In a sequential series of phases, how many phases are served at a time?

Answer: C — One

In a sequential series of phases, a single phase is served at a time. This means that during a given cycle, only one traffic movement is granted the right of way while other movements are halted, ensuring that traffic flow is managed in an orderly way. This method is designed to minimize the potential for conflicts between different directions of traffic, enhancing safety and efficiency at intersections. In many traffic signal systems, phases are typically organized such that each one corresponds to specific movements of vehicles and pedestrians. By serving only one phase at a time, it allows for clear signaling and helps to manage traffic effectively. This approach is foundational for traffic signal control, as it follows the principles of safe traffic operations. While other choices suggest multiple phases or movements could be active at once, serving more than one phase simultaneously could lead to confusion among drivers and an increased risk of accidents at intersections. Thus, serving one phase at a time is the standard and correct approach.