In addition to the spatial relationship as described there is also a temporal relationship governing the traffic lights.
This sequence used in Hong Kong is illustrated in Table I.
The duration of the and signals are normally fixed to 3 s in each iteration while the duration of the and signals may be varied manually or automatically.
The argument for utilizing this temporal relationship in the detection is that outdoor environment
is hostile.
For instance any sudden change in the ambient light level may affect the brightness of the lights especially the green
light and may introduce ambiguity.
Therefore tracking the light sequence would probably provide a more stable and robust solution.