Development of Stakeholder Engagement Strategies to Improve Sustainable Construction Implementation Based on Lean Construction Principles in Indonesia

Abstract

Stakeholder management has an important role in the success of the project because the strategies, plans, methods, and processes for stakeholders greatly determine the success of sustainable construction implementation. Lean construction is one of the principles in implementing sustainable construction by maximizing value and minimizing waste to increase productivity. This study aims to analyze the stakeholder engagement assessment matrix in lean construction, analyze the drivers and barriers in lean construction, and develop stakeholder engagement strategies to improve the implementation of sustainable lean construction. For this study, a questionnaire survey with 61 respondents was used. The data analysis method uses the Certainty Index, RII, Fuzzy AHP, and Fuzzy-TOPSIS. The findings of this research show that there are engagement gaps among stakeholders such as owners, contractors, consultants, subcontractors, architects, the government, local governments, and NGOs. There is no engagement gap between project suppliers and investors. The highest barrier to implementing sustainable lean construction is a lack of knowledge and skills in using lean tools and principles, while the highest driver to implement sustainable lean construction is improved time efficiency and process standardization. The best strategy for increasing stakeholder engagement is by having governments develop regulations and standardize green and sustainable materials.

1. Introduction

Stakeholders are individuals, groups, or organizations that have an interest in influencing or being influenced by the decisions, activities, or outcomes of a project, program, or portfolio [1]. Stakeholders can be defined as parties who have "stakes" or engagement and interests in the project [2]. Project stakeholder management will greatly affect the success of the project. Poor stakeholder management strategies, plans, methods, and processes can lead to project failure.

Indonesia, as one of the developing countries, has a high level of infrastructure development because of the rapid increase in population. However, the construction industry already accounts for 40% of total global energy consumption, 40% of global material consumption, 55% of global timber consumption, and 12.2% of global water consumption [3].

Sustainable construction is one of the solutions to social and environmental problems. Sustainable construction is an approach to conducting construction activities that meet current and future economic, social, and environmental needs. Project stakeholders have an important role in the successful implementation of sustainable construction. The level of stakeholder interest in sustainability principles will determine how sustainable construction is applied to the project.

However, stakeholder interest in implementing sustainable construction still tends to be low. The high initial cost of infrastructure investment required is one of the main financial problems faced by project owners. The lack of clarity on the sustainable components that should be applied to projects is one of the barriers to sustainable construction funding [4]. These factors cause low stakeholder motivation in the implementation of sustainable construction, which leads to poor sustainability planning by stakeholders.

Lean construction is one of the alternatives for implementing sustainable construction on infrastructure projects. Lean construction enables quality improvement and cost reduction to be achieved. By increasing stakeholder engagement in sustainable lean construction, stakeholders can develop a continuous improvement procedure to improve construction efficiency and quality for end-users [5]. However, lean construction has not been well implemented. The previous study shows that UK project stakeholders lack positive attitudes, awareness, and knowledge in using lean tools [6]. The same thing is also found in Indonesia, where the readiness level of contractors in implementing lean construction is still quite low, especially in reducing cycle time and reducing variability [7]. This can result in low efficiency and effectiveness when using lean construction tools. The lack of positive attitudes can also inhibit the implementation of lean construction by other stakeholders. Such barriers as spreading bad rumors about lean tools and even encouraging rejection of the use of lean tools can occur because they are considered too complicated in the construction industry.

A previous study on the strategies for sustainable construction focuses on the use of value management and risk management on sustainability-related performance [8]. Other research discusses how lean construction can improve the implementation of sustainable construction by creating lean performance indicators that are connected to the concept of sustainable construction [6]. Research on awareness, benefits, and challenges encountered by stakeholders also provides a perspective on what barriers and drivers are perceived and accepted by project stakeholders [9]. However, most studies focus on the conceptual framework for developing sustainable construction and lean construction that can be implemented by all stakeholders. Road infrastructure projects, such as toll roads, have diverse stakeholders and different interests. Such integration between stakeholder engagement strategies, lean construction, and sustainable construction is needed to improve sustainable lean construction. It is necessary to analyze the level of influence and level of stakeholder engagement in the decision-making process of sustainable construction implementation to determine the right strategy. It is also necessary to develop a strategy to increase stakeholder involvement in the decision-making of lean construction implementation by analyzing the inhibiting factors of sustainable construction and the benefits offered by lean construction.

Therefore, this study aims to analyze the level of influence and engagement through a stakeholder engagement assessment matrix in sustainable lean construction, analyze the driving factors and barriers to the implementation of sustainable and lean construction, and develop strategies. This strategy can be used to increase stakeholder engagement in the implementation of sustainable construction with a lean construction approach within the sustainable construction criteria contained in The Regulation of the Minister of Public Works and Housing of the Republic of Indonesia Number 9 of 2021 concerning Guidelines for Implementing Sustainable Construction.

2. The Literature Review

2.1. Sustainable Construction

Sustainable construction is achieving a balance of environmental conditions that are not damaged or reduced due to development or activities [10]. The balance and interaction between three aspects, namely, social, economic, and environmental, are needed to be able to achieve the goal of fulfilling current construction needs while also considering the need to meet future needs [11].

Previous studies show that sustainability can be enhanced through improved material quality that increases building life and service life [12]. Improved quality will also increase user satisfaction and safety and achieve sustainability [13]. Sustainability can also be viewed from the financial feasibility of construction, such as the use of LCA [14]. Adding value to construction is also a form of increasing the implementation of sustainable construction. Project value management allows increasing the primary value of infrastructure to add value in the form of reducing environmental and social impacts [15].

From previous studies, it can be found that the balance of sustainable construction criteria can be viewed from the aspects of efficiency, financial feasibility, quality, and value of construction. By linking these sustainable aspects to the Regulation of the Minister of Public Housing of the Republic of Indonesia, Number 9 of 2021, which contains sustainable construction implementation guidelines, this study developed a sustainable lean performance indicator that is categorized into several criteria:

• Quality, health, safety, and environment;
• Sustainable design;
• End-user needs;
• Land management;
• Energy and water efficiency and conservation;
• Performance and material resource efficiency;
• Environmentally friendly materials usage;
• Sustainable management.

2.2. Sustainable Road Infrastructure

Infrastructure is a device that performs the function of initiating changes in economic variables, such as changes in company costs and home utility costs [16]. Roads are one form of transportation-related infrastructure that has the function of connecting two or more points. Road infrastructure has the function of connecting trip generation and attraction. Road infrastructure allows the community to provide services and mobility between communities, allowing movement in society [17].

The construction of road infrastructure has a large potential impact on the environment. A study carried out on the Cisumdawu toll road work conducted by Mulyana shows that CO₂e emissions produced per one kilometer of toll road can reach 2.4 million kg CO₂e [18]. Green infrastructure is one form of sustainable infrastructure implementation that adds value in the form of feasibility studies based on the impact of infrastructure development on biotic and abiotic ecosystems [19]. One form of sustainable construction implementation that can be achieved in infrastructure construction is the addition of sustainability criteria in the cradle-to-grave concept used in the project [20]. In addition, value management with planning, identification, analysis, creativity, evaluation, and development could result in enhanced value of construction output [21].

2.3. Sustainable Lean Construction

The lean principle is production management to maximize the value of the product that will be given to end-users and minimize waste at production stages to increase productivity [22]. Lean principles can also mean producing products by carrying out the production process at the right place, location, time, and quantity [23].

Lean construction is one form of implementing lean principles into sustainable concepts in the construction industry. Lean principles that are integrated into sustainable construction can produce principles and tools that can be developed into methods and technologies that can encourage the concept of sustainability in construction [6]. By integrating lean concepts into sustainable construction to become sustainable lean construction (SLC), efficiency, reduction, and optimization of value can be achieved in line with sustainability concepts. In addition, by incorporating sustainable lean construction into infrastructure projects, a reduction in waste and negative environmental impacts can be achieved at a more reasonable cost [24]. Previous study shows that lean principles can be integrated into sustainable construction by using Last Planner System (LPS), Value Stream Mapping (VSM), Standardized Work, The 5S process, Continuous Improvement in the form of Kaizen, Total Quality Management (TQM), Visualization, Fail Safe for Quality and Safety, Daily Huddle Meetings, The Five Whys, Just in Time (JIT), (Mathematics Collaborative Educational System (PCMAT), Concurrent Engineering, Kanban framework agile implementation, Poka-yoke (Mistake proofing technique), Target Value Delivery (TVD), Partnering, Total Productive Maintenance (TPM), and Computer-Aided Design ( CAD) dan Six Sigma [25].

Integrating lean principles into sustainable construction requires a framework that links lean principles to sustainability principles in construction projects [26]. Various lean construction tools that are currently in use in Indonesia are PERT (Program Evaluation and Review Technique) in project scheduling, the Last Planner System, Value Stream Mapping (VSM), Kaizen, and Just in Time (JIT) [27]. Although various lean tools have been used, the level of readiness of contractors in Indonesia to use lean construction concepts and tools is still quite low, where cycle time reduction and variability are the two variables with the lowest level of readiness [7]. This is added by a previous study showing that private construction companies have a negative perception of lean construction [28]. This level of awareness and readiness will affect the level of stakeholder engagement in lean construction implementation. This will be further investigated in this study.

2.4. Stakeholder Management

Stakeholders are parties (individuals, groups, or organizations) that can influence and be influenced by decisions, activities, or outcomes of a project, program, or portfolio [1]. Stakeholder management is a process of identifying the people or organizations that affect or are affected by the project, analyzing their expectations and engagement in the project, and developing effective strategies to engage stakeholders [29].

In a study conducted by Bal [30], six processes needed to be carried out by stakeholders to achieve sustainable construction. It consists of identifying key stakeholders, relating stakeholders to sustainability, prioritizing stakeholders, managing stakeholders, measuring sustainability performance, and putting targets into action. Previous studies explain that sustainable lean construction enables interaction and integration of technology and knowledge between designers and contractors [6].

Infrastructure projects have a high diversity of stakeholders. The stakeholder engagement is spread across the various life cycles of infrastructure development and operations. The greater the cost of the infrastructure project, the more complex the stakeholder engagement [31]. In implementing sustainable lean construction, the organizations involved can be generalized into government agencies, owners, contractors, planning consultants, architects, suppliers, project investors, and non-governmental organizations (NGOs). In many toll road infrastructure projects that require joint ventures between the government and private companies, it is necessary to analyze the investors of these companies in the decision-making process of implementing sustainable lean construction. These stakeholders are discussed further in this study because they have a direct relationship to the project in the decision-making process. Project-affected parties, such as the community and road users, are considered by the contractor in the decision-making process.

Stakeholder identification is the first process in stakeholder management, which is carried out by identifying parties involved in the project who need to be managed. The output from this stakeholder identification process is the stakeholder register, which contains stakeholder information held by the stakeholder. The stakeholder register also contains the classification of stakeholders that can be formed into stakeholder grids in the form of power–interest, interest–influence, and impact–influence. The stakeholder management plan is then added in the form of a stakeholder engagement assessment matrix, which contains the current level of stakeholder engagement and the desired level of stakeholder engagement that will determine the strategies needed to successfully implement sustainable lean construction. This paper will contribute to the improvement of SLC through stakeholder engagement strategies.

3. Research Methodology

This study was conducted using a variety of qualitative and quantitative methods to achieve the research objectives. A literature study was conducted at the beginning of this study to provide a theoretical basis for the research and identify the variables used in this study.

The first stage involved the literature study, variable validation, and the identification of stakeholders and their roles in sustainable lean construction. This stage was conducted to ensure that the variables tested met the needs of this research. At this stage, data were also collected in the form of the primary roles of stakeholders in implementing SLC. This stage was conducted through a review of 25 studies carried out in the last decade. From the literature review and validation interviews, there were 37 barriers, 30 driving factors, and 31 potential strategies to improve stakeholder engagement in SLC implementation, as shown in

Table 1. Driving factors of sustainable lean construction implementation.

Criteria	Drivers	Source
QHSE	Improved occupational health and safety	[32,33]
	Achieving continuous improvement	[33,34]
Sustainable Design	Creation of product innovation and certification	[3,33,35]
	Availability of eco-friendly energy technology	[32,33]
	Established a collaborative environment in the development of lean and sustainability concepts	[33,36]
	Integrated building design with BIM (Building Information Modeling)	[30,35]
	Improved level of implementation and design quality of lean and sustainable principles in infrastructure	[33,34]
End-User Needs	Focused on meeting the needs, interests, and goals of stakeholders	[2,33]
	Increased end-user awareness and knowledge of sustainability	[3,33,35]
	Market attraction to green construction	[33,37]
	Created an environment of collaboration and effective two-way communication	[2,33,36]
Land Use	Improved land use efficiency	[32,33]
	Decreased impact on ecosystem around the project	[33,34]
Energy and Water Efficiency	Reduction of energy consumption and project waste	[3,32,35]
Performance and Material Resource Efficiency	Improved efficiency and conservation of energy and water used in the project	[33,38]
	Improved efficiency and conservation of materials used in the project	[3,32,35]
	Reduction of work and procurement waiting time waste	[33,38]
	Improved time efficiency by standardizing manufacturing, procurement, and production processes	[2,33]
	Improving vendor cooperation throughout the project lifecycle	[3,33,35]
	Resource and environmental conservation	[33,38]
Environmentally Friendly Materials Usage	Improved safety and quality in the use of prefabrication	[2,33]
	Increased competitiveness in the sustainable construction material manufacturing industry	[3,33,35]
	Better methods of measuring sustainability costs	[3,33,35]
	Proactive role in material production	[33,34]
Sustainable Management	Reduced frequency of leadership conflicts within the company	[2,33]
	Increased awareness and responsibility for the project	[32,33]
	Improved company reputation	[3,33,35]
	Utilized standards and contracts are based on sustainability performance.	[3,32,35]
	Enable new collaborations and work integration between stakeholders	[32,33]
	Reduction in life cycle cost	[32,33]

,

Table 2. Barriers to implementing sustainable lean construction.

Criteria	Barriers	Source
QHSE	Lack of planning for quality in sustainable design	[39]
	Increased risk and uncertainty	[40]
	Lack of continuous quality assessment and management	[41]
Sustainable Design	Sustainable design lacks comprehensiveness, innovation, completeness, and applicability	[39,40,42]
	Lack of use of sustainable technologies	[17,41,43]
	Lack of consultant involvement in lean construction planning	[41]
	Lack of involvement of sustainability and lean concept experts in the design process	[9,17]
	Lack of visual representation of lean construction implementation demonstration	[32]
	Lack of knowledge and ability to use the principles and implementation of sustainable construction and lean principles	[3,41,43]
End-User Needs	There is no end-user satisfaction measurement	[9,17]
	Lack of understanding of end-user needs and lack of end-user focus	[9,17,39]
	Lack of end-user awareness regarding sustainability	[40]
	Lack of owner knowledge in sustainable design development	[3,35]
	Lack of demand and interest from end-users to use sustainable design	[32,40,44]
	Lack of client involvement in lean construction planning	[41]
Land use	Improving the project’s land use and ecosystem will increase costs	[45]
Energy and Water Efficiency	Lack of waste management planning	[45]
Performance and Material Resource Efficiency	Failure to achieve efficiency in operations	[9,17,41]
	Lack of performance (inefficiency) of procurement implementation	[41]
	Increased duration of work execution	[39,41]
	Delay in material delivery	[3,35,40]
	Lack of standardization of construction work	[39]
	Production process inefficiencies due to unclear sustainability attributes	[9,17]
	Lack of long-term relationships with suppliers	[9,17]
	Inefficiency in material utilization and resource management	[9,17,39]
Environmentally Friendly Materials Usage	Lack of knowledge and pre-fabrication implementation techniques	[9,17,41]
	Lack of availability of green suppliers, green materials, and sustainable materials	[43]
	Sustainable material prices tend to be higher	[32,35,40]
	Lack of supplier engagement in sustainable design	[3,35,44]
	Delay in supplier participation in sustainable material planning	[9,17]
Sustainable Management	Management and stakeholder resistance to change to sustainability implementation	[41]
	Lack of awareness, interest, motivation, and lack of proactive and responsive attitude	[39,40,43]
	Lack of support and commitment from management and owners	[39,40,41]
	Lack of regulations, incentives, and government support	[39,41,42]
	Unclear description of sustainability in the project and lack of company performance in the sustainability assessment	[32,42,44]
	Poor work integration between owner, consultant, and contractor	[3,9,17,35]
	Sustainability concepts increase project investment costs and increase the payback period	[9,35,42]

and

Table 3. Potential strategies to improve stakeholder engagement in implementing SLC.

Criteria	Potential Strategy	Source
QHSE	Engage stakeholders in the creation of integrated quality and risk management plan that is adaptive to change.	[33,40]
	Improve project management and focus on controlling the work process using Total Quality Management (TQM).	[33,34]
Sustainable Design	Project teams should be directed to use VSM and Value Engineering to create innovative and value-added projects using sustainable technologies.	[33,36]
	Appointed a green-certified manager to increase the engagement of consultants and experts by leading the collaborative development of sustainable concepts.	[33,40]
	Enhance collaboration between stakeholder groups and project teams to develop integrated building designs using BIM.	[33,46]
	The organization needs to establish a joint development and training system with other stakeholders.	[33,36]
End-User Needs	Develop a standardized measurement of stakeholders’ needs, interests, and understanding of the implementation of sustainable lean construction.	[33,36]
	Communicating VSM in lean construction to owners and end-users	[33,38]
	Collaboratively develop a plan for the implementation of continuous innovation in the project by the project team and owner.	[33,40,47]
	Generating sustainability demand in the construction industry	[33,40]
	Preliminary and detailed discussion of ideas, problems, and stakeholder needs	[33,46]
Land Use	Develop an integrated green open space use plan for road infrastructure areas that can be standardized in regulations.	[3,33,35]
Energy and Water Efficiency	Develop a multi-stakeholder integrated waste management system	[33,46]
Performance and Material Resource Efficiency	Improve productivity of project manpower and stakeholders through training, selection, and certification.	[33,34]
	Develop standardized SLC procedures for construction operations	[33,34]
	Stakeholders provide support by facilitating the project to run in a timely and effective manner.	[2,33]
	Standardize procurement at the work package level and regulate the use of tools between work packages.	[33,38]
	Use Lean Tools VSM (Value Stream Mapping) to reduce waste	[33,38]
	Utilize long-term procurement contracts to maximize benefits between stakeholders.	[2,33]
	Create a matrix of material and resource usage for each stakeholder	[33,47]
Environmentally Friendly Materials Usage	Organizations need to establish a sustainable construction method knowledge management system	[33,36]
	Develop regulation and standardization of eco-friendly construction materials	[33,46]
	Increase incentives given to stakeholders to conduct research development in sustainable materials.	[33,46]
	Provide sustainable design advice and input to project executors	[33,46]
	Suppliers should adapt the role of specialized contractors to form new types of contracts with stakeholders.	[3,33,35]
Sustainable Management	Develop tailored VSM with lean tools in construction projects	[33,38]
	Develop managerial procedures on SLC	[33,36]
	Develop and strengthen more comprehensive regulations on sustainable construction and lean construction.	[33,40]
	Improve planning quality through collaborative communication using BIM	[33,34]
	Maintaining consistent communication combined with continuous improvement of change orders from new stakeholders.	[33,36]
	Reducing financial burdens to sustainable projects and developing LCCs.	[33,40]

. Semi-structured interviews were then used with three experts in sustainable and lean construction.

The second stage involved a pilot study with 10 respondents, with criteria that were adjusted for the potential respondents in the third stage. This step was used to improve the quality of the questionnaire and ensure that it followed the objectives of this research.

The third stage involved a questionnaire survey in obtaining data on the level of influence, level of engagement, and strategies, which were analyzed using Fuzzy AHP and Fuzzy TOPSIS. Purposive sampling was used to select and filter the questionnaire respondents to ensure this study was relevant to the actual condition. The criteria chosen were that respondents should have at least a two-year’s experience in the construction industry and have participated in or conducted research on projects involving sustainable construction or lean construction.

Questionnaires that had been refined in the pilot study were distributed to 229 stakeholders via email, mail, and social media, and 61 were returned, resulting in a total response rate of 26.64%, as shown in

Table 4. Response rate.

Stakeholder Group	Questionnaires		Percentage Return (%)
	Sent	Returned
Owner	47	11	23.40%
Contractor	92	22	23.91%
Consultant	39	10	25.64%
Architect	18	3	16.67%
Government	34	7	20.59%
Supplier	23	6	26.09%
Other	14	2	14.29%
Total	267	61	22.85%

. Respondents’ profiles are shown in Figure 1.

The level of influence was analyzed using power, interest, impact, and engagement levels processed using the Certainty Index (CER). CER was calculated by summing the ownership of attribute weights for each stakeholder and then dividing by the sum of the data. The following formula is used:

$${\mathrm{C}\mathrm{E}\mathrm{R}}_A\left(G_i\right)=\frac{O_A^{+}}{N}$$

(1)

Via the same method, the level of engagement was analyzed to form a stakeholder engagement assessment matrix using the certainty index (CER). The attribute level was assigned to each stakeholder who had a CER value of more than 0.5.

Analysis using the Relative Importance Index (RII), as in

$$\mathrm{R}\mathrm{I}\mathrm{I}=\frac{\sum W}{(A\times N)}$$

(2)

was also used in the third stage to obtain the relative importance of the driver and barrier factors on the implementation of sustainable lean construction by stakeholders in road infrastructure projects. RII was calculated based on a Likert scale of 1–5 and involved the weight value of each factor divided by the largest value of the respondent.

Further analysis using Fuzzy AHP and Fuzzy TOPSIS was performed in the third stage to obtain the most ideal and ranked strategy by reviewing the fulfillment of stakeholder satisfaction level, demand, and cooperation criteria. The fuzzy analysis begins with weighing stakeholder satisfaction level, demand, and cooperation using Fuzzy AHP. The stakeholder satisfaction, demand, and cooperation weighting data were entered into a pair-wise comparison matrix. To get a pair-wise comparison matrix, data input is required in the criteria columns and rows. The process is continued by creating a pairwise comparison, calculating the geometric mean, calculating fuzzy weights, and finding the center of the area (COA). The fuzzy analysis continued using Fuzzy TOPSIS to analyze potential strategy scenarios against stakeholder satisfaction, demand, and cooperation that have been weighted using Fuzzy AHP. The level of suitability of the strategy for stakeholders was assessed according to Fuzzy rules and treated as a random variable.

The Fuzzy calculation of the coefficient of closeness CCi to all alternative scenarios was calculated with Fuzzy TOPSIS. The CCi value was the basis for ranking the scenario alternatives for potential stakeholder engagement strategies in this study. Then, the relationship between inhibiting factors and strategies to improve stakeholder engagement was analyzed. This correlation analysis was carried out using the Spearman test to assess whether the potential strategies that have been assessed and evaluated using fuzzy logic can address the barriers to implementing sustainable lean construction. The results of the Spearman correlation test determined the shape of the flowchart between the barriers and the development of strategies to increase stakeholder engagement.

The fourth stage was carried out with semi-structured interviews to validate the result of this study and navigate through the analysis process of the study findings. Validation of the study results was conducted using semi-structured interviews with three experts in sustainable and lean construction.

4. Results

From the literature review and semi-structured interviews, 10 stakeholder groups were identified as having high influence and engagement in the implementation of SLC in the construction industry. These stakeholders are owners, contractors, subcontractors, architects, suppliers, the central governments, the local government, project investors, and NGOs. The results of the semi-structured interviews on stakeholder roles in SLCs were quantified, classified, and summarized into key stakeholder roles in SLC implementation, as shown in

Table 5. Stakeholder roles in sustainability.

Stakeholders	Roles in Sustainability
Owner	Stimulator
Contractor	Context-Enabler
Sub-Contrator	Context-Enabler
Consultant	Concept-Refiner
Architect	Concept-Refiner
Supplier	Provider
Central Government	Regulator
Local Government	Regulator
Project Investor	Initiator
NGO	Concept-Refiner

.

4.1. Stakeholder Influence and Engagement Level in Implementing SLC

The results of the level of influence and level of engagement obtained from 61 valid respondents were processed using the certainty index (CER) to obtain the level of power, interest, impact, influence, and level of engagement. The mean value of each level of influence obtained from respondents was tested for CER value.

The vested levels were given to each stakeholder who had a CER value > 0.5.

Table 6. The level of Power, Interest, and Influence that stakeholders possess in sustainable lean construction.

Stakeholder	Power		Interest		Influence
	Level	CER	Level	CER	Level	CER
Owner	5	0.721	4	0.525	5	0.770
Contractor	4	0.639	4	0.508	4	0.689
Sub-Contrator	3	0.639	3	0.508	4	0.574
Consultant	4	0.689	4	0.508	4	0.557
Architect	3	0.557	4	0.525	4	0.508
Supplier	3	0.508	3	0.508	3	0.541
Central Government	4	0.541	4	0.574	4	0.508
Local Government	4	0.574	3	0.541	4	0.525
Project Investor	3	0.508	3	0.590	4	0.541
NGO	2	0.574	2	0.508	2	0.557

summarizes the results of power, interest, influence, and engagement levels that meet a CER value > 0.5. These values are as follows: 5 = very high; 4 = high; 3 = low; 2 = very low; and 1 = minimum.

Table 7. Stakeholders’ current and desired level of engagement on the implementation of sustainable lean construction.

Stakeholder	Current		Desired
	Level	CER	Level	CER
Owner	4	0.508	5	0.820
Contractor	4	0.557	5	0.820
Sub-Contrator	3	0.607	4	0.590
Consultant	4	0.508	5	0.656
Architect	4	0.541	4	0.541
Supplier	3	0.557	4	0.590
Central Government	4	0.508	5	0.607
Local Government	4	0.590	5	0.525
Project Investor	4	0.508	4	0.557
NGO	3	0.508	4	0.590

summarizes the results of the level of engagement, where the values are as follows: 5 = leading; 4 = supportive; 3 = neutral; 2 = resistance; and 1 = unaware.

The level of influence obtained was inserted into the power–interest grid, interest–influence grid, and impact–influence grid, as shown in Figure 2. The three stakeholder grids determine the type of strategy that needs to be undertaken to increase stakeholder engagement in the SLC.

The current level of engagement represents the existing condition of perception and willingness to involve the stakeholder group in the decision-making process for sustainable lean construction implementation. The desired level of engagement represents the level of engagement that the stakeholder group is expected to have. The desired level of involvement will be the target level in determining the strategies that the company can use to increase stakeholder engagement.

The level of engagement obtained from the certainty index is then formed into a stakeholder engagement assessment matrix.

Table 8. CER value of stakeholder engagement in sustainable lean construction.

Stakeholders	Unaware	Resistance	Neutral	Supportive	Leading
Owner				C	D
Contractor				C	D
Sub-Contrator			C	D
Consultant				CD
Architect			C	D
Supplier				C	D
Central Government				C	D
Local Government				C	D
Project Investor				CD
NGO			C	D

Note: The symbol (C) represents the current level of stakeholder engagement, and the symbol (D) represents the desired level of stakeholder engagement. If the C and D levels are at the same level (CD), then the desired level of stakeholder engagement has been achieved.

is a form of stakeholder engagement assessment matrix on the implementation of SLC for stakeholders. The level of influence and level of engagement were summarized in a stakeholder register.

Table 9. Stakeholder engagement assessment matrix in sustainable lean construction.

No	Stakeholder	Internal-External	Role in Sustainable Construction	Power-Interest	Interest-Influence	Impact-Influence	Current Engagement Level	Desired Engagement Level
1	Owner	Internal	Stimulator	Manage Closely	Collaborate	Dialogue	Supportive	Leading
2	Contractor	Internal	Context Enabler	Manage Closely	Collaborate	Dialogue	Supportive	Leading
3	Sub-Contrator	Internal	Context Enabler	Monitor	Involve	Consultation	Neutral	Supportive
4	Consultant	Internal	Concept Refiner	Manage Closely	Collaborate	Dialogue	Supportive	Leading
5	Architect	Internal	Concept Refiner	keep Informed	Collaborate	Consultation	Supportive	Supportive
6	Supplier	Internal	Provider	Monitor	Inform	Information Gathering	Neutral	Supportive
7	Central Government	External	Regulator	Manage Closely	Collaborate	Dialogue	Supportive	Leading
8	Local Government	External	Regulator	Keep Satisfied	Involve	Dialogue	Supportive	Leading
9	Project Investor	External	Initiator	Monitor	Involve	Consultation	Supportive	Supportive
10	NGO	External	Concept Refiner	Monitor	Inform	Information Gathering	Neutral	Supportive

summarizes the stakeholder register on the role, level of influence, and level of stakeholder engagement in SLC.

4.2. Rank of Barriers and Drivers Preceived by Stakeholders on SLC Implementation

The results of the 61 respondents’ assessment of the barriers and drivers of SLC implementation in road and bridge infrastructure were processed using the Relative Importance Index (RII) to obtain a relative ranking of the barriers and drivers.

Table 10. SLC implementation barrier ranking.

Barrier	RII	Rank
Lack of knowledge and ability to use the principles and implementation of sustainable construction and lean principles	0.875	1
Lack of support and commitment from management and owners	0.859	2
Lack of awareness, interest, motivation, and lack of proactive and responsive attitude	0.852	3
Sustainable material prices tend to be higher	0.849	4
Lack of regulations, incentives, and government support	0.849	5
Sustainable design lacks comprehensiveness, innovation, completeness, and applicability	0.823	6
Lack of use of sustainable technologies	0.820	7
Lack of demand and interest from end-users to use sustainable design	0.816	8
Lack of owner knowledge in sustainable design development	0.813	9
Management and stakeholder resistance to change to sustainability implementation	0.810	10
Lack of standardization of construction work	0.807	11
Lack of availability of green suppliers, green materials, and sustainable materials	0.800	12
Lack of visual representation of lean construction implementation demonstration	0.797	13
Inefficiency in material utilization and resource management	0.784	14
Production process inefficiencies due to unclear sustainability attributes	0.780	15
Lack of planning for quality in sustainable design	0.777	16
Lack of performance (inefficiency) of procurement implementation	0.774	17
Increased duration of work execution	0.774	17
Lack of continuous quality assessment and management	0.770	19
Failure to achieve efficiency in operations	0.767	20
Lack of knowledge and pre-fabrication implementation techniques	0.767	21
Lack of waste management planning	0.764	22
Unclear description of sustainability in the project and lack of company performance in the sustainability assessment	0.764	23
Increased risk and uncertainty	0.761	24
Delay in material delivery	0.754	25
Lack of involvement of sustainability and lean concept experts in the design process	0.751	26
Poor work integration between owner, consultant, and contractor	0.751	27
Lack of consultant involvement in lean construction planning	0.748	28
Lack of client involvement in lean construction planning	0.744	29
Sustainability concepts increase project investment costs and increase the payback period	0.721	30
Lack of end-user awareness regarding sustainability	0.715	31
Improving the project’s land use and ecosystem will increase costs	0.702	32
Lack of understanding of end-user needs and lack of end-user focus	0.698	33
There is no end-user satisfaction measurement	0.692	34
Delay in supplier participation in sustainable material planning	0.692	35
lack of supplier engagement in sustainable design	0.682	36
Lack of long-term relationships with suppliers	0.630	37

summarizes the ranking of barriers to SLC implementation.

Table 11. SLC implementation drivers ranking.

Driving Factor	RII	Rank
Improved time efficiency by standardizing manufacturing, procurement, and production processes	0.895	1
Improved level of implementation and design quality of lean and sustainable principles in infrastructure	0.892	2
Achieving continuous improvement	0.889	3
Reduction of work and procurement waiting time waste	0.882	4
Reduction in life cycle cost	0.875	5
Improved efficiency and conservation of materials used in the project	0.852	6
Established a collaborative environment in the development of lean and sustainability concepts	0.846	7
Reduction of energy consumption and project waste	0.843	8
Improved occupational health and safety	0.836	9
Improved efficiency and conservation of energy and water used in the project	0.833	10
Integrated building design with BIM (Building Information Modeling)	0.830	11
Utilized standards and contracts are based on sustainability performance.	0.823	12
Market attraction to green construction	0.820	13
Created an environment of collaboration and effective two-way communication	0.813	14
Resource and environmental conservation	0.800	15
Improved company reputation	0.797	16
Enable new collaborations and work integration between stakeholders	0.797	17
Creation of product innovation and certification	0.793	18
Better methods of measuring sustainability costs	0.770	19
Focused on meeting the needs, interests, and goals of stakeholders	0.767	20
Availability of eco-friendly energy technology	0.764	21
Increase end-user awareness and knowledge of sustainability	0.761	22
Improved land use efficiency	0.761	22
Improving vendor cooperation throughout the project lifecycle	0.754	24
Improved safety and quality in the use of prefabrication	0.754	24
Increased awareness and responsibility for the project	0.751	26
Proactive role in material production	0.741	27
Increased competitiveness in the sustainable construction material manufacturing industry	0.711	28
Reduced frequency of leadership conflicts within the company	0.679	29
Decreased impact on ecosystem around the project	0.675	30

summarizes the ranking of drivers for stakeholders to implement SLC.

4.3. Strategies for Increasing Stakeholder Engagement

Based on the weighting and assessment of 61 respondents on stakeholder demand, satisfaction, and cooperation, weighting was carried out using fuzzy AHP.

Table 12. Fuzzy AHP weighting.

Attribute	Weight
Stakeholder Demand	0.308
Stakeholder Satisfaction	0.340
Stakeholder Cooperation	0.352

summarizes the weight values between stakeholder demand, satisfaction, and cooperation that will be used in the fuzzy TOPSIS calculation.

The respondents’ assessments of potential strategies to increase stakeholder engagement in SLC were analyzed using fuzzy TOPSIS with the weights obtained from fuzzy AHP. Each potential strategy scenario was assessed against stakeholder satisfaction, demand, and cooperation to find the positive ideal solution and the negative ideal solution to get the CCi coefficient value, which was the basis for ranking the fuzzy values.

Table 13. SLC implementation stakeholder engagement strategy ranking.

Strategy	Fuzzy Score	Fuzzy Rank	Priority
Develop regulation and standardization of eco-friendly construction materials	0.750	1	Extensive
Improve productivity of project manpower and stakeholders through training, selection, and certification	0.740	2	Extensive
Increase incentives given to stakeholders to conduct research development in sustainable materials.	0.730	3	Extensive
Project teams should be directed to use VSM and Value Engineering to create innovative and value-added projects using sustainable technologies.	0.713	4	Extensive
Use Lean Tools VSM (Value Stream Mapping) to reduce waste	0.667	5	Extensive
Develop tailored VSM with lean tools in construction projects	0.608	6	Major
Communicating VSM in lean construction to owners and end-users	0.603	7	Major
Develop and strengthen more comprehensive regulations on sustainable construction and lean construction.	0.510	8	Major
Develop a multi-stakeholder integrated waste management system	0.459	9	Major
Improve project management and focus on controlling the work process using Total Quality Management (TQM).	0.397	10	Moderate
Develop a standardized measurement of stakeholders’ needs, interests, and understanding of the implementation of sustainable lean construction.	0.394	11	Moderate
Develop standardized SLC procedures for construction operations	0.373	12	Moderate
Stakeholders provide support by facilitating the project to run in a timely and effective manner.	0.342	13	Moderate
The organization needs to establish a joint development and training system with other stakeholders.	0.322	14	Moderate
Enhance collaboration between stakeholder groups and project teams to develop integrated building designs using BIM	0.316	15	Moderate
Standardize procurement at the work package level and regulate the use of tools between work packages.	0.309	16	Moderate
Preliminary and detailed discussion of ideas, problems, and stakeholder needs	0.286	17	Minor
Improve planning quality through collaborative communication using BIM	0.285	18	Minor
Maintaining consistent communication combined with continuous improvement of change orders from new stakeholders.	0.283	19	Minor
Develop managerial procedures on SLC	0.281	20	Minor
Collaboratively develop a plan for the implementation of continuous innovation in the project by the project team and owner.	0.254	21	Minor
Engage stakeholders in the creation of integrated quality and risk management plan that is adaptive to change.	0.253	22	Minor
Generating sustainability demand in the construction industry	0.242	23	Minor
Organizations need to establish a sustainable construction method knowledge management system	0.228	24	Minor
Appoint a green-certified manager to increase the engagement of consultants and experts by leading the collaborative development of sustainable concepts.	0.225	25	Minor
Create a matrix of material and resource usage for each stakeholder	0.212	26	Minor
Utilize long-term procurement contracts to maximize benefits between stakeholders.	0.195	27	Minor
Reducing financial burdens to sustainable projects and developing LCCs	0.187	28	Minor
Develop an integrated green open space use plan for road infrastructure areas that can be standardized in regulations.	0.171	29	Minor
Provide sustainable design advice and input to project executors	0.162	30	Minor
Suppliers should adapt the role of specialized contractors to form new types of contracts with stakeholders	0.008	31	Low

summarizes the ranking of strategies that can be implemented by stakeholders. The priority of this strategy is determined by categorization using the standard deviation and mean value of the fuzzy value, where the fuzzy value is categorized by the interval of the mean value added by a multiple of the standard deviation. Strategies with fuzzy values above 0.664 have extensive priority; fuzzy values between 0.664 and 0.477 have major priority; fuzzy values between 0.477 and 0.29 have moderate priority; fuzzy values between 0.29 and 0.103 have minor priority, and values below 0.103 have low priority. This prioritization is important so that stakeholders can consider the strategy from the level of impact generated.

The fuzzy logic-analyzed strategies were analyzed using Spearman correlation to determine whether these strategies address the perceived barriers to the implementation of sustainable lean construction in Indonesian road infrastructure. The results showed a fairly strong relationship, with a spearman’s rho value of 0.002 and a correlation coefficient of 0.497. With the fulfillment of a significance value of less than 0.005 and a correlation coefficient value that was in a strong enough category, the strategy is able to answer the problems encountered by stakeholders. Therefore, a flowchart for developing a strategy to increase stakeholder engagement in SLC adapted from the principle of continuous improvement can be found in Figure 3.

5. Discussion

5.1. Stakeholder Influence and Engagement in SLC

The project owner has an engagement gap, in which there is a difference between the current level of engagement and the expected level of engagement. Currently, the owner has a supportive level, which includes supporting any kind of SLC implementation on the road and bridge projects. However, the owner needs to increase the engagement level to lead the implementation of sustainable lean construction on the project. The engagement types that need to be performed toward the owner are managed closely through collaboration and dialogue. To maintain and improve the owner’s level of engagement, an engagement strategy with joint collaboration on lean design and management systems with other stakeholders is required. The need for this level of involvement is supported by research conducted by Kim [48], where the owner’s initiative determines the implementation of SLC, although the form of engagement required has not been further described.

The contractor has an engagement gap. Currently, contractors have a supportive level of engagement in implementing sustainable construction. Contractors have not been able to achieve the desired level of engagement because the decision-making process for implementing sustainable lean construction still focuses on the owner. A previous study shows that the “partnership relationship” in lean construction with the project owner has an importance level of 80% but ease of implementation level of 26% [49]. Contractors have a great influence on the implementation of sustainable lean construction. The forms of engagement that contractors have are managing closely, collaboration, and dialogue. Regular interaction is needed in the contractor team and intensive collaboration from the project initiation to the completion of construction implementation.

Subcontractors have an engagement gap. Currently, subcontractors have a neutral level of engagement. This indicates that subcontractors on road projects have not yet considered planning and implementing lean construction systems and tools. Subcontractors can focus on developing lean and sustainable tools that are suitable for one type of contracted work package. Subcontractors have low power and interest but have a high level of influence in the implementation of sustainable lean construction. It is necessary to create a communication plan by involving subcontractors and conducting focused consultations on work packages connected to subcontractors. This result is supported by Yen [50], where subcontractors can develop lean-focused tools, such as LSPP (Lean Subcontraction Procurement Process), to increase efficiency and improve communication performance with contractors.

Consultants have an engagement gap. The current level of supportive engagement means that consultants support lean construction with a limited role in decision-making regarding the development of lean tools that can be used in road projects. Consultants have a high level of power, interest, and influence, so they have to be engaged with managing closely, collaboration, and dialogue. To increase the level of engagement in sustainable lean construction in road infrastructure, intensive collaboration and communication between consultants, architects, contractors, and owners are needed to meet the sustainability criteria of each stakeholder. A previous study also found that consultants and architects have a role in the creation of sustainable design and the necessity of integrated collaboration with the owner [51].

Architects are one of two stakeholders who do not have an engagement gap. Architects have a low level of power and influence but a high level of interest and influence. In the stakeholder engagement plan, architects have to be engaged with keeping informed, collaborating, and consulting. Architects play an important role in planning sustainable lean construction stakeholder engagement and must collaborate in shaping sustainable design. In addition, it is necessary to consult the created design and provide information regarding the execution of the design, whether it is in accordance with the planned design or not.

Suppliers have an engagement gap. Currently, suppliers have a neutral level of engagement in the application of sustainable lean construction to road projects. The engagement gap gives the impression that the supplier’s sustainability improvement efforts have an insignificant impact on SLC. In stakeholder engagement planning, suppliers have a low level of power, interest, and influence. Sustainable performance information on materials and tools provided by suppliers can be useful information to management in determining the level of implementation of sustainable lean construction in road infrastructure projects. Previous studies found that to improve project sustainability performance, suppliers had to improve the transparency of the environmental performance of specific manufacturing processes [52].

The Central Government has an engagement gap. The engagement gap in the central government indicates that the government is not fully prepared to implement sustainable construction, lean construction, and sustainable lean construction in Indonesia. These results are supported by Sarli [53], which shows that incentives have not been well implemented in Indonesia, and there is no standard for calculating incentives. The government has to be engaged with managing closely, collaboration, and dialogue. The government and key project stakeholders, such as owners and contractors, are expected to develop regulations to implement sustainable lean construction in road infrastructure.

The local government has an engagement gap. The local government currently mainly prioritizes the primary needs of stakeholders and has not focused on sustainability. Local government needs to be engaged with keeping satisfied, involving, and having a dialogue. In improving local government engagement, project management needs to consider the needs and things desired by local governments to meet local government satisfaction. The expert also stated that there is a need for dialogue and collaboration with the central government in order to mobilize local governments.

Project investors are stakeholders who do not have an engagement gap. Project investors, who have the role of initiator, initiate the concepts of sustainability, lean concept, and management to the owner. The initiation can be in the form of an investment to the owner. Investors have to be engaged in monitoring, involving, and consulting. To improve the investor’s engagement, it needs to be in the form of consultation on the concept of sustainability. Project managers can increase investor engagement by holding consultations and proposing sustainability aspects to investors.

NGOs have a neutral level of engagement and a desired level of engagement at the support level. NGOs have a neutral level of engagement because they have limited engagement in providing support in the form of campaigns and support for the implementation of sustainable lean construction. The engagement of NGOs in the implementation of sustainable lean construction is the provision of information related to the development, management systems, tools, and implementation of lean construction on road infrastructure projects in Indonesia.

5.2. Barriers to SLC Implementation

Lack of knowledge and ability to use the principles of sustainable construction and lean principles is the perceived barrier with the largest RII value. This proves that in road infrastructure, tools and methods for sustainable work and lean work methods have not been developed effectively enough to be applied to road infrastructure. This result is supported by Nwaki [41], where knowledge and technology barriers are the main constraining factors and will decrease stakeholder interest in implementing sustainable construction. This is also added by the expert, where the actual knowledge of lean principles and tools has increased, but the application to road infrastructure has not increased due to a lack of measurement procedures. The ability to standardize work packages and work volumes is a challenge for project planners and implementers because the topography of the project greatly determines the shape of the structure that the road project has.

Lack of management and owner support and commitment is the second highest-ranking barrier. This is supported by Nwaki [41], where leadership and management barriers are the second highest barriers after a lack of knowledge of lean construction. The lack of support and commitment to the implementation of lean construction causes the implementation to be less than optimal. This lack of support can be caused by the complexity of the sustainability and lean aspects of road infrastructure. This barrier shows that there is a need for commitment and support from various parties, especially management and various main contractors, to develop and create standards for contractors to implement lean tools on projects.

Lack of awareness, interest, motivation, and a proactive and responsive attitude toward sustainable lean construction is the third highest-ranking SLC barrier. The lack of awareness and interest among stakeholders is caused by the unclear benefits offered by the implementation of sustainable construction and lean construction. Profit-driven organizations usually refuse to use sustainable construction because it requires additional costs to improve the quality of teams capable of implementing sustainable construction. A previous study found that the lack of awareness among stakeholders is the highest inhibiting factor and causes a lack of education and training for workers [54].

The lack of regulations, incentives, and government support for the implementation of lean construction and sustainable construction is the fourth highest barrier. Research conducted by Alsanad [54] explains that the lack of incentives is the second highest inhibiting factor and greatly affects the willingness of stakeholders in the implementation of sustainable construction. Without clear standards, stakeholders will be limited regarding the sustainable scope that can be given to the project. One of these flaws is the lack of regulations governing the use of sustainable materials that can be used by contractors. The absence of incentives is another problem regarding the implementation of lean construction in Indonesia.

The price of sustainable materials, which tend to be higher than non-sustainable materials, is the fifth highest perceived barrier. The higher price of sustainable materials could be due to the high cost of research to develop sustainable materials. This is possible because the material options that can be used are limited by existing regulations in Indonesia. Durdyev [44] also emphasized the lack of sustainable options, which drove up the cost of sustainable construction.

5.3. Drivers of SLC Implementation

Increased time efficiency by standardizing the material processing, procurement, and production processes is the driving factor for stakeholders with the largest RII value. This demonstrates that increased time efficiency as a result of using lean tools on road infrastructure is the most motivating factor in road infrastructure projects. Waste reduction can be achieved by standardizing the construction production process. Standardization can be applied to road infrastructure in the same way that it can be applied to buildings, resulting in very high efficiency while reducing costs and time. This result is also added by Tokbolat [32], where the efficiency of resources and energy is the main driving factor for the implementation of sustainable construction for stakeholders.

Improved design quality through lean and sustainable principles in infrastructure is the second-highest driving factor in SLC. The structural and environmental quality of the design will be enhanced when the owner, planning consultant, and architect collaborate on a sustainable design. By creating urban planning integrated with green infrastructure planning, road infrastructure can be created that will improve the performance of the environment around the infrastructure, such as the creation of eco-ducts and eco-bridges between road infrastructure and buffer zone planning. This can be achieved along with the fulfillment of the functions to connect trip generation and improve social quality around the project. A previous study shows that improving the quality of design planning and environmental performance is a key driver for improving the use of lean construction to achieve continuous improvement [34].

Achieving continuous improvement is the third highest-driving factor. Continuous improvement enables the organization to learn continuously from experience gained in previous projects and best practices to achieve the best project output. Continuous improvement processes, namely,1§§ identification, planning, execution, and review, allow the formation of issue logs and current problems in the project to be reviewed and become organizational process assets for further project development. This is supported by Silva [23], where embedding the KAIZEN culture can improve the performance of managers and employees on a personal level.

Reduction of work and procurement waiting time waste is the fourth highest driving factor. Increased time efficiency can shorten construction time and increase the amount of floating time used for other work. This will certainly have a very positive impact on all stakeholders because it will provide new opportunities and new agreements. This indicates that the reduction of waiting time waste will help the project meet its KPIs and improve performance. Mudzakir [55] explains that waiting time for instructions, work, and materials to arrive is the most common waste on projects.

Reduction in life cycle cost is the fifth highest driving factor. Decreasing the operating cost of road infrastructure is a very important factor for stakeholders, especially the owner. As in the case of toll roads, a decrease in life cycle cost can enable an increase in the IRR value and a decrease in the payback period, which will certainly increase the benefits felt by the owner. A decrease in life cycle cost can also reduce stakeholder concern in implementing sustainable construction because of the increase in the initial cost. Durdyev [44] adds that improving value for money and lifecycle costs are key drivers in sustainable construction. This is supported by expert questions where the reduction of lifecycle costs can greatly affect decision-making, especially for owners and investors.

5.4. Strategies for Increasing Stakeholder Engagement

As shown in Figure 3, the flow starts with analyzing the level of influence and engagement that stakeholders have. Identifying barriers and drivers and developing potential strategies that can be used to assess whether the strategies are feasible to use. Prioritize, implement, measure, and evaluate the strategy’s performance. Then standardize processes and strategies that have excellent performance.

It was found that strategies related to the development of regulations and standardization of environmentally friendly materials have the highest fuzzy value and, hence, the highest priority. A previous study supported the finding that the main drivers of sustainability are technology and information, improved standards, and evaluation [56]. The central government, which has a primary role as a regulator, has a very important role in creating regulations and standardization of the application of lean construction, sustainable construction, sustainable materials, and design standards related to sustainable construction. The expert emphasized that the government plays a crucial role in establishing standards and guidelines for sustainable building, particularly with materials and equipment such as lean tools and others. The owner, who has a primary role as a stimulator, should create a form of cooperation with the government to develop new sustainability standards for massive road infrastructure projects.

The second highest-ranked strategy is increasing the productivity of project manpower through training, selection, and certification. According to Kim’s [48] research, lean tools will greatly improve the quality of manpower management, as well as improve stakeholder engagement and management commitment. To increase the level of stakeholder engagement in the implementation of sustainable lean construction on road projects, contractors and subcontractors should create KPIs and productivity improvement plans. Here, the owner has the role of providing financial support and incentives for the contractors to apply lean tools, such as KAIZEN, to continue improving productivity and stakeholder management performance. The lesson learned from the previous process can be an input for the next VSM productivity level development.

Increasing the incentives provided to stakeholders is the third most effective strategy for increasing stakeholder engagement. Incentives are one of the main driving factors for stakeholders to implement lean construction, sustainable construction, and sustainable lean construction. In road infrastructure, the government can provide progressive incentives for sections that have been implemented using sustainable materials and sustainable construction. Incentives for ongoing projects will enable project contractors to provide added value that can be utilized to utilize these incentives. In fact, incentives for initially starting projects will have a more substantial and stronger impact.

Adding value to the project, one of which uses Value Stream Mapping (VSM), is a strategy with fuzzy values with the fourth-highest rank. The existence of added value can create the new business potential that could generate profits and value for the road infrastructure. Physical added value to road infrastructure projects can be added, such as the addition of wind-powered electricity generators or solar panels for the operating period of elevated toll roads, providing electricity supply for the surrounding road infrastructure. It is added by Senay [57] that value engineering can be used to achieve cost reduction, time savings, quality improvement, and cost savings.

The use of lean tools VSM (Value Stream Mapping) to reduce waste is a strategy with the fifth-highest rank. Value Stream Mapping is a form of managing information, materials, and production processes to identify and eliminate waste along the value stream [24]. VSM is used to identify operation time, operation cost, manpower in operation, and schedule arrangements in each process in construction implementation. Utilizing VSM technologies, contractors and subcontractors may identify work execution process time, communication and management time, and waste reduction through value engineering.

6. Comparison with Previous Studies

The findings of this study show some similarities and differences with previous research. This study confirms the explanation by Li [58] about the level of stakeholder involvement measured using the Factor of Stakeholder Influence Level method, where government organizations and owners have a high level of influence and involvement. However, there are differences where Li [58] explains that the government has the highest rank of involvement and is followed by the owner. Using a different method, this study found that owners have a higher level of power, interest, and impact than government organizations. This shows that in applying lean concepts to sustainable construction, the owner has a higher role than when applying sustainable construction. Differences also exist in the level of involvement of designers, namely, consultants and architects, where Li explains that designers have a low level of influence in the application of sustainable construction. In this study, it was found that consultants and architects have a fairly high level of influence, proving that designers have a significant influence in integrating lean concepts into sustainable construction.

A previous study conducted by Eyiah [59] explained that in engaging stakeholders, identifying stakeholder needs and interests is performed. Unlike the previous study, this study uses a different approach by comparing the current engagement level with the desired engagement level to determine whether a stakeholder engagement improvement strategy is needed. The level of influence (power, interest, and influence) is used to determine the engagement strategy approach taken by stakeholders. This approach is used to ensure that the strategy is assessed in accordance with the desired engagement level of each stakeholder. This study explains that 8 out of 10 stakeholder groups analyzed have engagement gaps. With the existence of engagement gaps, driver and barrier analysis is used to form a stakeholder engagement improvement strategy that is adjusted to the stakeholder’s level of influence.

This study confirms the explanation given by Bajjou [60], where a lack of knowledge of lean construction practices is the main barrier to lean construction implementation. This study shows that the lack of lean construction knowledge is not only a general barrier to lean construction but also a barrier that is felt directly by many stakeholders. However, there are some differences in the findings of this study when compared to the barriers to sustainable construction implementation. Durdyev [44] and Ahn [35] explain that the main barrier to sustainable construction is the increase in the cost of sustainable design and sustainable building options. This study proves that the barrier to lean integration into sustainable construction, as perceived by stakeholders, is the limited ability of workers to develop lean construction tools and techniques in the project due to limited knowledge of lean construction that intersects with sustainable construction principles. The main barrier perceived by stakeholders is no longer in the form of financial barriers but in how to apply lean concepts to sustainable construction effectively and efficiently. Another finding is explained by Enshassi [61], where the main barrier to lean construction is poor leadership. Poor leadership possessed by stakeholder groups is caused by a lack of knowledge regarding the importance of lean construction and will cause resistance to change, which obstructs the process of developing lean concept knowledge in sustainable construction.

This study explains that improved time efficiency is the highest driver of SLC implementation. This confirms the explanation by Bajjou [60], where reducing construction cost and duration is the key driver of lean construction implementation. However, this efficiency is different from the efficiency that is the key driver in sustainable construction, where Tokbolat [32], Durdyev [44], and Ahn [35] explain that energy and resource efficiency are the key drivers of sustainable construction. This research proves that the integration of lean into sustainable construction will change the motivation of stakeholders to focus on time efficiency. Time efficiency will lead to greater resource efficiency, which will increase profits. This is supported by the study described by Pitt [15], where the financial aspect is the main driving factor for the implementation of sustainable construction.

In a study conducted by Gao [46], it was explained that the strategy to improve the implementation of lean construction for stakeholders who are not familiar with lean construction is introducing, educating, informing, convincing, and assisting stakeholders about lean construction. For stakeholders who are familiar with lean construction but are not implementing it, the appropriate strategies are highlighting positivity, analyzing approaches toward lean through computer modeling and simulation, and support from external facilitators or owners. Strategies for stakeholders who have implemented but have not achieved good results are hiring external consultants, developing collaborative delivery and performance-controlling system, using building information modeling, and selecting the most appropriate tools. These results are different from the findings in this study. The use of the stakeholder engagement matrix method in this study allows stakeholders to be assessed for their level of involvement, which resulted in 7 out of 10 stakeholders having a supportive engagement level. The findings explain that optimization of lean and sustainable construction implementation can be achieved by assessing strategies to improve stakeholder engagement with Fuzzy AHP and TOPSIS on important aspects related to stakeholders, namely stakeholder demand, satisfaction, and cooperation. This study presented the results about material standardization through regulation, improving productivity through training, increasing incentives given to implementers, and using lean tools such as VSM and Value engineering are the key strategies to improve sustainable lean construction implementation. The difference indicates that the identification of the level of stakeholder involvement and level of influence presented by this study will affect the appropriate strategy to improve the implementation of sustainable lean construction.

7. Conclusions

This paper shows that a total of 8 out of 10 stakeholders have an engagement gap between the current level of stakeholder engagement and the desired level of sustainable lean construction engagement in road and bridge infrastructure in Indonesia. Currently, the stakeholders with the highest level of engagement in sustainable lean construction are contractors, owners, the government, and consultants who have a supportive level of engagement. Meanwhile, NGOs have the lowest level of engagement at the neutral level. The highest inhibiting factor for the implementation of sustainable lean construction is the lack of knowledge and ability to use the principles and implement sustainable construction using lean principles. The highest driving factor for the implementation of sustainable lean construction is the increase in time efficiency that results from standardizing the processes of material management, procurement, and production. The highest-ranked strategies with extensive priority in improving stakeholder engagement on the implementation of sustainable lean construction on road infrastructure in Indonesia are developing regulations and standardization of environmentally friendly materials by the government with the support of the owner and increasing the productivity of project manpower and stakeholders through training, selection, and certification carried out by contractors and subcontractors.

The findings of this study contribute to the improvement of sustainable lean construction implementation through stakeholders’ engagement strategies. This study offers lean construction strategies that stakeholders can implement to improve the implementation of sustainable construction in road projects by considering the benefits offered by lean construction. This study also provides a perspective on the level of engagement in sustainable construction by each stakeholder that influences the decision-making process of road construction projects. The principle of continuous improvement can be used to increase stakeholder engagement in SLC strategy development. The government, as a stakeholder with a regulatory role, can develop comprehensive sustainable construction material regulations and regulations related to incentives that are more easily applied to road projects.

8. Research Limitation and Recommendation for Future Research

The limitation of this study comes from the limited research conducted in one country. This study was also conducted within ten stakeholder groups, which limited the respondent criteria. The limitation of this study is also in the form of qualitative research on stakeholders whose perceptions may change over time. Stakeholder perceptions can also change with political, social, and economic developments in a country.

In future research, key performance indicators can be developed to analyze and evaluate the level of implementation of strategies to increase stakeholder engagement in the implementation of sustainable lean construction. Further research needs to be conducted with more stakeholder groups that cover more roles in sustainable lean construction. In addition, it is necessary to conduct research on the communication management of stakeholder engagement strategies adopted from KAIZEN Continuous Improvement in construction projects.