Intersection Level of Service and Performance Discrepancies

Aerial photograph of road


The intersection level of service (LOS) method, especially as specified in the US Highway Capacity Manual (HCM), has been around for a long time. It continues to be discussed with various related issues raised by professionals. An example is the ITE eCommunity Group discussion on concerns about perceived discrepancy (or inconsistency) of low delay estimated at a high degree of saturation (volume / capacity, v/c ratio) leading to LOS F in HCM Edition 6. This condition happens in real-life traffic and it is relevant to intersection capacity and performance estimates from analytical models such as HCS, SYNCHRO and SIDRA, or various microsimulation models, although results from different models may differ. The purpose of this paper is to explain how this condition (as well as its opposite condition where high delay can occur at low degree of saturation) can occur and how these conditions relate to other performance variables such as queue length and the number of signal cycles to clear (cycle failures). Level of service methods based on degree of saturation only, delay only, and combined delay and degree of saturation are reviewed. Levels of service for different intersection types are also discussed.


AKÇELIK, R. (2022). Intersection Level of Service and Performance Discrepancies. Paper presented at the 6th International Symposium on Highway Geometric Design, Amsterdam.