Intersection capacity describes the traffic an intersection can accommodate under defined demand, geometry, control, and analysis conditions.
Definition
Intersection capacity describes how an intersection accommodates traffic under specified conditions. An analysis may consider volumes, geometry, traffic control, signal timing, and pedestrian activity, along with the selected method and performance measures. Inputs and assumptions shape the result, and agencies or projects may use different methods and criteria. Firms may scope work around particular movements, time periods, alternatives, or reporting needs, so owners should clarify intended use. Capacity analysis is an estimate for defined conditions, not a complete measure of safety, community impact, or future performance under every scenario. It is not the same as a turning movement count, although count data can be an input. The results support evaluation and discussion of alternatives, while project decisions depend on broader criteria and context. The ASCE professional resource provides general context for civil transportation engineering.
How owners use it
- Set the analysis period, demand inputs, geometry, control assumptions, and performance measures in the scope.
- Review data and method limitations before comparing alternatives or discussing results with a client.
- Use analysis results to inform project conversations alongside safety, access, and other relevant considerations.
- Example: If an approach handles 600 vehicles per hour against a stated capacity of 750, the volume-to-capacity ratio is 600 ÷ 750 = 0.8.
