Traffic Signal Design MCQ with answer and solution

Concept

Webster's Optimum Signal Cycle Length

Formula

C0 = (1.5L + 5) / (1 - Y)

Step-by-step solution

1. Identify given parameters: Total lost time (L) = 20 s and critical flow ratio sum (Y) = 0.50 2. Calculate the numerator: (1.5 \* 20) + 5 = 35 3. Calculate the denominator: 1 - 0.50 = 0.50 4. Divide numerator by denominator: 35 / 0.50 = 70 seconds

Explanation

According to Webster's formula, the optimum signal cycle length is given by C0 = (1.5L + 5) / (1 - Y), where L is the total lost time and Y is the sum of the flow ratios. Substituting the given values: C0 = (1.5 × 20 + 5) / (1 - 0.50) = (30 + 5) / 0.50 = 35 / 0.50 = 70 seconds. Therefore, option B (70) is correct.

Common mistake

Students often forget to add 5 in the numerator of Webster's formula, calculating C0 = (1.5L) / (1 - Y) = (1.5 × 20) / 0.50 = 60/0.50 = 60, or incorrectly forgetting the (1 - Y) term in the denominator and calculating C0 = 1.5L + 5 = 35 seconds.