What is the primary purpose of timing plans for signals?

• A. To define cycle length only
• B. To adjust cycle timing based on detectors
• C. To specify phase sequences, green splits, and cycle lengths to optimize flow
• D. To measure air quality

Answer: (C)

Timing plans for signals are like a timetable for how an intersection should behave over a cycle. They define the order in which movements are served (phase sequence), how long each movement is allowed to go green (green splits), and the total duration of one complete cycle (cycle length). This combination lets engineers coordinate signals along a corridor so vehicles and platoons can progress smoothly from one intersection to the next, reducing stops, delays, and conflicting movements while maintaining safety. The phase sequence ensures the necessary movements—through, left-turns, pedestrians—are arranged in a safe, efficient order. Green splits allocate the available green time to each movement in proportion to demand, so busier movements get more time and overall flow is improved. The cycle length sets how often the plan repeats, influencing how quickly signals can react to changing traffic patterns and maintain progression. While detectors and actuated control can adjust timings in response to real-time conditions, the primary purpose of a timing plan is to specify the planned sequence, durations, and cycle length to optimize traffic flow. Measuring air quality is not part of what timing plans address.