Field Measurements of Capacity and Delay at Unsignalized Intersections

Capacity and delay are key parameters in evaluating intersection operations. Capacity and delay models are available through the 1994 update of the Highway Capacity Manual (HCM), which is commonly used by traffic engineers. These models could, though, provide invalid results when an intersection has unusual geometric or traffic flow conditions. Field measurements are important to verify model results under such circumstances and to ensure the suitability of the recommended intersection control type. Directly measuring capacity and delay can be difficult, though, and videotape data extraction can be time consuming and impractical for most engineers. The authors of this article introduce a practical method for measuring capacity and delay at unsignalized intersections. A model relating average total delay and average queue length based on queuing theory is presented. By conducting field measurements of queue length and volume, the delay is determined. Then, using the delay models of the 1994 HCM update, capacity can be computed.