Service Volumes for Functional Classification

Highway agencies adopting or exploring functional classification will find advantages in using the level of service concept of the 1965 Highway Capacity Manual in establishing service volumes for functional systems. Functional classification is the grouping of roads and streets into connected systems based on the functions they serve. Each system has its own design standards to provide the speed, directness, mobility, and access desired. The service volumes selected for design purposes are one of the most important features of the standards since they influence mobility and the general level of service provided motorists. A lower level of service will generally result in increased service volumes which may reduce the number of lanes required to accommodate design traffic. The selection of levels of service and the service volumes are the prerogative of the highway agency. This paper presents an approach by the Illinois Division of Highways based on its system needs and foreseeable funding.