What is saturation flow rate in signalized intersection analysis?

What is saturation flow rate in signalized intersection analysis?

• A. The maximum discharge rate from an approach when queues are present and the signal is green.
• B. The minimum discharge rate from an approach when queues are absent.
• C. The average discharge rate over the cycle.
• D. The rate at which vehicles arrive at the intersection.

Answer: (B)

Saturation flow rate is the maximum number of vehicles that can pass a point on an approach when the signal is green and the flow is in a saturated state (the queue ahead has been released and there’s no downstream constraint). It represents the best-possible discharge the lane can achieve under ideal green-time conditions, usually expressed in vehicles per hour per lane. This rate is used to estimate the approach capacity when timing is optimized, and it helps determine whether the arriving demand will be served or whether a queue will build. It’s not about the arrival rate, it’s not the cycle-average discharge, and it’s not a minimum flow when no queue exists.

Saturation flow rate is the maximum number of vehicles that can pass a point on an approach when the signal is green and the flow is in a saturated state (the queue ahead has been released and there’s no downstream constraint). It represents the best-possible discharge the lane can achieve under ideal green-time conditions, usually expressed in vehicles per hour per lane. This rate is used to estimate the approach capacity when timing is optimized, and it helps determine whether the arriving demand will be served or whether a queue will build. It’s not about the arrival rate, it’s not the cycle-average discharge, and it’s not a minimum flow when no queue exists.