What does Peak Hour Factor (PHF) indicate in traffic counts?

What does Peak Hour Factor (PHF) indicate in traffic counts?

• A. How evenly traffic is distributed within the hour; higher PHF means more uniform flow.
• B. The maximum average speed during peak hour.
• C. The percentage of time the signal is green during the hour.
• D. The time headway between every two vehicles.

Answer: (A)

Peak Hour Factor is about how traffic is spread out within the hour. It’s defined as the hourly volume divided by four times the largest 15-minute volume observed in that hour. If the traffic is evenly distributed, the busiest 15-minute period would be about a quarter of the hourly total, giving a PHF close to 1. If most of the traffic occurs in a short subinterval, the largest 15-minute block is larger relative to the hour, and PHF drops below 1. So a higher PHF means more uniform flow throughout the hour, while a lower PHF indicates a more peaked, uneven distribution. This concept is not about speed, signal timing, or headways; it specifically captures the distribution of flow over the hour. For example, with an hourly volume of 1000 vehicles, a busiest 15-minute block of 250 yields PHF = 1, while a busiest 15-minute block of 400 yields PHF = 1000 / (4*400) = 0.625.

Peak Hour Factor is about how traffic is spread out within the hour. It’s defined as the hourly volume divided by four times the largest 15-minute volume observed in that hour. If the traffic is evenly distributed, the busiest 15-minute period would be about a quarter of the hourly total, giving a PHF close to 1. If most of the traffic occurs in a short subinterval, the largest 15-minute block is larger relative to the hour, and PHF drops below 1. So a higher PHF means more uniform flow throughout the hour, while a lower PHF indicates a more peaked, uneven distribution. This concept is not about speed, signal timing, or headways; it specifically captures the distribution of flow over the hour. For example, with an hourly volume of 1000 vehicles, a busiest 15-minute block of 250 yields PHF = 1, while a busiest 15-minute block of 400 yields PHF = 1000 / (4*400) = 0.625.