1. Green Aspect: Clear, proceed normally at Permissible speed*
2. Double Yellow Aspect: Preliminary Caution, proceed expecting Caution at next signal
3. Yellow Aspect: Caution, proceed and preparing to stop at next signal
4. Red Aspect: Danger, stop.

A Signal outside Reading station, Signal No. T 1698 to be precise, displays a clear aspect (above), allowing the Class 166 driver to pull away. After they have done so, the signal will drop back to a danger aspect (below).

A demonstration of the typical aspect sequence after a train has passed the signal in question, which in this case, is T 483 which stands on the Down Relief line at Iver station.

Defensive Driving

Feathers and Route Indicators

1. Green Aspect: Clear, proceed normally at Permissible speed
2. Flashing Double Yellow Aspect: Preliminary Caution, proceed initialising brake towards upcoming speed restriction as indicated
3. Flashing Yellow Aspect: Caution, proceed, continue to brake towards speed indicated, expect feathered aspect at next signal
4. Feathered Aspect: Clear/Caution, proceed expecting diversion at next junction as indicated by feather, drive in accordance with relevant signal aspect

This feathered route indicator tells the driver that they are diverging to the left under a double yellow ‘caution’ signal. Note that there are multiple possible feathers in some instances, each one corresponds with a different diverging route option. If no feather is lit, no diverging is expected.

A prime example of a ‘theatre’ route indicator, seen here on SN 5 at London Paddington. The Green aspect denotes clear, and the ‘1’ tells the driver which of the lines they will be routed down. This information is very important, there are so many lines out of Paddington that spotting which signal is yours can be a challenge – knowing your path can let you know where to look down the line.

Banner Repeaters

1. White Horizontal Banner: On, the signal it applies to is set at danger
2. White Diagonal Banner: Off, the signal it applies to is set to a proceed aspect
3. Green Banner: Off, the signal it applies to is set to specifically a green aspect

Two banner repeaters seen here at Ealing Broadway, both displaying a clear aspect, as correspondent with their respective signals. Both SN 2092 BR and SN 2091 BR (BR = Banner Repeater) are green, indicating that the paths beyond both SN 2092 and SN 2091 are clear.

Position Signals

1. Subsidiary Signal: used in conjunction with a main signal for calling-on procedures
2. Ground Position Light: typically found on standalone posts with no corresponding main signal
3. Limit of Shunt Signal: a type of ground position light which can display ‘stop’ only

Two examples of ground position signals at Acton sidings, both are displaying a stop aspect. Note however that they are not specifically ‘limit of shunt’ signals, as they both have the capabilities of displaying other aspects.

Permissive Signals

T 1685 is displaying a ‘calling-on’ aspect; the block ahead is occupied, so the signal stays at red, yet the two white lights indicate permission from the signaller to proceed with extreme caution. Additionally, this signal is also fitted with a ‘theatre’ route indicator, telling they driver they’re going into Platform 9 at Reading station in this instance. Note that T 1687 is displaying a clear feathered aspect, while T 1689 is set at danger.