**6. Conclusions**

Since the introduction of cooperation under PPP, there are many successful projects as well as failures. Only approximately 30% of PPP projects in Poland are implemented [13]. The development of PPP literature has followed the growing experience in public–private cooperation. Currently, scholars tend to stress that the motives standing behind PPP can be highly polarized and PPP can no longer be perceived as just a solution to acquire additional capital that could satisfy everyone in an equal way. Due to these reasons, this research tries to offer a descriptive stance and to identify the main stakeholders in PPPs, examine their engagemen<sup>t</sup> in PPP, and define stakeholders' success.

The article was based on stakeholder theory, which indicates that there is more than one approach to project managemen<sup>t</sup> and puts into light the importance of meeting stakeholder needs [52]. The conducted literature review reveals that the problem of joint cooperation between the public and private sector still requires stakeholders centered analysis. At the same time, growing research interest in project success and more specifically the perception of success by different stakeholder groups can be observed. This research approach combined two main ideas, which are the perception of success in the public and private sector, and stakeholder engagement. A conceptual benefit–engagement model for a new interpretation of stakeholders' identification and classification in PPP projects was proposed, which was then verified via a selected case study of a unique infrastructure investment taken from Cracow in Poland—a country characterized by development success in recent years.

The findings identified apparent discrepancies in the perception of PPP success between main PPP stakeholder groups, which can be classified into four groups (research question 1). Stakeholder Type I and Type II are the most influential in the PPP project. They include two focal stakeholders, who are sponsors and a grantor. Generally, lenders and bond investors are grouped in Type III. Type I and III evaluate the project generally based on its profitability. Type IV are stakeholders who perceive success in the broadest context.

They are stakeholders focused externally without a direct financial interest in the project. Type IV evaluates the PPP according to socio-economic criteria, long-term impact, and creating future opportunities.

This benefit–engagement classification, including the polarized goals of different stakeholder groups, justifies evaluating PPP project success as a whole. Through the use of the benefit–engagement model, public and private partners will be able to be more aware of who the stakeholders are and what the relations between them in terms of engagemen<sup>t</sup> and interest (research question 2) are. This will lead to more informed decisions, precision in their choice of project, and help in successful PPP delivery.

The criteria of benefits and engagemen<sup>t</sup> show how different stakeholder groups perceive PPP success (research question 3). The model distinguishes financial and nonfinancial benefits, which can be gained in the short and the long-term, and which became criteria for success evaluation of the sustainability of the project. The second dimension of the conceptual model is engagement. Engagement incorporates the attributes of power and urgency. Power refers to the ability to influence the definition of the project [30], and access to critical resources [43]. The urgency is defined in the model after Schepper et al. [10] as a degree to which stakeholders claim to call for immediate attention. This benefit– engagemen<sup>t</sup> model can be a tool for early and joint stakeholder managemen<sup>t</sup> supporting individual motivation and attitude towards success, especially about, but not limited to, focal stakeholders.

The Underground Car Park case study confirms that a proper allocation of responsibilities between directly engaged stakeholders can cause uninterrupted cooperation with other indirectly engaged groups focused on two different types of benefits (financial or non-financial). The grantor—Cracow City—represented by the City Hall at the early stage of the project addressed the needs of the local community and other local organizations, whereas, during the operational stage, the stress was laid on addressing stakeholders focused on financial benefits. During that stage, the leading role was assigned to the project company. However, the City Hall still played an important role because it is responsible for shaping transport policy in the City. As a takeaway for practice, the research proves complex relations between different stakeholders and the diversity of PPs in terms of place and time. It is a prime issue especially for economies under transition, which are still gaining knowledge in the area of the managemen<sup>t</sup> of and for their various stakeholders [53]. This research proves that only a holistic approach to PPP can lead to sustainable development, as only then does it cover economic, social, and environmental criteria. The success of the PPP project as a whole is then achieved when all stakeholders receive their benefits, which would simultaneously confirm the project's sustainability. Finally, the study proposes a background for further research on PPP success and important stakeholders groups of PPPs and their understanding of PPP success. By addressing these aims, a greater understanding of how PPP success dimensions can be measured and managed can be achieved.

The main limitation of the study arose from the broader need for empirical validation of the presented conceptual model. Although observations are made over a selected case study within a limited period, and the context of the analysis and stakeholder perception may change according to the dynamics of stakeholders, the research has a particular strength relating to its prospective dimension. It offers compelling evidence that stakeholder managemen<sup>t</sup> is difficult under the best of circumstances, and becomes even more challenging in the presence of varying interests. Future research could consider characteristics of specific country circumstances and specifications of different types of PPP projects as the need to adopt a more stakeholder-oriented perspective in project managemen<sup>t</sup> results from many participants involved, but also from different PPP forms, contracts, and country traditions.

**Author Contributions:** J.W. 55% and A.W.-F. 45%: Conceptualization, J.W. and A.W.-F.; Formal analysis, J.W. and A.W.-F.; Funding acquisition, J.W.; Investigation, J.W. and A.W.-F.; Methodology, J.W. and A.W.-F.; Project administration, J.W. and A.W.-F.; Resources, J.W. and A.W.-F.; Supervision, J.W. and A.W.-F.; Visualization, J.W. and A.W.-F.; Writing—original draft, J.W. and A.W.-F.; Writingreview & editing, J.W. and A.W.-F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was co-funded by Cracow University of Economics (agreement no. 5/EEN/ 2020/POT).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
