A Systematic Review of Sustainability Criteria in Infrastructure Development

Abstract

This paper explores the immediate need of infrastructure stakeholders for practical guidance promoting sustainable infrastructure development that aligns with the United Nations Sustainable Development Goals (SDGs) and European Union (EU) regulations. Despite overarching definitions, there is a noticeable absence of a uniform set of sustainability criteria, which delays the integration of sustainability principles into infrastructure planning, development, and operations. Through a targeted content analysis of the systematically selected literature from the Web of Science, this study seeks to clarify the characteristics of sustainable infrastructure. In the systematic review of 106 sources, carefully selected through a structured exclusion process described in the Open Science Framework register, the authors construct a comprehensive set of 43 sustainable infrastructure characteristics. Subsequently, these indicators undergo evaluation by sector experts through focus group discussions on the relevance of the proposed sustainable infrastructure criteria to local planning contexts. The focus group’s results demonstrate the adequacy of the proposed criteria, albeit with variations in perceived importance. Additionally, participants in the focus group suggest conducting field tests of the criteria in a municipal setting before scaling up to national policy frameworks.

1. Introduction

The United Nations Sustainable Development Goals (SDGs) outline the need for sustainable, climate-neutral, and resilient infrastructure. This aligns with specific efforts and regulations within the European Union (EU). For instance, the EU Taxonomy Regulation sets criteria for environmentally sustainable investments, including technical standards for certain infrastructure elements.

Sustainable infrastructure has been defined by various global and EU organizations like the United Nations, the Organisation for Economic Co-operation and Development (OECD), the European Investment Bank, and the European Bank for Reconstruction and Development. It refers to transport, energy, water, or other infrastructure that is planned, constructed, managed, and decommissioned in a manner that promotes economic, environmental, and social sustainability throughout its lifecycle. It encourages sustainable decisions and actions by stakeholders, supports global commitments like the Paris Agreement and the SDGs, and withstands climate change and other disruptions. These definitions often refer to and are based on the report of the World Commission on Environment and Development: Our Common Future (also known as the Bruntland Report) [1], which defines sustainable development as development which meets the needs of the present without compromising the ability of future generations to meet their own needs. Hendricks et al. [2] define sustainable infrastructure as “systems that have the capacity to endure over a long period of time; enabling the human-built environment to thrive and providing an opportunity for human society to improve its quality of life, without compromising the integrity and availability of natural, economic, and social assets for future generations”.

In practice, these definitions lack specificity and fail to offer practical guidance to infrastructure owners, managers, and planners, both in the public and private sectors. They do not outline the specific considerations necessary for developing sustainable infrastructure, nor do they suggest actionable steps for the public sector to support its development. This has also been recognized by Endo et al. [3] who analysed financing of sustainable infrastructure but identified an issue that there was no uniform definition and specific criteria for sustainable infrastructure itself.

The global demand for sustainable infrastructure solutions is rapidly escalating, driven by the need to mitigate climate change and ensure long-term resource availability. This urgency is underscored by the flourishing of research on the topic. A recent Scopus search using the term “sustainable infrastructure” yielded over 1200 papers, with engineering taking the lead. Endo et al. [3] emphasize that there are two broad categories of research on sustainable infrastructure—technical (design and construction approaches) and non-technical (project planning and decision-making approaches). Han & Kim [4] advocate for a broader perspective that goes beyond just technological advancements in transportation systems, highlighting the need for a more holistic approach. Hendricks et al. [2] conclude that research on sustainable infrastructure combines the perspectives of civil engineering and social planning, with the social dimension increasing in significance. At the same time, the social aspect requires increased stakeholder engagement, but too little attention has been devoted to stakeholder training to enable their meaningful participation in infrastructure planning. One of the most significant challenges is fragmentation. Research delves into at least eight distinct infrastructure sectors, including construction [5,6], transportation systems [7,8], energy [9,10], and waste management [11]. While this breadth demonstrates the multifaceted nature of infrastructure, it also presents significant challenges. Evaluating the success of a sustainable transportation system, for instance, becomes difficult without considering its interaction with energy infrastructure and urban planning [12]. This fragmented approach makes it challenging to develop uniform policies or standardized evaluation methods that can be applied across different sectors. The need for a holistic approach that considers the interconnectedness of various systems is underscored in research on critical infrastructure [13] and knowledge infrastructure [14]. Moreover, Hendricks et al. [2] highlight that the focus is often being placed on sustainable infrastructure development, with an emphasis on new projects and structures, but maintenance and operations of the already existing infrastructure are equally significant. This is acknowledged by Munyasaya & Chileshe [15], stating the increasing understanding among infrastructure professionals that sustainable solutions should be incorporated in the design, construction, and operation of infrastructure facilities. This indicates the need for an evolution of the sustainable infrastructure concept. Additional evolution trends have been identified by Ferrer et al. [16], highlighting that the topics and themes related to sustainable infrastructure have already evolved from the revitalization of slum areas and degraded spaces to more sophisticated topics such as disaster mitigation, the management of urban vulnerabilities, and smart cities.

Compounding this issue is a lack of consensus on how to measure success. Studies grapple with developing appropriate assessment indicators [7,8]—for instance, a focus on environmental impacts may differ from economic considerations. However, because of the absence of a common framework, the true impact of state interventions remains unclear [17] and makes it difficult to determine if current strategies are truly promoting sustainable infrastructure development across different sectors. This challenge is further amplified by the fragmentation within the research field (as discussed earlier). Furthermore, Chatzimentor et al. [18] point out the lack of a universally accepted definition of “sustainable infrastructure,” leading to diverse research objectives and outcomes. This results in difficulties in comparing and building upon existing research, hindering advancements in the field.

The fragmented research landscape, coupled with the lack of consensus on how to assess and evaluate sustainable infrastructure, creates a critical blind spot. This highlights the need for further research that bridges these gaps. This study delves into the existing understanding of sustainable infrastructure, specifically by addressing the research question: “What are the characteristics of sustainable infrastructure?” Building on research conducted by Endo et al. [3] and other researchers who have already analysed the driving factors for sustainable infrastructure, the authors of this study aimed to identify a specific set of criteria which can further be combined and quantified to build a structured decision-making model. By defining these characteristics within a holistic framework, this study can pave the way for the development of more unified assessment methods and effective strategies for sustainable infrastructure development. This understanding can ultimately guide the development of more effective and measurable strategies for sustainable infrastructure development across different sectors.

Due to practical constraints, the systematic literature review was limited to the following:

• OECD and EEA countries.
• Development; Public administration; Regional planning and Urban Studies. These areas offer a comprehensive view of infrastructure development without delving into complex fields like engineering or environmental science but capturing the perspectives of decision-makers (public authorities) and considering their approach to regional and urban infrastructure planning.
• Triangulation was achieved through a focus group comprised of a diverse range of decision-makers representing municipalities of Latvia, a Northern European country, as the literature review highlighted a shortage of research on sustainable infrastructure in this region, which may have different priorities than many of the Asian, American, and other countries which have been studied more often—Northern Europe has colder winters, a more humid climate, and other specific challenges which may affect development of sustainable infrastructure in different ways.
• While this research provides an understanding of the criteria for assessing sustainable infrastructure, developing an indicator system based on these criteria fell outside the scope of the current study.

The remaining part of the paper proceeds as follows: Section 2 provides a comprehensive overview of the methodology used for this study. Section 3 analyses the results of the literature review and triangulation of the results within the focus group. Section 4 presents the findings of the research, focusing on the research question formulated above.

Throughout this paper, the term “sustainable infrastructure” corresponds to the definition outlined in the second paragraph of this section. When discussing the systematic literature search, content analysis, and focus group, we are referencing the methodology detailed in Section 2.

This systematic review has been registered with the Open Science Framework (OSF) and is available online: https://osf.io/ztb9n/ (accessed on 22 May 2024).

2. Materials and Methods

We adopted a three-stage research design encompassing a systematic literature search, content analysis of the selected content, and a focus group for triangulation of the obtained results (see Figure 1). Each step is thoroughly described below, outlining the methodologies employed and procedures followed. All materials utilized and manipulations performed throughout the study are comprehensively detailed in annexes, facilitating the replication and further development of the published results. No restrictions on the availability of materials or information were imposed, ensuring transparency and accessibility for future research endeavours.

To mitigate bias in our review process, we implemented specific measures. Firstly, both reviewers underwent comprehensive training in systematic literature review methodologies, inductive content analysis techniques, and bias risk assessment. This training aimed to ensure consistency and accuracy in evaluating the included studies. Secondly, to further strengthen our approach, we conducted a focus group, the details of which are described below. Reviewers independently assessed each study for inclusion and risk of bias.

In our study, we employed Cohen’s Kappa scale to evaluate the level of agreement between independent reviewers during the bias assessment process. After independently evaluating each study for inclusion and risk of bias, we found substantial agreement between the reviewers, as indicated by a Cohen’s Kappa coefficient of 0.7. This suggests a high degree of consistency in our evaluations and the reliability of our findings.

Further sub-sections detail each step of the study, explaining the methodologies and procedures employed in the systematic literature search, content analysis of selected content, and the focus group.

2.1. Systematic Search Strategy

A multifaceted search strategy was employed, utilizing keyword combinations, filters, and targeted inclusion criteria (as detailed in Figure 2, according to PRISMA 2020 flow diagram (see Supplementary Materials) [19]).

Web of Science (WoS) database was selected for conducting a systematic review.

The selection of the search terms was grounded in the desire to explore the concept, components, and implementation frameworks of sustainable infrastructure from a multidimensional perspective:

• “Criteria of sustainable infrastructure” indicates our interest in understanding the specific criteria or metrics used to evaluate infrastructure projects’ sustainability. With this search, we explore the methodologies and frameworks used to assess sustainability in infrastructure development.
• “Sustainable infrastructure components” suggests an inquiry into the various elements or components that constitute sustainable infrastructure projects. This search focused on components such as renewable energy systems, green building materials, efficient transportation networks, and water management solutions.
• “Sustainable Development Goals and infrastructure planning” reflects infrastructure planning and aims to examine strategies for aligning infrastructure planning with the indicators set forth by the United Nations.

The selection of search terms demonstrates an all-inclusive approach to understanding sustainable infrastructure evaluation criteria and their relationship with broader sustainable development objectives. We combined these terms using AND operators.

A considerable amount of the literature has been published on the research topic. Therefore, to maintain the focus on high-quality studies in the field of social studies, eligibility criteria were introduced based on the goal and objective of the study. Details about the rationale for each inclusion and exclusion criterion are provided in

Table 1. Inclusion and exclusion criteria.

Step	Characteristics	Inclusion Criteria	Exclusion Rationale
Filter 1	Categories	Development studies, Public administration, Regional urban planning, Urban Studies	To exclude fields outside of the authors’ scientific area (e.g., engineering, medicine, law).
	Document types	Articles, Books, Book chapters	To collect data from primary sources
	Languages	English	To understand the content of the study
Filter 2	Countries covered	OECD and EEA countries only	Focus on similar systems
	Scope of analysis	Narrow case studies	To understand a broader phenomenon or develop more generalizable insights

.

By specifying these exclusion criteria and their rationales, a systematic framework for selecting studies that align with research objectives in the field of social studies was developed to promote transparency and rigor in the review process. To ensure consistency in our paper-selection process, we employed a two-reviewer approach for classifying the retrieved papers. Each reviewer independently categorized the papers based on the pre-defined inclusion and exclusion criteria. The initial classifications of both reviewers were in alignment.

The initial filtration process was conducted utilizing built-in filters integrated within the WoS platform. The second filtration was conducted manually in three phases by two independent reviewers. Each reviewer operated autonomously, with any disparities or uncertainties being deliberated upon and resolved through consensus:

• The initial screening aimed to exclude overlapping studies assessing the titles and abstracts for relevance. Studies that passed this phase proceeded to the next level of screening.
• During the second phase, duplicates were excluded, and the remaining studies were subjected to a more detailed assessment of exclusion criteria, where two reviewers independently evaluated the full texts, excluding papers that primarily dealt with case studies or analysed regions that are not part of the OECD or EEA countries.
• In the final phase, studies were excluded in areas outside the scope of the object (e.g., sustainability in agriculture, school development, or residential buildings).

Automation tools were not used in the screening process; instead, manual screening was employed to maintain an elevated level of scrutiny and ensure accurate identification of eligible studies. Manual screening allowed reviewers to consider contextual nuances and make informed decisions based on the inclusion criteria.

As a result of the limitations and additional review of the sources, the authors came up with 106 sources for further content analysis.

2.2. The Content Analysis of the Selected Studies

In this study, we employed Mayring’s [20] qualitative content analysis procedure as our guiding framework. The selected data underwent a systematic analysis, wherein content analytical units were identified incrementally, aligning with the research question, and subsequently organized into categories. We structured our criteria around the well-known Environmental, Social, and Governance (ESG) categories. To comprehensively assess sustainable infrastructure, we included an additional category focusing on state intervention economic benefits. These categories were established and refined throughout the analysis process through iterative feedback loops. Our approach involved inductive category development, as illustrated in Figure 3 and elaborated upon in subsequent text.

The procedure focused on indication of categories derived from the research question, which served as the framework for analysing textual material. Initially, a draft definition for each category was established and subsequently refined based on subsequent pieces of information. As the analysis progressed, the material was systematically reviewed, and all categories underwent continuous revision within a feedback loop. The purpose of this iterative process was to continuously update the categories and those definitions, eventually consolidating them while ensuring their reliability. Additionally, quantitative aspects, such as the frequencies of coded categories, were examined. Therefore, the final number of sources reviewed for this study stands at 106.

The sustainable infrastructure criteria identified within content analysis were further tested with a focus group composed of representatives of city development and territorial planning experts from five city municipalities of Latvia.

2.3. Triangulation within Focus Group

The benefits of the focus group method include collecting immediate, in-depth reflections on the material under discussion from a diverse group of stakeholders. To engage the municipalities, the research team contacted the Latvian Association of Local and Regional Governments and selected participants to ensure diversity, representing both larger cities and smaller municipalities (and excluding the capital city) in Latvia and providing wide geographical coverage of the country, as shown in Figure 4.

A total of seven participants were recruited for the focus group. Participants included three males and four females. However, we employed a purposive sampling strategy, targeting individuals with relevant expertise and experience in infrastructure planning.

The focus group session lasted for approximately two hours. The participants of the focus group were introduced to the findings of the targeted content of the selected literature via an MS Teams meeting. Subsequently, they were guided question by question to provide their feedback using predefined questions on the Padlet platform (see the screenshot in Figure 5; the depiction of the questionnaire is provided in Table S2).

The prearranged questions were structured to obtain the participants’ views on the relevance of the presented list of sustainable infrastructure criteria to infrastructure planning in their cities or counties, prioritization of the criteria in the short- and medium-to-long-term timespans, and the stakeholders’ experience with obstacles and drawbacks to sustainable infrastructure planning. Additionally, participants were encouraged to comment on and vote for other participants’ proposals. We provided participants with the option to choose between anonymous and identified records, although it was likely that all municipalities were open to sharing their feedback in identified ways. We also provided participants with the opportunity to amend their records within 24 h following the conclusion of the entire focus group. This allowed participants to review their contributions and make any adjustments or additions they deemed necessary based on further reflection or insights gained during the discussion. When summarizing the results of the focus group, we repeated the qualitative content analysis loop to ensure thoroughness and accuracy in our findings.

The following section of this paper moves on to describe, in greater detail, the results achieved in the study.

3. Results

This section presents the results of the study based on the methodology described above.

3.1. Results of Systematic Literature Search

In the systematic literature search, we examined papers from diverse fields such as urbanism, engineering, economics, sociology, and geography. These fields often operate independently with limited cross-referencing [21]. Therefore, before categorizing sustainable infrastructure criteria, we provide a brief overview of the disciplines represented in the selected papers. Figure 6 illustrates the distribution of the focus of the included articles.

A total of 37 out of 106 of the articles discussed green infrastructure with an emphasis on greenery and natural vegetation in urban spaces, including streets, parks, walkways, urban forests, and walls and roofs of various buildings and structures ([22,23,24], etc.), as well as other aspects of nature-based solutions, biodiversity preservation, or facilitation in the urban environment [12,25,26].

Another 32 articles dealt with various types of water management systems, including water supply, wastewater treatment, stormwater management, and drainage ([8,27], etc.). It should be noted that in many cases, water management infrastructure was viewed by authors not only through the lens of sanitation, sufficient water supply, and other direct functions of a water system but also from the perspective of being a potential means of dealing with risks created by climate change—such as storms and floods causing excessive amounts of water endangering cities [8,28]. In addition, several authors referred to nature-based solutions—such as lawns, ponds, or wetlands—that may be used to successfully address stormwater management and drainage issues in an urban environment [29,30]. Most often, the water management systems were viewed along with green spaces, considering that nature-based solutions may prevent flooding and, thus, the risk to a specific territory [31] or that efficient water management systems may facilitate biodiversity in an urban environment [32].

Besides green spaces and water management, the researchers also discussed transport and energy infrastructures (24 out of 106 observed publications). With regards to energy infrastructure, authors emphasised the transition to zero-carbon or decarbonised solutions [33], which also include the use of smart technologies to reduce energy consumption [34], as well as just transition that considers the needs of socially vulnerable societal groups [35]. For transport, some of the most distinct topics for discussion included the planning and facilitation of more sustainable transport infrastructure [30,36], data-driven solutions that may help in the planning process [26], and the introduction of new transport solutions and related infrastructures—such as hydrogen transport [37] or self-driving cars [38]. At the same time, researchers noted that transport infrastructure has a broader role in facilitating sustainability not only from the environmental perspective but through the enhancement of mobility and connectivity which provide social benefits, such as access to work, education, healthcare, and other significant public services [39,40].

A few of the authors also discussed housing and waste management [41] as components of sustainable infrastructure. Specifically, waste management was analysed in line with the availability of infrastructure and the means for citizens to sort, reuse, and recycle waste, thus contributing to the circular economy where practically possible.

Circularity, biodiversity, landscape, and other aspects are often also seen through the lens of the above-mentioned categories. For instance, Suleiman et al. [42] discuss the collection of rainwater and other residual water that may be treated for further use in irrigating urban vegetation and reducing expenditure for water consumption.

In this systematic literature review, a wide range of sustainable infrastructure topics were explored across the analysed articles. Three primary areas emerged: the role of greenery and natural vegetation in urban environments; water management systems, particularly in addressing climate change-related risks like storms and floods; and transport and energy infrastructures, with a focus on transitioning to zero-carbon solutions and integrating smart technologies. Waste management, circularity, biodiversity, and landscape considerations received less attention. This highlights the importance of recognizing the multifaceted nature of sustainable infrastructure when interpreting the results of content analysis.

3.2. Results of the Content Analysis

This subsection describes the results of the content analysis performed and described in Section 2.2.

The initial categorization process began by considering three fundamental aspects of sustainability: Environmental, Social, and Governance, often alongside economic factors ([41,42,43], etc.). Results from this initial iteration revealed that these categories were mentioned 216, 190, 0, and 138 times, respectively, indicating a slightly higher emphasis on environmental aspects (39.71%) compared to social aspects (34.93%), with no exclusive focus on governance identified. Notably, around 25.37% of the references discussed the economic impact, albeit often treated as a conventional rather than sustainability-related topic. Following this, 43 specific criteria were identified outside of the broader categories of environment, social, and economic aspects, each defined in detail (refer to Table S1, “Definitions” sheet). For each of the developed criteria, mentions varied from as low as 3 times (e.g., potential for experiments) to as high as 119 times (e.g., mitigation of pollution) throughout the analysed quotes. The authors categorized each criterion into broader categories, as depicted in Figure 7a. Notably, the environment emerged as the dominant category in assessing the sustainability of infrastructure, with 715 mentions, representing approximately 33% of the total mentions. Following closely behind were governance and social responsibility, each comprising 24% of the mentions, with 530 and 527 mentions, respectively. Conversely, economic aspects appeared less prominently, with 396 mentions, constituting approximately 18% of the total mentions.

For the sake of further analysis, the authors spotlighted the Top 20 mentions, which served as the foundation for addressing the initially defined research question on the characteristics of sustainable infrastructure (see Figure 7c). Categories that did not rank within the Top 20 in terms of frequency of mentions or implications in the analysed articles include the promotion of circularity, care for biodiversity, enabling ecosystem services for citizens, social inclusiveness and justice, creation of open spaces for citizens, facilitation of responsible consumption, creation of attractive landscapes, resource efficiency encompassing long-term infrastructure maintenance, revitalization of neglected areas or other territories, functionality and multi-functionality, adaptivity, orientation for a long-term perspective or future-proof approach (which may overlap with the strategic approach included among the Top 20 criteria), and specific aspects of risk-based planning and regional cooperation, among others.

The criteria included among the Top 20 cover all four broader categories. Compared to the total selection mentions, the reduced selection also highlights the dominance of the environment as the primary category in assessing the sustainability of infrastructure, accounting for approximately 35% of the total mentions. The proportion of governance-related criteria increased to 32%. Conversely, criteria related to social and economic aspects appear less prominently, with 21% and 12%, respectively.

The content analysis revealed a notable but counterintuitive trend: criteria aimed at mitigation processes were mentioned more often than criteria highlighting preventive strategies. Several factors could explain this emphasis on mitigation. The literature reviewed may have predominantly focused on improving the sustainability of already built infrastructure, where mitigation becomes the primary option for addressing existing environmental issues. Secondly, the research reviewed may have emphasized mitigation due to the perceived difficulty or complexity of implementing effective preventive measures during the planning and design stages because integrating sustainability considerations during the initial stages of a project requires a more comprehensive approach. Another possibility is that there is a gap in current research on preventive strategies for sustainable infrastructure development. This lack of readily available knowledge could lead to a bias towards mitigation within the analysed literature.

Figure 8 illustrates the set of Top 20 criteria, which was presented to the focus group for evaluation as a potential set that can be used for the assessment of infrastructure project sustainability.

The set of criteria presented to the focus group for triangulation under the economic aspects category included three criteria:

• “Contribution to mobility and connectivity” evaluates how infrastructure development or operations contribute to improving mobility and connectivity between different areas, as well as enhancing informative connectivity. It assesses the extent to which the infrastructure facilitates movement and communication, thereby promoting accessibility and integration.
• “Resilience” examines whether the infrastructure is designed or managed to withstand external or internal stressors, such as severe weather conditions or attacks. It assesses the infrastructure’s ability to continue operating or quickly resume operations after encountering disruptions, thereby ensuring its reliability and continuity.
• “Use of innovations” evaluates whether infrastructure development or operations incorporate novel solutions, technologies, innovative materials, or approaches. It assesses the extent to which the infrastructure embraces innovation to improve efficiency, effectiveness, and sustainability.

The set of criteria presented to the focus group for triangulation under the social responsibility category includes six criteria:

4.

“Accessibility” evaluates whether the infrastructure and its use are physically accessible to diverse groups of users and financially accessible or affordable. It assesses the inclusivity of the infrastructure, ensuring that it can be accessed by all members of the community, regardless of their physical abilities or financial means.

5.

“Ability to empower communities” examines whether infrastructure development or operations enable the local community to discover and utilize new opportunities for their benefit. It assesses the extent to which the infrastructure fosters community empowerment, such as facilitating the development of local family businesses or youth initiatives.

6.

“Contribution to quality of life” evaluates whether infrastructure development or operations improve the well-being of citizens in the respective area and their satisfaction with living, working, or studying there. It assesses the impact of the infrastructure on enhancing the overall quality of life for the community.

7.

“Focus on public health” assesses whether the use of infrastructure creates additional benefits for public health, such as improving air quality, facilitating biking or walking, or creating public open-air gym spaces. It examines the infrastructure’s contribution to promoting public health and well-being.

8.

“Incorporation of educational element” evaluates whether infrastructure development or operations are complemented with educational activities, such as educating citizens on the use of the new infrastructure or its benefits or using the infrastructure for education on specific environmental or social aspects. It assesses the infrastructure’s role in promoting learning and awareness within the community.

9.

“Safety and security” assess whether the use of infrastructure poses safety or security threats. It examines whether the infrastructure design and operations mitigate physical hazards, accidents, or security threats that may endanger people’s safety, health, and life, ensuring the well-being and security of the community.

The set of criteria presented to the focus group for triangulation under the governance category includes six criteria:

10.

“Use of smart technologies” evaluates the use of ICT-managed intelligent systems in infrastructure projects, promoting sustainability through resource optimization, efficiency improvements (e.g., lower energy consumption), and preventive maintenance (extending infrastructure lifespan). This criterion assesses the utilization of complex data analysis models, artificial intelligence solutions, blockchain technologies, smart meters, and other approaches to enhance the infrastructure’s overall sustainability.

11.

“Strategic approach” assesses the adoption of an integrated approach for infrastructure planning, wherein potential projects and actions are thoroughly analysed, prioritized, and assessed from a medium- to long-term perspective. It considers factors such as funding availability and systematic implementation decisions resulting from the analysis.

12.

“Stakeholder engagement” evaluates the implementation of a structured and targeted process for communication and consultation with stakeholders who may have opinions, concerns, or suggestions regarding specific infrastructure projects or infrastructure development in a certain area. It emphasizes the importance of involving stakeholders in decision-making processes.

13.

“Data-based design and operations” assesses whether infrastructure design and operations are based on empirical, systematically collected data. It focuses on data-based decision-making processes to ensure informed and effective infrastructure planning and management.

14.

“Changes in governance practices” examines the institutional system and its transformation towards practices that support sustainable infrastructure development. This includes adopting lifecycle costing approaches, fostering stakeholder participation in decision-making processes, and promoting transparency.

The set of criteria presented to the focus group for the triangulation under the environment dimension includes five criteria:

15.

“Mitigation of pollution” assesses whether infrastructure is built or managed to decrease the contamination of soil, air, or water. It considers strategies such as the revitalization of contaminated areas or designing infrastructure to create less pollution than that traditionally produced by specific infrastructure or its operations.

16.

“Ability to mitigate external impact” evaluates whether infrastructure is specifically built to mitigate external environmental impacts that are outside people’s control, such as extreme weather conditions like storms or floods and their consequences. It assesses the infrastructure’s resilience and ability to withstand and mitigate such external impacts.

17.

“Existence of green spaces” examines the presence of natural or deliberately created vegetation in urban environments. It considers how green spaces improve air quality, contribute to people’s well-being and health, and enhance the aesthetics of an area.

18.

“Ability to address climate change” assesses whether infrastructure is built or managed to either mitigate climate change by creating fewer greenhouse gas emissions than traditionally generated by specific infrastructure or its operations or adapt to climate change by operating successfully under changing climate conditions such as increasing temperatures and rapidly changing weather.

19.

“Nature-based solutions” evaluate whether natural capital or the natural environment is respected and used in a positive way to build and operate specific infrastructure. It considers the utilization of nature-based solutions, such as using existing ponds, wetlands, and other natural formations for stormwater management purposes.

20.

“Integration with other infrastructures” evaluates whether infrastructure is integrated with other types of infrastructures or if sustainable elements are integrated into conventional infrastructure to enhance its sustainability. It assesses the interconnectedness and synergy between different infrastructure systems to maximize their effectiveness and sustainability.

To ensure a comprehensive framework for evaluating the sustainability of infrastructure projects, we presented a shortlist of 20 criteria to the focus group, encompassing economic, social, governance, and environmental dimensions. To minimize bias and account for potentially relevant topics beyond the initial list, we also provided an extended list of 43 criteria with definitions for participant consideration and prioritization. Cross-referencing the Top 20 as well as the extended list of criteria with the findings of Endo et al. [3] in their recent research performed around the same time as our research, there are many overlapping criteria—for example, climate change mitigation, resource efficiency, circular approaches, community orientation, and stakeholder participation and collaboration.

The focus group discussions emphasized the importance of diverse criteria for a holistic assessment of multifaceted sustainable infrastructure. Furthermore, we encouraged participants to imagine making future infrastructure project decisions, fostering a long-term perspective.

The next section explores insights from the focus group discussions on the criteria for sustainable infrastructure.

3.3. Results of the Focus Group

The sustainable infrastructure criteria identified in the initial phase of the research underwent further examination through a focus group consisting of representatives from city development and territorial planning experts from five municipalities in Latvia. The utilization of a focus group method allowed for the collection of immediate and in-depth reflections from a diverse array of stakeholders. To ensure engagement from municipalities, the research team collaborated with the Latvian Association of Local and Regional Governments and selected participants representing both larger cities and smaller towns across Latvia, ensuring broad geographical coverage and diversity in perspectives.

The participants of the focus group were initially briefed on the findings of the literature review and subsequently invited to provide their feedback using a questionnaire hosted on the Padlet platform. The questionnaire aimed to gather participants’ perspectives on several key aspects, including the following:

• The relevance of the presented Top 20 list of sustainable infrastructure criteria to infrastructure planning in their respective cities;
• Criteria identified for potential inclusion in the Top list from the comprehensive list,
• the prioritization of these criteria in both short-term and medium-to-long-term contexts;
• Insights into stakeholders’ experiences regarding obstacles and drawbacks to sustainable infrastructure planning.

Overall, the sustainable infrastructure criteria presented by the research team were acknowledged as sufficient for real-life infrastructure planning by the participants. Some participants noted that they already utilize similar criteria in their professional practice. These recognized criteria from the Top 20 are highlighted in bold in Figure 9. Participants acknowledged that some important criteria, though not included in the initial Top 20 list, were identified within the comprehensive list. Those are included in the column “Additional criteria mentions” in Figure 9.

The focus group discussions on social responsibility for sustainable infrastructure yielded interesting findings. While participants generally agreed and highly scored the Top 20 criteria presented (yellow part of Figure 9), except for the “Incorporation of educational element” that did not resonate with the group, participants emphasized the importance of additional social responsibility criteria. These mostly included aspects such as inclusivity, community empowerment, and respect for local context. This information will contribute to refining the framework for the evaluation of local sustainable infrastructure projects.

The focus group discussions delved into the importance of good governance practices for sustainable infrastructure development. Two criteria from the Top 20 list, “Data-based design and operations” and “Changes in governance practices,” did not resonate much. This suggests that participants may have felt these areas were already adequately addressed or perhaps needed further definition. The discussions highlighted several other governance criteria beyond the Top 20 considered highly important. This included a strong endorsement of adopting a circular approach in infrastructure development, the importance of considering future reconstruction needs during the initial design and planning phases, and a strong focus on proactive risk management throughout the infrastructure development process. These criteria highlight the focus group’s emphasis on long-term planning and responsible stewardship of infrastructure projects.

The focus group strongly agreed that sustainable infrastructure should help improve mobility and connectivity; however, some participants considered “mobility and connectivity” more as social rather than purely economic indicators. They believed that these aspects are crucial for enhancing people’s quality of life and fostering community cohesion rather than solely contributing to economic growth. When discussing economic aspects, participants focused on a broader range of factors than presented in the Top 20 list. They consistently emphasized the importance of long-term value, responsible resource use, and efficient operation. The discussions highlighted the need for infrastructure to serve multiple purposes effectively, maximizing its economic benefits and promoting responsible consumption. Participants stressed the economic advantages of ensuring that infrastructure can seamlessly connect and work with existing systems, reducing the need for redundant investments, and making better use of resources. These findings suggest that, when it comes to sustainable infrastructure development, the group valued practical considerations and consideration of costs over the entire lifespan of the infrastructure.

The focus group discussions on environmental criteria for sustainable infrastructure development yielded some intriguing results. The top-ranked criteria, which included “Mitigation of pollution” and “Ability to address climate change”, received somewhat lower scores compared to other environmental aspects. The focus group participants, especially those from municipalities outside the capital city, might perceive their current environment as relatively satisfactory. This could lead to a sense that the immediate mitigation of pollution or climate change actions are fewer pressing concerns than other infrastructure needs. Contrarily, the discussions emphasized more localized environmental concerns, such as biodiversity preservation, the revitalization of specific areas, and the creation of attractive landscapes. Therefore, it is also important to consider that the priority given to different criteria could vary depending on the specific context of an infrastructure project. For instance, a project in a highly polluted area may necessitate a stronger focus on mitigation strategies, while another project in a neglected area might prioritize revitalization efforts.

Overall, the participants recognized the sufficiency of most Top 20 sustainability criteria presented by the research team for real-life infrastructure planning. Moreover, some participants indicated that they were already implementing similar criteria in their professional practice. Additionally, participants highlighted the importance of project continuity, reaching a significant number of beneficiaries, and meeting multiple objectives with a single project. Moreover, the readiness of the project and the availability of external financing such as EU funds, political support, and contributions to balanced territorial development were identified as key considerations.

As evident from the Top 20 criteria prioritization by the focus group (see Figure 9), the majority emphasized the social benefits that infrastructure can provide. This contrasts with findings from the literature review, where authors emphasized the pivotal role of environmental criteria when defining sustainable infrastructure, with social benefits being mentioned less frequently. However, when asked to consider potential projects 10–15 years from now, the participants emphasized that they see more utility in the following criteria: integration with other types of infrastructure, nature-based solutions, mitigation of pollution, mitigation of external impact, as well as safety and security, which will gain even more importance.

The focus group also elaborated on the challenges they encounter in the development of sustainable infrastructure. According to their experience, these challenges include the following:

• Data collection, processing, and analysis are often conducted insufficiently due to a lack of resources.
• Insufficient awareness and/or understanding from decision-makers on sustainability and its relevance to infrastructure development and decision-making.
• Lack of political support.
• Lack of financing for sustainable projects.
• Diverse public opinions and complexity in aligning them, as emphasized by several participants.

For solutions, the participants emphasized the need for clearer communication within the municipality, including its administration, and with citizens. They also stressed the importance of establishing a clear institutional format for project assessment at the executive level rather than the political level, along with a methodology for such assessments. Additionally, they suggested engaging in wider, more detailed discussions with key stakeholders during the project’s inception and planning phases to support further development.

In conclusion, the focus group participants recommended encouraging municipalities to conduct the testing of sustainable urban solutions, sometimes on a smaller scale, to assess their efficiency and usability before scaling up. They also called for greater clarity in national-level policy planning documents, which should highlight priorities in certain sectors more specifically and provide more flexibility for decision-making at the local level, including clear communication on activities that are not supported.

4. Discussion and Dissemination of the Findings

The targeted content analysis of the selected literature reveals that while numerous researchers have examined infrastructure development and urban planning within the context of sustainability, only a limited number have put forth models, tools, or frameworks specifically designed for decision-making purposes.

By acknowledging this limitation and highlighting the need for further research, this discussion section prompts critical reflection on current trends in sustainable infrastructure research. Future studies can delve deeper into understanding the reasons behind the emphasis on mitigation and explore the potential for strengthening preventive approaches within the field.

The analysis of criteria that define sustainable infrastructure underscores some critical aspects, as discussed below.

Firstly, it emphasizes that the assessment of sustainable infrastructure should extend beyond examining individual infrastructure components and should also include spatial planning. Current frameworks for sustainable infrastructure planning [44] address a specific type of infrastructure or are targeted at certain decision-making aspects (e.g., siting decisions). Spatial planning considers the interconnectedness of various infrastructures within a region, recognizing that regional development heavily relies on the cohesion and effectiveness of public infrastructure, as is shown in Heeres et al.’s [45] exploration of a shift in Dutch motorway planning, moving away from a traditional focus on the road itself (line-oriented) to a more comprehensive approach (area-oriented). Also, Meerow [46] emphasizes the importance of long-term, holistic planning, especially for cities. Successful planning requires the support of local government and active participation from engaged stakeholders. This includes professionals, businesses, social organizations, politicians, and the public. Meerow’s [46] approach considers six key benefits (stormwater management, social vulnerability, green space, air quality, urban heat reduction, and landscape connectivity) and allows stakeholders to prioritize them for optimal placement of sustainable infrastructure projects.

Another aspect is providing region-specific perspectives into the common criteria system. These region-specific perspectives stem from historical contexts, societal behaviours, and the concerns of local inhabitants. The findings from focus group discussions support this evidence. For example, Suleiman [47] points out that while Sweden has examples of sustainable, integrated water management infrastructure development, the maintenance activities for these systems are often planned in a traditional manner, which may not ensure their long-term sustainability. Similarly, Newell [22] suggests that developers may create environmentally friendly solutions, but if they fail to integrate social values into these initiatives, the resulting areas may not meet the needs of the local community or enhance its overall quality of life. Verdu-Vazquez et al. [48] emphasise that it is significant to separate strategic city planning from the regular political cycles in municipalities or states, which are often less far-sighted and are more focused on short- to medium-term gains. Other researchers note that sustainable infrastructure planning requires a different approach to governance [49], which often includes multiple external stakeholders, not only public officials [50]. This may initially seem to be a longer decision-making process but may lead to more benefits in the long run as multiple perspectives are considered.

It seems that for complex infrastructure systems, achieving a single solution that perfectly satisfies all criteria is often unrealistic. Instead, the goal should be to identify Pareto-optimal solutions. These represent compromises where no single criterion can be improved without making another worse. This set of Pareto-optimal solutions may also include locally efficient solutions that excel in a specific criterion. These can be particularly valuable when addressing the unique needs of different regions. By considering both comprehensive and locally efficient options, the framework can be more adaptable and effective in addressing the diverse challenges of infrastructure development across a wide range of contexts. Moreover, the importance of various criteria is likely to continually evolve in response to climate change, evolving societal needs, economic considerations, and technological advancements.

During discussions with the focus group participants, we found that some conflicts can be resolved by refining definitions. For example, during discussions, we noted that the “resilience” criterion had been excluded from the prioritized criteria due to participants’ unfamiliarity with the exact meaning of the term. We provided a definition from the Oxford Languages dictionary (accessed on 8 June 2023) as “the capacity to withstand or recover quickly from difficulties; toughness” and “the ability of a substance or object to spring back into shape; elasticity”, and determined that participants understand this aspect as meaning “functionality” and “maintainability”. By clarifying definitions, a shared understanding of sustainable infrastructure can be developed, aiding all stakeholders involved in infrastructure planning to effectively utilize their resources for maximum benefit.

Finally, the list of chosen criteria must be supplemented with specific indices and frameworks for comprehensive assessment. Furthermore, it should undergo testing through specific case studies to evaluate its practical utility and applicability to real-world decision-making processes. There is existing evidence of approaches with frameworks and indices, such as the Functionality–Resiliency–Sustainability Framework [44], Composite Index [51], and decision criteria systems for evaluating sustainable infrastructure development [52]. However, these tools may be tailored for specific infrastructure types, focused solely on siting decisions without considering future maintenance, or they may lack a comprehensive approach that incorporates all stakeholders’ perspectives into decision-making. Therefore, one of the future research directions for the authors is to develop a decision-making model for the planning, implementation, and maintenance of sustainable infrastructure in urban areas. Several authors, including Meerow [46], Rodrigues & Franco [51], Suleiman et al. [42], and Ivanova et al. [53], emphasize the significance of assessing value-for-money concepts, which involves measuring ESG characteristics versus the economic benefits of state intervention. For future research, it would be beneficial to execute the same concept.

As a conclusion, we would like to highlight two critical aspects that can be distinguished from this study: firstly, the importance of considering spatial planning alongside individual infrastructure components, and secondly, the necessity of incorporating both common criteria and region-specific perspectives into assessment frameworks, to ensure more effective decision-making in sustainable infrastructure development.

5. Conclusions

This research has delineated a set of characteristics that may define sustainable infrastructure and influence its development. While environmental factors are frequently cited, social and governance aspects emerge as equally significant in shaping infrastructure development processes. Moving forward, the identified characteristics require validation with input from policymakers and industry experts, along with alignment with existing regional development indices and tools. Further refinement through the establishment of clear indicators will enhance the practical utility of a decision-making model for sustainable infrastructure development. The authors intend to advance this model in subsequent phases of their research, incorporating testing and validation processes.