Work out signal cycle length (webster) instantly with clear inputs, formula shown and shareable results.
Webster's optimum cycle length, (1.5 L + 5) / (1 - Y), minimises total delay. L is the lost time per cycle from start-up and clearance, and Y is the sum of the critical flow to saturation flow ratios across phases. As Y approaches one the cycle length rises steeply, which is why heavily loaded intersections need long cycles and suffer long waits.
Webster optimum cycle
C = (1.5 L + 5) / (1 - Y)
C = (1.5 L + 5) / (1 - Y). Webster's optimum cycle length, (1.5 L + 5) / (1 - Y), minimises total delay.
Up to a point. Longer cycles reduce the proportion of time lost to changeovers but increase delay for every stopped vehicle, and beyond about 120 seconds pedestrian compliance and queue storage become the binding problems.
This calculator takes 2 inputs: Total lost time per cycle, Sum of critical flow ratios. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.