Peak Hour Factor | Transportation Engineering - Civil Engineering (CE) PDF Download

The peak-hour factor, often abbreviated as PHF, is a metric used in transportation planning and traffic engineering to describe the variation in traffic flow during the peak hour compared to the average flow over a period of time, typically a day. It's calculated as the ratio of the peak-hour traffic volume to the average daily traffic volume.

This factor is essential for designing transportation infrastructure, such as roads and highways, to ensure they can accommodate peak-hour traffic demand without becoming congested or overwhelmed. Understanding the peak-hour factor helps planners determine the appropriate capacity and design features necessary to maintain efficient traffic flow during peak periods.

The peak hour factor (PHF) serves as a comparison between the traffic volume observed during the busiest 15 minutes within the peak hour and the total volume witnessed throughout the entire peak hour. It essentially quantifies the consistency of traffic volume during the peak hour, offering insights into how uniform or varied the traffic flow is within that period.

PHF = (total hourly volume) / [(peak 15-minute volume within the hour x 4)]
= V / (VPeak x 4)
0 < PHF >= 1

A PHF of 1 implies a consistent traffic volume across all 15-minute intervals within the peak hour, indicating a uniform traffic flow throughout that hour. Conversely, lower PHF values suggest more variability in traffic flows, signaling potential spikes in traffic volume specifically during the peak 15-minute interval. This variability highlights moments of higher congestion or irregular traffic patterns within the peak hour.

Here's an example of how to solve for the peak-hour factor using some hypothetical numbers:

Let's say you have traffic volume data for a certain road for a typical weekday:

• Average Daily Traffic (ADT): 10,000 vehicles per day
• Peak Hour Traffic Volume: 1,500 vehicles during the peak hour

To find the peak-hour factor:

Peak Hour Factor (PHF) = Peak Hour Traffic Volume / Average Daily Traffic

Substituting the given values:

PHF = 1,500 vehicles / 10,000 vehicles
PHF = 0.15

So, in this case, the peak-hour factor is 0.15. This means that during the peak hour, traffic volume is 15% of the average daily traffic volume.