The analysis of the large infrastructure projects effects reveals frequent errors in the intensity of traffic flows or investment costs estimation, which can jeopardize the established feasibility of the project. This reflects the importance of ex-post analyzes because they provide valuable information on the fulfillment of project goals, ie they are useful for the purpose of efficiency monitoring and cost-benefit analysis (CBA) improvement. A feasibility study for the construction of the second carriageway of the E75 freeway, on the section from Novi Sad to Belgrade, was done in 2003, and the results of a detailed traffic and economic analysis showed the absolute economic feasibility of this project. ex-post analysis of key factors enabled the identification of realized effects and the identification of all deviations, both in time dynamics and in economic indicators of costs/benefits. The results of the first conducted ex-post analysis of infrastructure projects in Serbia showed that the Mean Percentage Error (MPE) in the traffic forecast is -16.42%, and that investment costs are exceeded by 9.3%. The obtained internal rate of return (IRR) is less than 33% to 50% depending on the observed variant, but even the most critical value of 7.03% showed that the project was economically feasible.