Environmental, social and governance assessment criteria for public-private partnership projects: a systematic review

The shift from Corporate Social Responsibility (CSR) to a more encompassing framework known as Environmental, Social, and Governance (ESG) is believed to have been spurred by the increasing concern for climate change and social equity in the US, as highlighted by the global COVID-19 pandemic (Chao and Farrier, 2021; Andrey, 2023). ESG factors include environmental impacts, social responsibility, and corporate governance practices, whereas CSR encompasses the integration of social, environmental, and economic concerns into business practices to create better practices and improve society (Husnah et al., 2023). Studies have indicated how ESG has been a primary concern in recent times. Evidence suggests that 97 financial institutions in 37 countries have committed to the Equator Principles assessing environmental and social risk in projects and emphasising the quest for responsible investment (Husnah et al., 2023; Robinson and McIntosh, 2022).

ESG issues are critical for public-private investors when investing in infrastructure assets, and therefore, are considered to be similar to any other investment risk AMP Capital (2021) is of the view that ESG considerations in infrastructure PPP's aim to create greater wealth and better investment decisions and opportunities. ESG considerations in PPP investments involves mitigating the risk connected with the physical features of the investment and managing the contractual arrangements and the performances of counterparties responsible for operational risks of the project (AMP Capital, 2021). The growing interest and shift towards ESG practices by businesses is not just limited to selected projects, companies and countries but it is becoming a global trend. It is anticipated that ESG practices will continue to play a significant role in shaping and influencing investor behaviour and business practices. While efforts have been made to promote individual contributions to sustainability performance, low awareness and understanding of sustainability goals still exist within PPP investment projects (Leal Filho et al., 2019). From theoretical lenses such as the stakeholder, institutional, legitimacy, agency and voluntary discourse theories, this study identifies strategic ESG criteria for PPP investment project. Exploring specific ESG criteria that affects the sustainability performance of PPP projects can help unearth how future projects can be sustainable (Ma et al., 2021). It is purported that implementing ESG in PPP projects can be instrumental in delivering sustainable projects and enhancing ESG dimensions (Amalia et al., 2023; Chao and Farrier, 2021). This therefore presents a research attention that focuses on unearthing ESG assessment criteria for PPP projects and how they contribute to UN sustainability goals (Kharlamov, 2023). In addition, investors require a broadened understanding of ESG impacts on value and investment performance (AMP Capital, 2021), making it crucial to identify ESG assessment criteria for a better investment project decision making.

Amidst the ambiguity about the ESG assessment criteria because of the peculiarities of industry practices, the present study aims to unearth ESG assessment criteria and to determine which of them are critical for PPP projects. In as much as there are some studies that have highlighted PPPs actions towards ESG and sustainability performance, there is still a paucity of research on ESG assessment criteria of PPP projects (Amalia et al., 2023; Kharlamov, 2023; Robinson and McIntosh, 2022). The development of an ESG metric for a sector typically takes several years because it must go through several iterative revisions to ensure the standards are comprehensive and relevant (GRI, 2023). The purpose of this study is to clarify findings and criticisms of the extant literature on the lack of existing ESG assessment criteria for PPP projects by first conducting a systematic review to identify key ESG assessment criteria for PPP projects. This study systematically identified, appraised, and synthesized existing evidence of ESG indicators of construction and infrastructure projects. Towards the end of this review the study addresses the research gaps by answering the questions:

1. What are the ESG assessment criteria of PPP projects?

2. What are the effects of these criteria on project sustainability?

This study's findings inform investors and policy makers of PPP infrastructure projects regarding the ESG materiality that should be considered when assessing PPP sustainability performance. The study is among a few to undertake a review into ESG assessment criteria for PPP infrastructure projects.

This study is guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol. This is a comprehensive systematic review protocol used to minimize the risk of bias and increase the scientific validity of the study findings. This critical appraisal method was used to select the papers involved in the main study to establish quality and relevance of the research studies. This process involved evaluating the methodological rigor, validity, and reliability of the studies, as well as assessing the alignment of the research with the study's objectives and the overall contribution to the field. Authors read, assessed, and ranked the selected papers for inclusion and full-text reading following the PRISMA guideline. A detailed review process is illustrated in Figure 1 (PRISMA flow chart). This study presents a review that encompasses a wide range of research papers and organisational reports, providing a thorough understanding of the various ESG criteria identified for PPP investment projects in these documents. Publication quality was assessed by authors based on the inclusion and exclusion criteria and the relevance of these documents to the research question. First, selected articles were identified through Scopus database to provide a high level of rigorousness. Second, article selection was conducted using the inclusion criteria to select relevant papers that responded to the research objective. Third, two authors independently evaluated the reliability of articles using descriptive analysis framework and resolved discrepancies associated with topics, methods and research impact (Ke et al., 2025). Authors followed the PRISMA guideline to minimize the methodological errors and ensured trustworthiness and relevance of the papers, included in this article (Akomea-Frimpong et al., 2023). For instance, the authors ensured that the documents from grey literature were from established organizations. These documents were included to ensure that the risk of biasing results from only academic literature and regional bias were taken care of (Pappas and Irene, 2011). The selected papers were subjected to thorough content analysis.

Scopus database was searched in February 2025 for studies reporting on PPP in critical infrastructure, construction, private and public projects with the aim of identifying global ESG assessment criteria in PPP investment projects. The Scopus database was chosen as it is identified as one of the leading databases that houses management, construction and engineering research articles. The study used the following search terms:

TITLE-ABS-KEY (“Environmental, Social, and Governance” OR “ESG” OR “social sustainability” OR “Corporate Social Responsibility” OR “Environmental Sustainability” OR “Governance Sustainability”) AND TITLE-ABS-KEY (“build operate transfer” OR “build, own and operate” OR “build, own, operate and Transfer” OR “build, transfer and operate” OR “Build-Operate-Transfer” OR “construction projects” OR “design, build, finance and operate ” OR “Infrastructure Investment” OR “Infrastructure Project” OR “infrastructure projects” OR “Mega ? project” OR “Megaproject” OR “operation and maintenance” OR “PPP infrastructure project” OR “PPP Projects” OR “PPPs” OR “private business” OR “Private Finance Initiative” OR “private investments” OR “private projects” OR “Public Facility” OR “public ? private*” OR “Public Works”).

In the beginning of assessment of the documents retrieved, the following inclusion criteria were used. (1) The publication language was restricted to English. (2) Articles relevant to the keywords were selected. (3) Research studies that had clear focus on ESG, social sustainability, corporate social responsibility, environmental sustainability, and governance sustainability for PPP projects addressing the research question were selected. (4) Also, considering that ESG became a topical issue after covid-19 crisis when global responsible investors began to strengthen the case for responsible investment (UNPRI, 2020), recently published studies were highly relevant for this study. (5) Peer-reviewed conference proceedings, literature reviews and articles were considered. To avoid publication bias, capture emerging evidence of ESG practices for PPP, and broaden the evidentiary base beyond peer-reviewed journals, the study included grey literature (Boadi et al., 2025). Grey literature search was conducted using Google search engine to include relevant government documents, and standards that are focused on PPP projects. Google Scholar is without word builders, the study specifically used the search terms: “Environmental, social and governance or sustainability practices of mega projects, PPP, construction, and infrastructure projects” to identify reports from investors, government and institutions (AMP Capital, 2021; AFED, 2011; ICLG, 2024; UNPRI, 2020). The first ten pages in Google Scholar which included 100 documents were screened by authors where 8 documents were identified and included in the review (Boadu et al., 2023).

The search code generated three hundred and eighty-seven (387) documents from Scopus database. Eight (8) additional records were identified from the grey literature search. In total, three hundred and ninety-five (395) documents were retrieved for further examination. Further screening of the titles and abstracts of the 395 documents were done to identify the relevant studies for ESG and PPP practice. Fifty-three (53) documents were finally selected for full reading. After full reading six (6) articles were excluded, and forty-seven (47) documents were maintained for content analysis.

The study extracted relevant metadata from the selected documents, including information on ESG assessment criteria or sustainability indicators mentioned in the selected studies. A data summary sheet was developed to record global criteria mentioned for Environmental, Social and Governance. Thirty-nine (39) research articles and eight (8) documents from organisational reports were discovered.

First, the study recorded issues of sustainability considerations in each document by content analyses, and these issues were placed under ESG. Second, the study subjectively recorded the total number of occurrences for each criterion based on how often it is being mentioned by studies and reports for further quantitative investigation. The dominant practices emerging from literature are emphasized as the foundational ESG practices for PPP project sustainability. Finally, authors computed weights, ranks (for overall criteria and within a grouping) and created relative importance index (RII) for prioritizing identified criteria presented in Table 2. Below are the mathematical formulas used.

Weight for each criterion is (⁠$μi)=∑i=1n(Ci)n$⁠, where n denotes the total number of occurrences of a criterion for a group, $Ci$ is the frequency of occurrence given to each criterion by a document (either 0 or 1). For instance, to determine the weight of how PPP project affect air quality, it is the sum of the number of times of occurrence of the criterion over the number of occurrences within the group (Environmental indicator). The weights for each criterion were then ranked both for the overall criteria and within a grouping.

Also, a relative importance index is computed as $RII=∑i=1n(Ci)a*N$ where, $a$ is the highest weight (i.e. 1 in this case was recorded in the article), and N is the total number of documents (47). This presents the level of relevance that current studies place on each criterion.

Based on the selected studies, the research has been able to identify 46 ESG criteria that can be used to assess PPP investment projects. These criteria have been grouped under Environmental, Social and Governance as shown in Table 1 with the number of occurrences. Based on the number of criteria identified, frequency for each indicator were calculated. Table 2 shows that out of the 46 criteria, 13 (28.26%) constitute Environmental assessment criteria, whereas the Social criteria consist of 17 (36.96%), and the Governance criteria is 16 (34.78%). In the following paragraphs, the study presents a discussion of the top 5 criteria to each assessment indicator.

Environmental practices of projects are essential to enhance a projects sustainability thereby contributing to profitability, community development and eradicating extreme poverty. Positive environmental indicators ensure project continuity, project acceptance, increased stakeholder trust and environmental justice (Chao and Farrier, 2021). The environmental ESG indicator emphasizes the need for evaluating the long-term impact of infrastructure development projects on ecosystems and natural resources (Kahangirwe, 2012). This indicator considers factors such as compliance with environmental legislation, integrated urban development policy, and strategic environmental assessment.

PPP projects should consider factors such as the conservation of biodiversity, the preservation of natural habitats, the reduction of greenhouse gas emissions, and the sustainable use of natural resources to be environmentally sustainable. The result of the study showed that environmental indicators constituted 28.26% of ESG assessment criteria of PPP projects. Therefore, environmental practices are key determinants of PPP's sustainability performance. Chao and Farrier (2021) purport that the private company contribution in the PPP project ensures that renewable energy infrastructure, remediation and waste reduction are aligned in the project. Below are the environmental assessment criteria identified from the content analysis of data.

This environmental criterion is identified as the top rank (1) among the identified criteria in this study. This assertion was based on weight of 0.17 from the environmental indicator in Table 2. It is also evident that 40% research emphasis is placed on this criterion as an environmental measure of PPP projects. Protecting and conserving biodiversity and habitats and sustainably managing living natural resources is a gold standard that makes sustainable finance. According to the World Bank Environmental and Social Framework, all projects that are supported through investment project financing must adhere to the Standard 6, which is identified to be a key determinant of PPPs environmental ESG indicator (WBG, 2022). PPPs activities are susceptible to biodiversity loss due to the reason that projects have immediate impact on plants, and animals within their natural habitat. This study finding is in tandem with previous studies whose finding showed that environmental principles of PPP infrastructure constitute biodiversity conservation, deforestation, and deterioration of protected nature territories (Mishenina and Jaroslav, 2022). Harmonizing PPP projects with the local natural setting will ensure that the environment is safe.

This environmental criterion is ranked second (2nd) among the identified criteria. This assertion was based on weight of 0.14 from the environmental indicator in Table 2. The table also shows that 34% of the selected studies place emphasis on this criterion as an environmental measure of PPP projects. The objective of green solid waste management is to handle waste in a way that addresses public health and environmental concerns while promoting resource conservation through waste material reuse and recycling (AFED, 2011). Concerning this criterion, the study found that green solid waste management in PPP projects contributes about 14% to the environmental indicator of PPP investment project. Study by The National Treasury and Economic Planning (2024) revealed that green solid waste management in infrastructure projects is also seen as a practice that ensures waste material recovery that foster green jobs. PPP projects must ensure that there is the formalization of local waste collectors to participate in the project. Thus, PPP projects invest in waste reduction, reuse, and recovery. Having a comprehensive plan that comply to waste monitoring, recycling, and reuse by engaging private sector actors in the circular economy waste management is an environmental concern in PPP projects.

This environmental criterion is ranked third (3rd) among the identified criteria. A weight of 0.13 was recorded by this criterion within the environmental indicator in Table 2. The table indicates that 30% of the selected studies place emphasis on this criterion as an environmental measure of PPP projects. Decision on energy use and resource consumption is an increasing stakeholder demand criteria in ESG matters of PPP project. Chao and Farrier (2021) indicated that private companies have contributed greatly to the area of renewable energy infrastructure in PPP projects. Efficiently managing energy consumption in a PPP project is crucial for enhancing the environment, supporting the local economy, and delivering positive outcomes for citizens. This perspective is underscored by a weight of 0.13 assigned to this criterion.

This criterion is also shown in Table 2 to be a relevant environmental indicator of PPP projects. Land use is material in PPP projects during construction works. To minimise potential adverse impacts on land use, projects involving petroleum hydrocarbons, heavy metals, pesticides, solvents, and runoff should be carefully managed. This ensures that the use of these materials does not lead to groundwater contamination, increased erosion, ecological imbalances, or reduced soil fertility and productivity. During the construction stage, projects can also cause landslides, affect slope stability and contribute to land pollution (Radzi et al., 2024). Additionally, Rosasco and Sdino (2023) emphasize that project impacts on the surrounding environment must be sustainable, considering both the landscape and local flora and fauna.

The environmental performance indicators used to assess project sustainability primarily focus on environmental compliance. Air pollution has emerged as a global environmental concern. According to Table 2, PPP projects contribute to air quality impairment due to activities such as exhaust emissions from construction machinery, transport vehicles, and dust generated during excavations. Agyekum et al. (2022) showed that construction activities on air quality are the second most significant environmental indicator of construction related activities. Air quality surveys can be undertaken to assess the adequacy of these controls.

PPPs are often used to deliver “social” or “community” infrastructure assets and facilities. Ensuring a favourable community perception is crucial for the ongoing success of a public-private partnership project and is commonly known as a “social license to operate” (AMP Capital, 2021). Assessing and managing the social risks and impact of PPP projects contributes to the standards 2, 4, 5, 7, and 8 Environmental and Social Frameworks that ensure sustainable finance (WBG, 2022). Similarly, with regards to formal legal license to operate, the idea of “social license to operate” is necessary to ensure that the social impact of projects can be communicated and understood. In PPP projects, ensuring the overall well-being of individuals in the community and worker safety and health are keen sustainable practices of the projects. Projects being able to accommodate the sense of health and wellness of inhabitants promotes the acceptance of safe environment for work. The study established that the social sustainability indicator of PPP projects constitutes 36.96% of the ESG assessment criteria. It is indicative from this study that the social criteria of PPP projects are the most critical sustainability indicator. For a PPP project to be sustainable, it must create an enabling future society by empowering the local community and improving people's well-being and quality of life. The findings highlight social sustainability attributes in these projects, emphasizing stakeholder involvement, community development, diversity, equality, inclusivity, and access, among other factors.

Concerning this criterion, articles that were reviewed for this SLR found that PPP's worker health and safety contribute to 13% of the social ESG criteria of PPP investment projects. This social criterion is the first and highly ranked (1) among the identified criteria for PPP projects. Also, this criterion is considered the topmost among all ESG criteria of PPP projects. A weight of 0.13 was recorded by this criterion within the social indicator, whereas 59% of the selected studies place emphasis on this criterion as an ESG measure of PPP projects. It is evident that worker health and safety issues are identified as the criterion that is highly relevant amongst the ESG assessment criteria for PPP projects; this assertion was based on an RII value of 0.59. It can be inferred that the workers' health and safety issues are key license for PPP projects to operate. This study result aligns with a report by MSCI (2023) that showed that workforce health and safety are among the most social material factors of ESG criteria for the Engineering and Construction sector.

Evidence in literature regarding PPP tendering and award through stakeholder engagement shows that for the social sustainability practices of PPP, stakeholder engagement is key. In the identified social ESG criteria of PPP projects, PPP tendering and award through stakeholder engagement constitutes 11% of PPP projects, the second highest criterion of social indicator of PPP projects. As purported by Amalia et al. (2023), stakeholder engagement in PPP projects identified at the first stage of PPP implementation must ensure that all issues that surround PPP contracts have been outlined through stakeholder engagement. Doing this, tender documents and agreements that includes all commitments to manage the project at the project implementation phase in the last stage are communicated. It is shown that this criterion (RII = 0.51) is second highest ESG material factor of PPP projects.

Impact of projects on the community or individuals living within the project siting affect them. This criterion is also shown to significantly impact PPP projects social contribution. Understanding the vulnerabilities of affected individuals and community and improving their socioeconomic status will ensure sustainable environment. Empowering the individuals or groups by fostering local business development, and improved community development and economic contribution will contribute to project acceptance. Research has shown that key social sustainability indicators for public-private partnership (PPP) projects include economic contributions such as employment opportunities, local investment creation, materials production, and enhanced local infrastructure capacity (Gurmu et al., 2022).

PPPs can serve as a useful tool for governments to promote diversity, equality, inclusivity and access, both in the project's intended outputs and inputs, thus, impacts throughout the various stages of a PPPs lifecycle. A significant determinant of PPPs social sustainability indicator is how projects ensure diversity, equality, inclusivity, and access. PPP projects should therefore assess whether its contract and activities provide gender-sensitive facilities and access for people of all walks of life. As part of private equity ESG strategy, Alfonso-Ercan (2020) indicates that having a formal corporate policy that outlines a firm's approach and vision regarding diversity and inclusion of employees and other stakeholders is crucial. Also, a report by Marsh Mclennan (2022) on how construction projects can succeed together with their ESG showed that diversity and social inclusion are key in determining a sustainable project.

Another social criterion is that projects provide employment opportunities and sound work ethics during the construction and project operation. PPP projects have an ethical and a legal duty to provide a workplace free of harassment of all types to its workers. Ensuring that PPP employment contracts adhere to various employment practices that are applicable by laws and regulations; a study by Hendiani and Bagherpour (2019) has unearthed employment opportunities as a social sustainability dimension of construction projects. It is believed that hiring employers who establish impartial practices are drivers of high social sustainability practices. Lindell and Olander (2019) believe that another social consideration in the procurement of PPP projects is to promote increased employment, promoting decent working conditions and complying with the principle of equal treatment including the equal pay for work of equal value.

Considering how PPP projects manage their activities to ensure sustainable projects success is necessary. An essential governance option for PPP projects is to incorporate sustainability considerations into their operations. Another governance option is to prioritise quality aspects in procurement decisions over price (Hueskes et al., 2017). Finding the balance between legitimate revenue generation, social interest and potential environmental impact is relevant in the day-to-day dealings of infrastructure projects. Studies have identified that the governance aspect of PPP ESG practices is a significant focal point of a project. It is shown to be the second highest indicator that has several determinants. These criteria contribute 34.78% of the ESG indicators of PPP projects. Thus, highlighting the significance of accountability, legitimacy, and transparency in governance, as well as corporate governance, ethics, anti-corruption measures, and cybersecurity in infrastructure projects. The five material governance criteria for PPP projects are presented below.

In the aspect of governance, studies have considered PPP governance whose concern is about reaching the commercial and financial close of a project as a key determinant of governance sustainability indicator of PPP projects. An RII value of 0.255 was the basis of this assertion. This governance criterion is the first and highly ranked (1) among the identified governance criteria for PPP projects. Thus, PPP projects should offer guidance on achieving a smooth delivery process while avoiding common pitfalls, without being overly prescriptive. The project should specify the roles of evaluators, decision-makers, and contract approvers. Guidance on the extent of negotiations permitted to reach commercial close and getting to financial close should be addressed. Studies have shown that this criterion involves finding the balance between legitimate revenue generation, social interest, and potential environmental impact, which is relevant in the day-to-day dealings of PPP projects (Kharlamov, 2023; Hosny et al., 2022).

Evidence from literature ranked this criterion as the second (2) highly ranked criterion of PPP governance ESG indicators. It is believed that businesses that cultivate a profound understanding of their supply and value chains beyond traditional organisational boundaries are the ones poised for success. This criterion also places emphasis on how investing in PPPs supply chain management leads to ensuring that materials are available when and where needed, enabling the project to progress smoothly and on schedule. It is believed that PPP projects may suffer supply chain disruptions that will impose on renegotiation of prices and delivery deadlines. It is therefore required that PPP projects prioritise the whole procurement process, from the choice of project until the end of the execution (InfraPPP and WAPP, 2023).

In the process of identifying, preventing, mitigating and accounting for how projects address the problem under investigation, it is good to follow due diligence. The tender document and drafted PPP contracts should be looked at thoroughly by possible interested parties, they should be educated on what the tendering and the contract entails. This is one of the critical governance criteria which needs to be considered right from the planning, construction, and the operation phases of the project. This ensures that all project stakeholders are clear about the project outputs, responsibilities, and risk allocation. Thus, projects bidders should review PPP tender documents and draft contracts in detail. Goel et al. (2020) indicates that explicit considerations of project feasibility at this stage ensure the successful implementation of sustainable and socially responsible practices in the project.

Demonstrating and adhering to national laws, responsible business practice, anti-corruption throughout the project lifecycle prevents the negative impact that stem from it. Another significant governance criterion is PPP project promoting integrity throughout the project lifecycle. Within this governance criteria, projects should ensure the existence of strategies that promote accountability, transparency, and integrity. These strategies apply both internally and externally, involving interactions with customers, suppliers, and third-party agents. A decline in integrity is a potential risk of project failure. it is believed that perceived mismanagement of funds at the expense of local interest can trigger conflicts; therefore, projects should ensure that operations are assessed for risks related to corruption, and actions are taken about corruption related incidents (GRI, 2023).

Another criterion that is a pillar of PPP ESG assessment is issues about the data security and cyber security. To determine whether PPP contract projects establish trust and have the difficult discussions about cybercrime-related issues like encryption, data access, cloud servers and privacy protection, it must place important role on how data security and cybersecurity impact the project. ICLG (2024) indicates that project companies should assess their corporate security and business continuity plans, focusing on enhancing data and cyber protection as well as building resilient systems.

The conceptual framework presented is focused on ESG materiality assessment for public-private partnership (PPP) projects. This encompass environmental, social, and governance factors that are important to PPP projects for sustainability assessment. Figure 2 is a three -layer framework that puts assessment criteria of PPP projects into a sustainability assessment structure. The environmental criteria evaluate the project's impact on the natural environment, including resource consumption, emissions, and waste management. The social criteria focus on the projects impact on the community, labour practices, human rights, and stakeholder engagement. Finally, the governance criteria assess the projects management structure, transparency, accountability, and ethical business practices. The framework represents granular performance indicators of the ESG assessment criteria that flows upwards to a single holistic score leading to sustainable decision-making. The framework present factors that are considered impactful by research studies to PPP stakeholders. The identified criteria for each ESG construct are interrelated and intra-related. The study outcome informs current view of relative materiality of PPP ESG factors from research perspectives. The environmental criteria ensures that projects minimise negative environmental impacts and promote resource efficiency, contributing to long-term environmental sustainability, the social criteria places emphasis on community engagement, labour rights, and social inclusivity, ensuring that projects benefit local communities and address social challenges. By considering these interconnected ESG assessment criteria, PPP projects can be designed and managed in a manner that not only delivers economic benefits but also contributes to environmental preservation, social well-being, and ethical governance, aligning with the principles of sustainable development and responsible business conduct. It is therefore hypothesised that PPPs project sustainability is a function of the project related factors identified in this study for environmental social, and governance. This framework serves as an overarching reference for facility implementers ESG standards that ensures a broader application of ESG principles in PPP projects.

The study results showed that evaluating the long-term impact of infrastructure development projects on ecosystems, green solid waste reduction and natural resource conservation is necessary. Attributes critical to social sustainability in PPP projects were identified to be prioritizing worker health and safety, effective PPP tendering and awarding involving stakeholder engagement. The governance aspect of PPP sustainability practices also places emphasis on significant defined plan for reaching commercial and financial close of a project, using improved supply chain planning process, and ensuring due diligence with tender documents and drafted PPP contracts. Critical criteria unearthed demonstrate the quest for meeting stakeholder demands, addressing asymmetric information issues, and the influence of good governance practice for sustainable delivery of project. These are well supported by the legitimacy and voluntary discourse theory that forms the basis of this investigation. The hypotheses for PPPs project sustainability have been developed.

The study establishes a theoretical checklist of forty-six (46) PPP ESG assessment criteria for PPP investment decision making. The various criteria identified detailed the prioritized criteria for the ESG indicators providing a holistic theoretical understanding of PPPs activities that present an understanding of ESG outlook. In addition, the RII values and criterion weight present the relevance of each criterion by ESG researchers. This theoretical contribution provides insights into the association between PPP projects' sustainability and ESG assessment criteria. This investigation and conceptualisation present the possible interdependencies that exist between PPP ESG indicators and provides a sound theoretical basis for ESG PPP assessment criteria.

ESG consideration is to foster a sustainable investment decision making, the SDGs, equator principles and ESG assessment are to ensure that PPP projects and large-scale development projects appropriately consider potential impact on the environment, society, and communities. The findings of this study serve as checklist for investors to identify PPP projects key practices of ESG, thereby enabling them to assess the potential of a project in their decision making. The study's findings highlight the importance of evaluating and addressing environmental impact, social responsibility, and governance practices in infrastructure development. This study does not only encourage the integration of ESG into PPP investment projects but also underscores how these interrelated and intra-related criteria positively determine project sustainability. By assigning weights and ranks to each criterion identified, the study sheds light on the delicate balance that needs to be achieved for project sustainability. The study's findings also have implications for public sector entities and private sector investors involved in PPP projects. By understanding the importance of ESG criteria, both parties can make informed decisions, mitigate risks, and maximise the long-term value of their investments. Additionally, the study contributes to the development of industry-focused baseline assessment checklist for evaluating ESG within PPP investment projects, improving the quality and reliability of ESG assessments. Ultimately, these assessment criteria facilitate effective ESG assessment of PPP projects for an enhanced sustainable investment project.

Despite the significant contribution this study presents, the study is limited by the following: the list of criteria presented are implicitly determined and were not explicitly assessed for significant factors through exploratory factor analysis. Further study needs to provide an assessment of the identified criteria and explore their contribution to PPP ESG assessment. Further research should investigate which of the ESG indicators improve a project sustainability performance and how strong the influence is determining investment decisions. Also, identifying some moderator variables that explain this situation considering the PPP projects peculiarities will be essential in future research.

This paper constitutes a part of a PhD research project being conducted at the School of Engineering, Design and Built Environment at Western Sydney University, Australia. This research was supported by the Commonwealth through an Australian Government Research Training Program Scholarship [DOI: Link to the DOI].