Traffic-speed pavement structural evaluation to enhance mobility and road safety
Authors: Elseifi Mostafa 
Published: November 2013

Pavement evaluation is performed to assess the functional and structural conditions of roadways for routine monitoring in order to select proper corrective actions. Functional condition is related to the roughness and ride quality of a highway section. Structural condition deals with a pavement's ability to withstand traffic loads and environmental conditions, which can be measured by determining material properties, layer thicknesses, and surface deflections. The evaluation of pavement structural capacity and integrity is an important component of Pavement Management System (PMS) to assist in the selection of suitable maintenance and rehabilitation strategies. However, testing of in-service pavements is a major challenge due to traffic delays, lane closure, and safety of the travelling public and the highway workers. Traffic-speed pavement evaluation methods offer the potential to cost-effectively characterize the structural capacity of the road network without major delays or safety risks during measurements. These evaluation devices include innovative technologies such as continuous deflection testing including the Rolling Wheel Deflectometer (RWD) that collect data at traffic speeds that can be used to evaluate pavement structures. This study describes a detailed field evaluation of the RWD system in Louisiana in which pavement sites representing a wide array of pavement conditions were tested. The RWD consists of semitrailer applying a standard load on the pavement structure by means of a regular dual-tire assembly over the rear single axle. The RWD measures wheel deflections at the pavement surface by means of a spatially coincident method, which compares the profiles of the surface in both undeflected and deflected states. As the RWD travels on top of the pavement, triangulation lasers mounted are used to measure surface deflections. In this study, field measurements were used to assess the repeatability of RWD measurements, the effect of truck speeds, and to study the relationship between RWD and falling weight deflectometer (FWD) deflection measurements and pavement conditions. Based on the results of the experimental program, it was determined that the repeatability of RWD measurements was acceptable with an average coefficient of variation at all test speeds of 15 percent. In addition, the influence of the testing speed on the measured deflections was minimal. This study also developed and validated a direct and simple model for determining the pavement structural number (SN) using RWD deflection data. To develop this model, the relationship between the average RWD surface deflection and the peak FWD deflection was investigated. The developed model correlates a pavement's SN to two RWD-measured properties (average RWD deflection and RWD index). Results showed a good agreement between SN calculations obtained from FWD and RWD deflection testing. While the developed model is independent of the pavement thickness and layer properties, it provides promising results as an indicator of structural integrity of the pavement structure at the network level. The fitting statistics support the use of the proposed model as a screening tool for identifying structurally deficient pavements at the network level.