is needed to slow down and stop

• Signalling System Basics*

• Block System: Basis of all UK signalling systems

  • Each line divided into block sections, with only one train allowed in each section at a time
  • Signals provided at start and end of each block section to allow trains to enter and exit

• Functions of a Signalling System*

• Safety Functions:

  • Prevent trains taking conflicting routes
  • Maintain safe separation distance between trains
  • Protect trains from driver malfunction (incapacity, inattention, misjudgement)
  • Ensure trains do not exceed permitted speed

• Non-Safety Functions:

  • Maximize track usage
  • Route trains automatically and regulate their flow
  • Provide data for passenger information purposes

• Generations of Signalling Systems*

• Mechanical Signalling: 1860s technology, still in use on some regional lines

• Multiple Aspect Signalling: Predominant system in use, covers virtually all main lines in the UK

  • Developed to increase train carrying capacity and enable single signaller to control larger area
  • Functionality of mechanical stop and distant signals combined into a single colour light signal

• Cab Signalling: Next generation of signalling, signals are displayed in the driver's cab

• Mechanical Signalling*

• Uses mechanical levers and rods to operate signals and points

• Signals are of the semaphore type, with two key types:

  • Stop signals: require the driver to stop if the signal arm is horizontal
  • Distant signals: advise the driver to slow down if the arm is horizontal, or proceed at linespeed if the arm is raised

• Typical mechanically signalled layout illustrated

• Multiple Aspect Signalling*

• Combines functionality of mechanical stop and distant signals into a single colour light signal

• Signals have three or four aspects:

  • Red: requires the driver to stop
  • Single yellow: advises the driver to slow down, as the next signal is at red
  • Double yellow: advises the driver to slow down, as the next signal is at yellow
  • Green: advises the driver to proceed at linespeed

• Typical sequence of aspects illustrated

• Components of a Signalling System*

• Train Detection:

  • Manual detection: original method of detection, signaller observes train from signalbox window
  • Track circuits: use insulated sections of rail as an electrical circuit, which the wheels of a train shunt as it enters and leaves the section
  • Axle counters: detect the number of axles entering and leaving a section of track

• Point Operating Mechanisms### Signalbox Control and Display Systems

• There are two key types of signalbox display systems, excluding mechanical signalling.

• One type is a panel display system, which consists of a mimic of the track layout etched onto small metal tiles.

• The signaller can control signals and points using individual buttons and switches, and receives information on the system's state through illuminated displays within the panel.

• Many panel signalboxes are in use in the UK, covering hundreds of route miles each.

VDU-Based Displays

• VDU-based displays are a logical extension of panels, utilizing VDU technology to provide the same and sometimes enhanced information.
• The signaller's control interface is via a keyboard and mouse.
• This is the predominant form of control and display system for new signalling systems.

Ancillary Items

Location Cases

• Location cases are lineside steel cases containing power supplies and control equipment for signals, points, axle counters, track circuits, etc.

Train Describers

• Train describers are non-safety critical computer systems that display a unique alpha-numeric description of each individual train to assist the signaller with routing decisions.
• They obtain train location and movement information from the signalling interlocking.
• Train describers can port train movement data onto a range of further systems, including automatic route setting systems, passenger information systems, and train performance monitoring systems.

Level Crossing Protection Equipment

• Level crossing protection equipment includes road lights, barriers, and CCTV monitoring systems to manage and control conflicts between road and rail vehicles at level crossings.

Cab Signalling

• Cab signalling is the next generation of signalling systems, aiming to abolish lineside signals and provide comprehensive displays in the driver's cab to indicate the speed and limit of authority to move.
• Cab signalling systems ultimately aim to replace infrastructure-based train detection by enabling the train to know its precise position and report it to the signalling system via a secure high-reliability radio link.
• The key system is ERTMS – European Rail Traffic Management System.

Learn about the fundamental physical reasons behind the existence of railway signalling systems, including block systems and safety measures. Understand the basics of railway signalling and its importance in preventing collisions.