Question

A traffic engineer is trying to design a left turn bay on an EB approach to an intersection. The signal timings for left turns will have ten seconds of "left turn only" green time and 50 seconds of red time each signal cycle. The green time will be sufficient to allow three left turns to be made each signal cycle. An average of 2.5 leftturning vehicles.are expected to approach the intersection each signal cycle. Space is limited, so the engineer wants to minimize the storage capacity of the turn bay, but insufficient capacity will cause the excess vehicles waiting for a green light to block through traffic. If the turn bay has capacity for only three vehicles, what percentage of the time will the through lane adjacent to the left turn bay be blocked?

Answer 1

The through lane adjacent to the left turn bay will be blocked for -20% of the time.

Step-by-step explanation:

To determine the percentage of time that the through lane adjacent to the left turn bay will be blocked, we need to calculate the average number of vehicles waiting in the turn bay. Given that an average of 2.5 left-turning vehicles approach the intersection each signal cycle and the turn bay has a capacity for only 3 vehicles, we know that the turn bay will fill up and block the through lane when there are more than 3 vehicles waiting.

Since the green time allows for 3 left turns to be made each signal cycle, any additional vehicles beyond the capacity of the turn bay will have to wait for the next signal cycle. Therefore, the percentage of time that the through lane will be blocked is equal to the average number of vehicles waiting in the turn bay divided by the total number of left-turning vehicles per signal cycle.

In this case, the percentage of time the through lane will be blocked is (2.5 - 3)/2.5 * 100% = -20%.