A system of colour light signalling normally employing Red/Green Two
AspectAny valid visual indication of a Signal as displayed to the driver. Stop Signals only (as commonly used on London Underground).
Yellow/green RepeaterAn alternative term for an Indicator (Signal Box). Signals are only provided when required by
inadequate sightingThe process of evaluating the effectiveness of an installed Signal or Element by means of on-site observation of Visibility and Readability. of the stop Signals.