When does a traffic signal cycle begin?

Answer: C — When all phases have completed one full sequence

A traffic signal cycle is defined as the complete sequence of phases that a traffic signal follows from the beginning of one phase until it returns to the same phase, effectively covering all indications (red, yellow, green) for each direction. This means that the cycle begins when the first phase is activated and continues through to the point where all phases have completed their sequence and the signal returns to the starting phase. Understanding this, the correct answer indicates that a cycle begins when all phases have completed one full sequence. It encompasses the entire operational rhythm of the signal, so defining the start based solely on when one phase turns green or displays an initial time does not provide a comprehensive perspective on the entire operation of the signal. For example, if one only considers when the first green light activates, it neglects the fundamental aspect that a traffic signal operates with multiple phases that must be completed to make a cycle coherent. Each phase must be transitioned through for traffic management, thus ensuring that all movements are accounted for before the cycle resets. This perspective helps traffic signal technicians understand not just individual light changes but the overall traffic flow management facilitated by the complete cycle of signals.