The Federal Highway Administration (FHWA) requires each state to obtain the International Roughness Indices (IRI) of its road network and enter them into its Highway Performance Monitoring System. The reported IRI for road segments are compared to the national standards set by the FHWA. Basedon FHWA’s IRI standards for all road classes, an IRI of 170 in/mi or lessis deemed “acceptable”, and 95 in/mi or less is categorized as “good”. IRI values correlate with the roughness of the pavement and the quality of the ride experienced by occupants of vehicles. The extent of variations of the observed IRI values from the national standards are used, in part, to identify road segments that need to be included in repair or maintenanceprograms. There is concern that the pure values of the IRI are sometimes in conflict with the ride quality perceived by vehicle occupants in dense urban jurisdictions. In response to that problem, some states are establishing IRI thresholds that involve ride quality perceived by resident motorists. The problem appears to be more acute in urban areas where the dominant road classifications are arterials and local streets, and where the public’s tolerance for pavement roughness is relatively higher because of low operating speeds. This paper presents an exploratory investigation of appropriate IRI thresholds for roads in the District of Columbia using the opinion of citizens who rode in vehicles on selected road segments, IRI survey data, and the District’s ride quality specifications for newly constructed pavements.
Abstract