- 2016 Taylor & Francis Group, London. Pavement design is a probabilistic process as it involves many random variables. Through the incorporation of reliability, pavement design methods consider input parameters variabilities effect on pavement performance. Load and Resistance Factor Design (LRFD) is a typical example of reliability-based design procedure. In LRFD, a set of partial safety factors are developed by modelling input parameters variabilities with representative average conditions. This paper evaluates the impact input parameters variabilities have on estimated target reliability in the case when actual variabilities are different from assumed conditions. This was achieved by evaluating a field pavement section with various combinations of input parameters variabilities. The optimized section for a given target reliability was achieved through the mechanics-based LRFD procedure and the actual reliabilities of the various cases were obtained using a methodology that uses response surface approach and first order reliability method (FORM). The results have shown that the level of input parameters variabilities used affect the target reliability considerably.