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An isolated three-phase traffic signal is designed by Webster’s method. The critical flow ratios for three phases are 0.20, 0.30 and 0.25 respectively, and lost time per phase is 4 seconds. The optimum cycle length (in seconds) is _________.
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- 90 to 95
- 80 to 85
- 40 to 60
- 80 to 90
Correct Option: A
Time lost in cycle, L = 4 × 3 = 12 seconds
Sum of flow, y = y1 + y2 + y3
= 0.2 + 0.3 + 0.25 = 0.75
| Optimum cycle length, Co = | ||
| 1 - y |
| = | = 92 s | |
| 1 - 0.75 |
