Public-Private Partnerships (PPPs) are used by governments to develop road projects that, generally, require high investments. However, uncertainty about future traffic levels represents the main cause of road project failures, which can be mitigated through government traffic guarantees and make them more attractive to private investors. These guarantees place a financial burden on the government s budget that can significantly influence the deficit and, thus, the government s risk and opportunities. This thesis carried out three different studies that address the importance of guarantees in road public-private partnership contracts by properly estimating these guarantees and their impact on project risk through Real Options Theory (ROT). The first analyzes the government traffic guarantee levels in the projects, limiting government exposure, and maintaining the benefits for the private investor. Then, the second studies focus on the potential government s contingent liabilities caused by traffic guarantees and, for this, is analyzed the case of the Salvador–Itaparica Bridge system project and discusses the publicly available government reports on the project with our results. The last study cares about designing an adequate traffic guarantee mechanism for PPP contracts in Road Projects and, for this, we propose a model to determine the traffic guarantee s optimal level that creates favorable conditions for the development of the projects. This Thesis contributes to a better understanding of guarantee mechanisms for private partners and the importance of adequately pricing the contingent government liabilities in infrastructure projects, revealing that a properly designed guarantee mechanism can minimize the government s contingent liabilities and provides adequate guarantees to the private partners. Moreover, also provides a methodology that assists policymakers in designing infrastructure PPP projects and understanding the contingent claims and fiscal costs involved.