The risk concept provides a means of incorporating some degree of certainty into the process to ensure that the outcomes of the process will provide acceptable levels of service until the end of the intended design life. In pavement design and evaluation, the risk concept is applicable for the input parameters with a high degree of uncertainty and that have an impact on the final outcome of the design process. The 2004 AUSTROADS Pavement Design Guide emphasized that much of the misunderstanding of pavement design, and resulting pavement failures over the past 20 years has been associated with uncertainty and resulting lack of reliability in design. Pavement structural evaluation and rehabilitation designs are highly dependent on the in-situ layer properties. Pavement layer thickness is an essential input in backcalculation analysis performed on measured surface deflections by Falling Weight Deflectometer (FWD) survey. Inaccurate layer thickness information may lead to significant errors in the backcalculated layer moduli and hence in the rehabilitation design. Since the pavement layer thickness has some degree of variability, it is important to consider this variability in the backcalculation analysis and rehabilitation design. In this paper, a risk-based pavement evaluation methodology will be introduced to account for the variability of pavement layer thickness through integration of FWD and GPR data. It is be demonstrated that the proposed methodology can help RCAs more accurately assess the pavement structural condition of road network with more confidence. The proposed procedure is also applicable in project level for the construction acceptance testing of new or rehabilitation pavement.