A pelican crossing $($derived from PELICON, PEdestrian LIght CONtrolled crossing$)$ is a pedestrian

crossing in which standard RED$-$YELLOW$-$GREEN traffic lights face oncoming traffic, and illuminated

WALK$/$DON$$T WALK pictograms face pedestrians. The traffic lights remain at GREEN $($and the pictogram at DON$$T WALK$)$ until a pedestrian wishing to cross presses a button. This illuminates a WAIT

light at the button, and eventually causes the traffic light to change: first to YELLOW, and then to RED

at the same time as illuminating the WALK pictogram. Whilst the WALK pictogram is lit, a BEEP

sounds $($replacing the WAIT light$).$ Eventually, the WALK pictogram begins to flash $($and the BEEP

ceases$)$ at the same time as the traffic light changes to a flashing YELLOW, after which the traffic light

changes to GREEN at the same time as illuminating the DON$$T WALK pictogram.

A summary of the actions, and the resulting states of the traffic light, pedestrian light, and signal, are

presented in the following table: