The paper describes and analyzes the recurring problem that has appeared in cases where, during the bidding process, the Government has brought to the private investors detailed Engineering Studies, as for example, Definitive Engineering Studies and Feasibility Studies; where after the signing of the Concession Contract, it has been identified that these documents have flaws that need to be corrected so that the execution of road infrastructure, in safe conditions for users, is allowed and also the compliance of service levels required in the Concession Contract. This analysis is done taking into consideration the legal framework for Public Private Partnerships, as well as the principles and rules governing our contractual system; for later have a brief review to the recent publication of the Guidelines for Assigned Risk Contracts for Public - Private Partnerships.