1. Introduction
Public–Private Partnerships (PPPs) are broadly defined as cooperative arrangements between public and private entities that share resources, risks, responsibilities, and rewards to achieve mutual social, economic, or environmental objectives [
1,
2]. This approach serves as a crucial procurement strategy aimed at delivering public assets or services more efficiently through contractual relationships [
3,
4]. In the implementation of PPP projects, a wide variety of types, structures, solutions, and strategies exist [
5]. Based on the extent of private sector involvement, PPP projects can be categorized into several types, including Build–Operate–Transfer (BOT), Design–Build–Finance–Operate (DBFO), Build–Own–Operate–Transfer (BOOT), and Build–Own–Operate (BOO), among others [
1,
6]. The application of these models can vary significantly from country to country. Despite the diverse development of PPP types across different nations, several core elements remain consistent: (1) the involvement of two or more participants, including at least one public sector entity; (2) an enduring and relational partnership; (3) contributions of skills, knowledge, or other resources; (4) shared responsibilities and risks among the participants; and (5) a framework contract that ensures continuity and supports the partnership [
6].
The PPP model is increasingly being adopted worldwide [
7], establishing itself as a pivotal tool for delivering modern, sustainable, and reliable infrastructure and services to a broader population [
8]. It offers numerous advantages to the public and private sectors, as well as other stakeholders [
1]. For instance, public governments can leverage private investment and expertise to provide high-quality facilities and services while sharing risks and responsibilities [
1,
9,
10]. However, unlike straightforward construction projects, PPP projects involve a higher degree of complexity and risk. This complexity arises from the involvement of multiple stakeholders, intricate contract structures, substantial financial investments, extended franchise periods, and cumbersome operational procedures [
1,
11,
12,
13,
14]. In addition to the typical risks associated with general projects, PPP projects exhibit unique characteristics such as diversity, complexity, varying stages, and a dynamic nature [
11].
Lu and Lu define risk as the possibility of adverse outcomes [
15]. Essentially, risk pertains to the consequences of uncertainty [
16]. It typically encompasses two fundamental components: the likelihood of occurrence and the impact on objectives. The consequences of risk can manifest as either opportunities or threats, potentially resulting in a loss of the desired outcome [
17]. In the context of projects, risk is primarily perceived as a potential threat that can lead to project loss if risk events materialize or as a negative factor that may affect the entire project process. Given that every project is exposed to various risks, these can lead to cost overruns, schedule delays, or even project failure [
18]. Risks are inherent to all projects [
19]. In this regard, systematic risk management (RM) is essential for achieving project objectives and ensuring successful outcomes [
1,
8,
20].
Systematic risk management generally involves three main steps: (1) risk identification, which entails recognizing the risks that could potentially affect the project; (2) risk assessment, which involves evaluating both the likelihood of these risks occurring and their potential impact on the project; and (3) risk response, which includes developing strategies to address the identified risks [
1,
17]. In the context of PPP projects, risks and responsibilities are shared between the public sector and private partners [
21]. Consequently, considerable attention must also be given to risk allocation. A fair and reasonable risk allocation scheme facilitates smooth contract negotiations and helps minimize disputes during the concession period [
22].
Given the critical role of risk management in PPP development, research papers on this topic are essential for both researchers and practitioners [
23]. Consequently, a comprehensive literature map that encompasses a wide range of publications on risk management in PPPs is invaluable. It enables a swift and thorough understanding of progress and developments in the field, highlights existing gaps, and identifies potential areas for future research.
2. Literature Review
The rapid expansion of PPP applications, coupled with their unique risk characteristics, has resulted in a significant surge in research interest over the past two decades. This trend has led to a marked increase in the number of published articles, as well as a diversification of research topics, domains, and methodologies [
24].
Le et al. conducted a qualitative analysis of 72 relevant articles using NVivo software, identifying 86 unique risks associated with transportation PPP projects. These risks were classified according to the phase of the project lifecycle in which they are likely to occur [
8]. Akomea-Frimpong et al. performed a systematic analysis of 49 relevant publications retrieved from the Scopus search engine, classifying and assessing the financial risks of PPP projects using techniques such as Monte Carlo simulation (MCS), Net Present Value (NPV), and Internal Rate of Return (IRR). They proposed a series of measures to mitigate the financial risks associated with PPP projects [
25]. Rybnicek et al. analyzed 159 articles published in international journals, identifying eight major risk factors in PPPs. Their analysis provided a cross-sectoral understanding of risks in PPPs and connected the research findings with the current risk management framework [
1].
Tallaki and Bracci conducted a systematic literature review of publications from 1999 to 2018, focusing on risk and risk management in PPPs. They identified six emerging themes: risk definition and types; value for money (VFM) and risk; risk sharing, allocation, and transfer; financial risks; the contractualization and renegotiation of risk; and risk management and governance [
14]. Similarly, Rasheed et al. employed a PRISMA flowchart to provide a comprehensive overview of research concerning risk identification, assessment, and allocation in PPPs from 1996 to 2021. Their findings indicated a shift in focus from overall risk identification and assessment to a more detailed analysis of individual risks [
18].
Research on RM-PPP has been highly productive, yielding significant contributions from each study. However, many existing studies depend on subjective judgments to evaluate the current state and trends in the field, often with a limited scope of literature. To address potential misunderstandings and misinterpretations, an objective review of the scientific literature on PPP is essential for accurately assessing the current state of research and identifying emerging trends [
24]. This study aims to provide an objective review of the literature on PPP by utilizing bibliometric analysis, followed by science mapping methods as outlined by Tijssen and van Raan [
26] and Cobo et al. [
27]. Based on the analysis results, a conceptual model has been developed. Bibliometric analysis offers an objective and quantitative examination of bibliographic material, serving as a valuable tool for organizing information within a specific field. To date, limited reviews have comprehensively linked risk management in PPP across various industries and sectors using a holistic approach that integrates bibliometric analysis, science mapping, and qualitative analysis. This gap represents a significant and underexplored research opportunity, particularly given the ongoing expansion and increasing sophistication of the PPP market across different jurisdictions and sectors [
14,
28].
Developing such a model would be valuable for both the research community and practical applications [
23,
29]. To address this gap, the study focuses on three key objectives:
- (1)
To examine publication trends in RM-PPP through a bibliometric analysis of existing research, focusing on the annual output within the RM-PPP field;
- (2)
To investigate the main contributions of RM-PPP by employing science mapping techniques on a selected literature sample, which includes analyzing and summarizing keywords, leading scholars, countries/regions, institutions, and journal distributions;
- (3)
To develop a conceptual model that combines risk management with the foundational aspects of PPPs, offering insights to guide future RM-PPP research and enhance current practices.
This study is expected to illuminate key research topics and future directions, thereby advancing the development of RM-PPP. Following this section,
Section 3 will present the research methodology, detailing the research design and instruments employed to achieve the research objectives. This will be followed by a comprehensive analysis of the results. Finally, the paper will discuss and conclude with the proposed conceptual model, a summary of research contributions, and suggestions for future research directions.
3. Methodology
The intent of this study is to develop a conceptual model for RM-PPP. To ensure the results of this study are reliable and valid, a bibliometric analysis combined with science mapping was implemented as the foundation for visualizing the up-to-date knowledge on RM-PPP. By minimizing the subjectivity often associated with such studies, bibliometric analysis offers an objective and quantitative examination of bibliographic material, making it a valuable tool for organizing information within a specific field [
30,
31]. Science mapping functions as a bibliometric method for examining and extracting insights from scientific output [
32]. The framework of this study is illustrated in
Figure 1, and the overall flow is divided into four distinct stages.
3.1. Stage 1: Searching and Selecting Articles
In the first stage, relevant articles were searched and selected using electronic databases. In this review, the Scopus engine was chosen as the main source of information to access a wealth of specialized and influential literature. Compared to other databases, such as Web of Science and Google Scholar, Scopus offers the largest collection of peer-reviewed abstracts and citations, and it has published the most articles with high reliability. Moreover, Scopus provides broader coverage than both PubMed and Web of Science. Furthermore, Scopus has been the most commonly used database for previous review articles in the field of project management and risk management in construction [
8,
19,
23,
33].
After determining the database, keywords were developed based on the research aim and questions. In this review, comprehensive keywords used to search for target articles included “public private partnership”, “public-private partnerships”, “build operate transfer”, “build-operate-transfer”, “private finance initiative”, “transfer operate transfer”, “build own operate”, “build own operate transfer”, “build transfer operate”, “reconstruct operate transfer”, “PFI”, “PPP”, and “BOT.” Given that this study aims to discuss the risk issues associated with PPP projects, the term “risk” was also included in the title. Ultimately, a total of 757 articles were retrieved using the specified search terms at this stage. Following the initial sampling, document classification was refined through a primary screening phase. The subject areas were limited to “Business, Management, and Accounting”, “Engineering”, “Social Science”, “Environmental Science”, “Economics, Econometrics, and Finance”, “Decision Sciences”, and “Energy”. Only English-language journal articles were included in this study, while reviews, books, editorials, and conference proceedings were excluded. At the conclusion of this process, 422 records were selected for further analysis.
3.2. Stage 2: Visual Inspection
Despite the search criteria implemented in Stage 1, some irrelevant publications may still appear in the results—those that match the keywords but do not address risk issues in PPP projects. Therefore, in this stage, the filtering process was refined by closely examining the titles and abstracts of the selected papers. All duplicates were removed, and irrelevant articles were excluded. This process resulted in a total of 416 papers containing high-quality content for subsequent analysis. The final distribution of papers related to RM-PPP in the Scopus database is shown in
Figure 2. It is evident that the development of risk management research in PPPs can be divided into three distinct stages. The first is the initial stage from 1990 to 2001. During this period, research related to RM-PPP was relatively sparse, which can be attributed to the fact that the concept of PPP was just emerging, with its implementation limited to a few developed countries and regions. Research on PPP was in its early exploratory phase. The second stage is the growth phase from 2002 to 2016. In this period, there was a general upward trend in RM-PPP research, although the development was not entirely stable. For instance, in 2004, only two papers related to risk management were published, with noticeable declines in publication numbers between 2005–2007 and 2012–2014. The third stage is the exponential growth phase from 2017 to the present. Since 2017, the growth in research has been nearly exponential, indicating a significant increase in academic interest in RM-PPP. This trend suggests that RM-PPP is an important and evolving research area that continues to garner attention and is likely to see further development. These findings highlight the increasing academic awareness of risk issues in the PPP field and underscore the ongoing importance of RM-PPP as a research topic.
3.3. Stage 3: Bibliometric Analysis and Visualization
To analyze and provide a science mapping of the selected articles, VOSviewer software was employed to visualize the current state of risk management in PPP projects. Developed by Leiden University in the Netherlands, VOSviewer is a specialized computer program designed for creating, displaying, and investigating bibliometric networks [
34,
35]. This software is capable of analyzing various types of textual data and generating structured maps in several formats, including label view, density view, cluster density view, and scatter view [
36,
37]. VOSviewer is particularly useful for examining a large volume of items in detail, allowing for comprehensive analysis and visualization of bibliometric data [
37].
In recent years, VOSviewer has gained widespread recognition used as a scientometric analysis tool due to its capacity to deliver more objective and reliable analyses [
38,
39]. It is also applied in the field of project management [
3,
38]. In this research, VOSviewer was utilized to map the collaboration networks of keywords, authors, countries or regions, affiliations, and journal co-citations. Following the bibliometric analysis and science mapping, a qualitative review was conducted to summarize the current research focus areas in risk management related to PPPs. This process provided a comprehensive understanding of the primary research trends within the PPP domain and facilitated the identification of prevalent issues and gaps in the field.
3.4. Stage 4: Synthesizing
Finally, by synthesizing the results of the bibliometric and qualitative analyses, a conceptual model is proposed to help guide future research on the RM-PPP topic.
5. Discussion and Conclusions
This study employs a scientometric approach to analyze the existing literature on risk management in PPPs. The research is dedicated to (1) examining publication trends in RM-PPP through a bibliometric analysis of existing research, focusing on the annual output within the RM-PPP field; (2) investigating the main contributions in RM-PPP by employing science mapping techniques on a selected literature sample, which includes analyzing and summarizing keywords, leading scholars, countries/regions, institutions, and journal distributions; and (3) developing a conceptual model that combines risk management with the foundational aspects of PPPs, offering insights to guide future RM-PPP research and enhance current practices.
Based on the four research stages illustrated in
Figure 1, this study employed a comprehensive approach that integrates bibliometric analysis, science mapping, and qualitative analysis across 416 journal papers collected from the Scopus database, published between 1990 and September 2023. Science mapping was used to examine keywords, identify the most productive researchers, and analyze the contributions of countries or regions, journals, and institutions that have significantly impacted RM-PPP. Unlike other methods, the scientometric analysis employed in this study minimizes arbitrariness and avoids the artificial bias that can arise from handling large volumes of bibliometric data [
24,
85]. This is due to the fact that scientometric analysis is a quantitative research technique that facilitates the visualization of extensive bibliometric data. Recently, this scientific approach has been applied to the PPP field [
3,
38]. Following the science mapping, a further qualitative analysis of the selected RM-PPP literature provided insights into the research topics, perspectives, and methodologies applied in recent years.
An examination of annual publication trends reveals that RM-PPP-based studies have experienced a steady increase over the past several decades, indicating three distinct development stages. An analysis of the keywords, leading authors, institutions, and countries or regions highlights the following:
- (1)
The co-occurrence analysis of research keywords within the RM-PPP literature identifies six main clusters that represent the primary distribution of research in current RM-PPP studies. These clusters are (1) risk allocation; (2) risk management; (3) risk assessment; (4) risk, risk ranking, risk perception, and project performance; (5) models, frameworks, and China; and (6) construction projects, project management, factor analysis, AHP, and decision-making. These clusters illustrate the current distribution of research efforts in RM-PPP, highlighting major topics of interest, methodologies employed, regions studied, and the interconnections among various aspects of risk management in PPP projects;
- (2)
Chan A. P. C. and the Hong Kong Polytechnic University are the most productive author and institution in the field of PPP, particularly in the domain of risk management [
3]. The consistent productivity in both domains indicates a strong and focused research interest in risk management within PPP projects;
- (3)
China leads in research on PPP, demonstrating the highest output in terms of the number of published articles, citations, and total link strength. This suggests that a significant portion of research in the realm of RM-PPP is concentrated on projects within China or incorporates Chinese case studies;
- (4)
The categorization of research into various topics, including risk support, identification, assessment, allocation, response, and integrated management, underscores the complexity of risks in PPP projects. Each category addresses a unique aspect of risk management, highlighting the inadequacy of a singular approach. Therefore, a comprehensive strategy is essential, beginning with risk identification and evaluation, advancing through allocation and mitigation, and ultimately culminating in an integrated risk management framework;
- (5)
Examining various research perspectives on RM-PPP reveals the complexity, diversity, and interdependence of projects and stakeholders. This multidimensional approach facilitates the development of more comprehensive and sustainable PPP risk management strategies, ensuring a balanced consideration of interests and contributing to the successful implementation of projects;
- (6)
In recent years, there has been an increasing emphasis on the application of quantitative approaches, such as the Analytic Hierarchy Process (AHP) and various models in risk management. This trend reflects the complexity and multifaceted nature of risks, necessitating sophisticated and systematic methods for effective analysis and management.
Risk management is a critical factor in the success of PPP projects [
86], spanning the entire project lifecycle, from initiation and planning to implementation and operation. Effective risk management not only facilitates the identification and mitigation of potential challenges but also fosters smooth collaboration between the public and private sectors, ultimately achieving the project’s objectives. Based on the analysis and considerations presented, a conceptual model has been developed (see
Figure 10) to enhance the understanding of risk management in PPP projects. This model initiates a dynamic, cyclical process that includes risk identification, assessment, allocation, and control, followed by the ongoing identification of emerging risk factors as the project progresses. This iterative approach is essential, as risks evolve over time as the project advances through its various phases [
1]. Furthermore, the model acknowledges that the risks associated with PPP projects are highly specific to each individual project [
41]. Variations in project types, geographic locations, and local conditions often lead to significant differences in the nature and impact of risks. As such, an effective risk management strategy must be customized to the specific characteristics of the PPP project, incorporating detailed project information and contextual factors into the risk management process. Summing up, the model derived from this research integrates both the general risk management process and the specific attributes of PPP projects. By providing a structured approach that combines these elements, the model aims to improve risk management outcomes by ensuring that all participants have a clear understanding of the critical risks and considerations at each stage of the project.
The rapid development and expansion of PPP projects worldwide have introduced new demands for effective risk management. Given the critical role of risk management in both academic research and the practical application of PPP procurement, this study conducted a comprehensive four-stage literature review. Utilizing VOSviewer software and bibliometric analysis, the study provides an in-depth examination of the current state and future directions for research on PPP risk management. Recent years have seen a significant increase in research related to PPP risk management, yielding substantial findings. Effective and well-structured risk management is essential for the successful implementation of PPP projects, as it enhances the likelihood of achieving favorable outcomes. Therefore, it is imperative for scholars to investigate significant risks while considering the specific constraints of each project. Consequently, the systematic study of risk management is expected to remain a central focus in PPP research.
The contributions of this research are mainly twofold. First, in terms of practical contributions, this study offers valuable insights for practitioners involved in PPP projects, particularly in the field of risk management. The conceptual model developed in this research provides a structured and dynamic framework that can be used by project managers, government agencies, and private sector stakeholders to better identify, assess, allocate, and mitigate risks throughout the project lifecycle. By incorporating both general and context-specific risk factors, the model enables practitioners to tailor their risk management strategies according to the unique characteristics of each project. Furthermore, the use of scientometric analysis highlights trends and best practices in risk management, which can guide decision-makers in adopting more effective and data-driven approaches to managing risks in PPP projects. Secondly, in terms of theoretical contributions, this study presents a systematic overview of Public–Private Partnership (PPP) risk management by analyzing factors such as publication trends, key researchers, and active institutions. This analysis aids scholars in developing a holistic understanding of the knowledge landscape and the key players in the field, thereby advancing theoretical understanding. By integrating scientometric and qualitative analyses, the study investigates major research topics, perspectives, and innovative methods in PPP risk management. This multidimensional approach enriches existing theories, highlighting the diversity and complexity of research in the field and establishing a foundation for future theoretical advancements. Furthermore, the study proposes a conceptual model for risk management in PPP projects grounded in a comprehensive literature review. This model offers a structured theoretical framework, providing new insights for both academic research and practical application. It serves as a guide for scholars in developing new theories and methodologies within the field. Collectively, this study establishes a robust knowledge foundation for both scholars and practitioners, serving as a valuable resource for newcomers and a reference for experienced professionals seeking to deepen their expertise. This foundational knowledge equips both groups to navigate the complexities of risk management in PPP projects and apply their understanding in both practical and research settings.
Nevertheless, this review is not without its limitations. The authors acknowledge certain constraints in the literature review methodology. First, the literature sample is confined to English-language peer-reviewed journals sourced from the Scopus database. As a result, some articles on PPP risk management may have been overlooked, either because relevant keywords did not appear in the titles or because the papers were not indexed in Scopus. Additionally, despite a rigorous systematic literature review, cognitive biases cannot be entirely eliminated, potentially leading to limitations in the analysis and deviations in the identification of research themes. The current study aims to develop a conceptual model that integrates the general risk management process with the specific characteristics of PPP projects. However, due to the extensive number of publications reviewed, this research provides only a broad overview of risk management in PPP projects. For a more detailed understanding, future research should focus on conducting in-depth and specific analyses of risk management within PPPs to uncover more nuanced insights and detailed findings in this area.