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Peak Hour Factor Calculator

Work out peak hour factor instantly with clear inputs, formula shown and shareable results.

About Peak Hour Factor Calculator

The peak hour factor is hourly volume divided by four times the busiest fifteen minute count. It measures how evenly demand is spread: a factor of 1.0 means perfectly uniform flow, while 0.8 means the busiest quarter hour carries a quarter more than its share. Capacity analysis uses the flow rate, four times the fifteen minute count, not the hourly volume.

Formulas

Peak hour factor

PHF = hourly volume / (4 x highest 15 minute volume)

Design flow rate

Flow rate = hourly volume / PHF = 4 x peak 15 minute volume

Worked example

With the default values below, Peak Hour Factor Calculator returns Peak hour factor of 0.8182. Change any input above and every figure here is recalculated in your browser.

Inputs used

Volume in the peak hourminimum 1 veh
1,800 veh
Volume in the busiest fifteen minutesminimum 1 veh
550 veh

Results

Peak hour factor
0.8182
Design flow rate
2,200 veh/h
Share of the hour in the peak quarter
30.56% %
Assessment
Pronounced peaking — design on the flow rate not the hourly volume

Step by step

  1. 1Values used
  2. 2Peak hour factor
  3. 3Design flow rate
  4. 4Peak hour factor= 0.8182
  5. 5Design flow rate= 2,200 veh/h
  6. 6Share of the hour in the peak quarter= 30.56 %
  7. 7Assessment= Pronounced peaking — design on the flow rate not the hourly volume

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Peak Hour Factor figure worked out?

PHF = hourly volume / (4 x highest 15 minute volume). The peak hour factor is hourly volume divided by four times the busiest fifteen minute count.

Why design on fifteen minutes rather than the hour?

Because queues form during the peak quarter and do not clear. Designing on the hourly average leaves the intersection oversaturated for fifteen minutes every peak.

What values do I need to enter?

This calculator takes 2 inputs: Volume in the peak hour, Volume in the busiest fifteen minutes. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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