Calculate the volume-to-capacity percentage, traffic volume or capacity, or compare travel-time indices. Use demand and capacity for the same direction and period; the capacity presets are screening estimates.

Use traffic demand and capacity for the same direction, road segment and time period.

Related Calculators

Congestion Index Formula

The following formula is used to calculate the Congestion Index.

CI = (V / C) × 100

Variables:

  • CI is the Congestion Index (%) (the volume-to-capacity ratio expressed as a percent)
  • V is the volume of traffic (vehicles per hour)
  • C is the capacity of the road (vehicles per hour)

To calculate the Congestion Index, divide the volume of traffic by the capacity of the road. Multiply the result by 100 to convert it to a percentage. This expresses traffic demand as a percentage of the stated road capacity (V/C%). Values above 100% indicate demand exceeds that capacity. Use demand rather than bottleneck-constrained measured throughput when assessing oversaturation. Note: some organizations use the term “congestion index” for different, travel-time-based measures; this page’s CI is strictly a capacity-utilization measure.

What is a Congestion Index?

On this page, a Congestion Index is the volume-to-capacity ratio (V/C) expressed as a percentage. It is a simple indicator of how close a road segment (typically for a specific direction and time period) is operating relative to its stated capacity.

How to Calculate Congestion Index?

The following steps outline how to calculate the Congestion Index.

  1. First, determine the volume of traffic (V) in vehicles per hour.
  2. Next, determine the capacity of the road (C) in vehicles per hour.
  3. Select Congestion index (V/C%) and use CI = (V / C) * 100. The other modes solve for traffic volume or capacity, compare travel times, or provide a clearly limited capacity screening estimate.
  4. Finally, interpret the result (for this definition, 100% means demand equals the stated capacity; values above 100% indicate oversaturation).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

volume of traffic (V) = 1800 vehicles per hour

capacity of the road (C) = 2000 vehicles per hour

CI = (V / C) × 100 = (1800 / 2000) × 100 = 90%. This means the road is operating at about 90% of its stated capacity.