Variation of Pavement Smoothness Between Adjacent Lanes: Implications for Performance-Based Contracting

There is a need to understand how pavement smoothness varies over space and time and with other environmental factors. Information from a large set of international roughness index (IRI) field data together with traffic and pavement design and age data is used to consider IRI variation across the lanes of multilane highways and freeways in the state of Connecticut. The objective is to determine to what extent IRI varies over all lanes through time in order to consider the amount of field data that will have to be collected for departments of transportation to adequately measure or predict pavement rideability for newer performance-based contracting agreements, particularly those involving contractor warranties. Results indicate that on the basis of IRI, small average roughness differences exist between adjacent lanes. IRI values are highest in the outer right lanes. Lateral differences are relatively consistent and random but small in magnitude. No strong effects could be found between pavement age, composition, or traffic loading and IRI. However, some preliminary evidence suggests that the influence of these factors may also vary by lane. These results have implications for future research as well as the logistics of pavement monitoring by agencies for warranty-based contract payments. First, the difference in IRI between lanes is small and consistent (0.1 to 0.2) when averaged over longer sections, and therefore it is not necessary to repeat measurements for all lanes along longer projects or whole routes. Second, the variation in these field IRI measurements is unpredictable, especially over smaller spatial areas, suggesting that IRI data should be collected in all lanes when shorter projects are being considered.