Webster Optimum Signal Cycle Length
Hardsignalswebster
A signalised intersection has a total lost time of 12 seconds per cycle and a sum of critical flow ratios of 0.75. Using Webster's formula, the optimum cycle length is most nearly:
- A46 seconds
- B69 seconds
- C92 seconds
- D115 seconds
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Answer: C. 92 seconds
Webster's optimum cycle is C₀ = (1.5L + 5)/(1 − Y) = [1.5(12) + 5]/(1 − 0.75) = 23/0.25 = 92 seconds. As Y approaches 1.0 the cycle length grows without bound, which is the formula's way of saying the intersection is at capacity.
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