International experience shows that creating large infrastructure objects (as a rule, with state participation) is often accompanied by significant cost overruns. Importance of this issue is especially high due to responsibility for the use of public resources. The article reviews most recognized methods of the project risks evaluation that play a key role in assessing the total cost of large and long-term projects. Approaches of international organizations, official documents of selected developed countries and requirements for Russian infrastructure projects with state funding are compared. Particular attention is paid to a comprehensive quantitative risk evaluation, which is not sufficiently represented in the Russian official methodology, based on Monte-Carlo simulation modelling. The study considers some practical aspects of applying this method for conditional cost estimation. As an illustration, a model calculation of the impact of risks on the indicators of one of the latest PPP infrastructure projects (CRR-1) is given.