In this paper, we have considered the key features of the mechanism of public-private partnerships in St. Petersburg. We have discussed the stages of implementing PPP projects in St. Petersburg using the mechanism of project financing, in particular, organizing a specialized project-financing company (SPFC). We have developed a PPP project for constructing a network of multi-level surface parkings in the territory of Vasileostrovsky District of St. Petersburg, justifying the implementation of this project by calculating the deficit of parking places in the given area. We have calculated the lack of parking spaces based on an estimate of the number of available parking spaces in the district, in particular, in each municipality, as well as by the average number of cars among residents of municipal districts. The investment attractiveness of each of the objects planned for construction was evaluated within the framework of the developed project. The effectiveness of the developed project was assessed by the method of net present value, used to calculate the total net profitability of the entire project life cycle for each parking lot separately. A model for project appraisal has been developed using linear programming methods as a universal mechanism for evaluating the effectiveness of implementing PPP projects. The essence of this model is finding the optimal distribution of resources between projects with a deficit of initial capital investments and maximizing aggregate NPV. The developed model for evaluating investment projects was used to select the best parking lots for building depending on the total amount of available resources. In total, seven variants of initial investment in implementing this project were considered. Implementing PPP projects by applying the SPFC procedure can help increase the revenue base of budgets of public partners from the income gained by providing paid services to the population (dividends on concession bonds issued as part of the investment project), as well as tax revenues from enterprises created in the process of project implementation. The model used in this study for evaluating the effectiveness of a PPP project is universal and can be applied both in evaluating projects implemented based on the principles of PPP, and in commerce for assessing the feasibility of project implementation.