Six projects from six countries wereselected as the cases for detailed analysis in this study.They are from Argentina, Botswana, India, Kenya, Lao PDR andParaguay, representing a wide range of geographicaldistribution. Also, the extent of the effect of economicdownturn which these countries experienced ranges a widevariety. In an economic downturn, uncertainties increasewith many inputs of road projects Cost Benefit Analysis(CBA), including fuel prices, levels of demand, investmentcosts and maintenance availability. Also, importantparameters of project evaluation such as discount rate andvalue of time need to be more carefully scrutinized.Therefore, it is very important for the developing countriesto have good understanding about the effects of thevariability of these inputs/parameters on project viabilityand the ranking of road investments. It is a role of thedeveloping agencies to conduct a systematic analysis ofthese effects and disseminate the findings and knowledgeobtained. The objective of the study is to obtain insightsregarding the effects of varying inputs and parameters onthe viability of road projects through case studies usingHighway Development and Management Model (HDM-4), thereby tofacilitate the formulation and implementation of roadprojects that increase the welfare of the society under theenvironment of increased uncertainty in an economicdownturn. The results of the study will be summarized in atransport note as a discrete knowledge product anddisseminated among various stakeholders including developingagencies staff, government officials and donor communities.To assess the effects of increased uncertainty with inputsof cost benefit analysis on the economic viability of roadprojects, this study first investigated the range ofvariability of the inputs for the six selectedprojects/countries. It was found that the variability rangesdiffer by country reflecting the degree of decrease intransport demand and relative change in factor prices due toeconomic downturn.