What does the Peak Hour Factor (PHF) measure?

The Peak Hour Factor (PHF) is a critical measure used in traffic engineering to evaluate the variation in traffic flow during peak hours. Specifically, it quantifies how much the traffic volume during the peak hour fluctuates compared to the average volume within that hour. The PHF is calculated using the formula:

[ \text{PHF} = \frac{\text{(Hourly Volume)}^2}{\text{(Sum of 15-Minute Volumes)} \times 4} ]

This metric helps to better understand traffic conditions and manage roadway capacity. A higher PHF indicates that traffic flow is more consistent throughout the peak hour, while a lower PHF suggests significant fluctuations, with some 15-minute periods seeing much higher or lower volumes.

Understanding this factor aids traffic engineers in designing efficient roadways, optimizing signal timing, and planning for congestion mitigation strategies. It does not directly relate to the daily overall traffic volume, average vehicle speeds, or roadway capacity, which are more focused on other analytical parameters.