Verification of network-level pavement roughness measurements

In 1997 the Ministry of Transportation of Ontario (MTO), Ontario, Canada, switched to international roughness index (IRI) measurements as an indicator of network-level pavement roughness within its pavement management system. Measurement of pavement roughness or ride quality in terms of IRI can be performed with different measuring devices. However, the individual measurements for the same pavement section may vary significantly because of the use of different measuring devices, different longitudinal profiles, and different measuring speeds. Recent evidence obtained by MTO indicates that the longitudinal profile measurements provided by different measuring devices contain systematic differences that range from 0.1 to 1.0 m/km. Such differences in IRIs cause significant concerns for agencies that contract out collection of network-level roughness measurements on a yearly basis. Through the process of verification and comparison of longitudinal profile measurements obtained with different profilers, MTO has gained insight into the functional relationships and factors that affect profile measurements in terms of precision and bias. The verification techniques used to obtain normalized, reproducible, and time-stable IRI measurements for IRIs supplied by different IRI providers are described. Preliminary findings and statistical analyses of IRI values measured on a verification circuit. which is composed of 12 sections with four different pavement types, are provided. In addition, the results of analyses of the various IRI measurements and their impacts on network-level pavement serviceability are discussed.