Design a traffic signal for the following right angled intersection
- Major street = 12 m (4 lanes)
- Minor street = 6 m (2 lanes)
- The peak hour volumes in each direction are indicated accordingly
Solution: Assuming that the average pedestrian speed = 1.2 m/s
Pedestrian clear time along the major road = 12 / 1.2 = 10 seconds
Peak green time = 10 + 7 = 17 seconds
Pedestrian reaction time = 17 seconds
Therefore, minimum green time for vehicle on minor street = 17 seconds
Pedestrian clearance time for minor street = 6 / 1.2 = 5 seconds
Pedestrian green time for vehicle on major street approach = 12 seconds
Critical lane volume on major street = 660 / 2 = 330 vehicles/hour/lane
Critical lane volume on minor street = 180 / 1 = 180 vehicles/hour/lane
Green time on major street approach = (330/180)*17 = 31.16 seconds
~ 32 seconds
Adding initial amber and clearance amber of 2 seconds each
Minimum cycle length = (2 + 17 + 2) + (2 + 32 + 2) = 57 seconds Adopting the next multiple of 5 we have the maximum cycle length as 60 seconds
Add 3 seconds (2 seconds for major street approach and 1 second for minor street approach = ratio of volume of traffic on major street to volume of traffic on minor street)
The results for the signal timing (in seconds) are tabulated below:
Signal Initial Green Clearance Red Cycle
timing Amber Amber length
Major street 2 34 2 22 60
Minor street 2 18 2 38 60
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