Measuring the Sustainability of Construction Projects throughout Their Lifecycle : A Taiwan Lesson

Researchers have proposed many industrial or national sustainability evaluation indicator systems during the past decade, although there has not yet been a project-level sustainability evaluation system for the evaluation and execution monitoring of the sustainability status for a construction project. Without such an evaluation system, it will be difficult for the planners to plan the sustainable project objectives, for the contractors to select the sustainable execution alternatives, and for the facility managers to operate sustainable constructed facilities. To meet the abovementioned requirements, this paper presents an effort conducted in Taiwan to propose a Construction Project Sustainability Assessing System (CPSAS) considering three pillars of sustainability: environmental, social, and economic, based on the theoretical backgrounds from the literature and former successful sustainable projects. The proposed CPSAS comprises four levels: Level 1, 3 main pillars; Level 2, 8 categories; Level 3, 19 sub-categories; and Level 4, 31 indicators. Different selections of indicators for application in different project phases are suggested according to the prioritization via questionnaire surveys. A procedure for sustainable project management with the proposed CPSAS is suggested to the project management team. Finally, three green building projects and two civil infrastructure construction projects of Taiwan were tested to demonstrate the feasibility of the proposed CPSAS. It is concluded that the proposed CPSAS is useful for construction stakeholders to achieve sustainability more effectively during the execution of a construction project.


Introduction
The construction industry has been labelled a non-sustainable industry due to its high energy consumption and greenhouse gas (GHG) emissions, but low productivity.Statistics show that the building industry consumes 40% of energy and emits almost 40% of CO 2 in the USA and other developed countries [1,2], while wasting 57% (compared to 26% in other industries) of its resource inputs during the production process [3].Paradoxically, the poor performance offers the construction industry a unique opportunity to play the key role in reducing negative environmental impacts, thereby improving global sustainability [4].
Previous researchers have offered different approaches to improve the sustainability of the construction industry, including green innovation of construction methods [5][6][7], promotion of green building technologies [8,9], development of warm mix asphalt technology that reduces energy consumption and reduces the emission of greenhouse gases and other hazardous compounds [10][11][12], reuse waste materials (e.g., burning coal in power plants) to reduce environmental impacts [13,14], and implementation of techniques and initiatives for GHG emission elimination [15,16].As most of the above-mentioned efforts have focused on improvements derived from the technology or process levels, and affecting only single or multiple activities in a construction project, their improvements or impacts on the overall project were quite limited.On the other hand, some other researchers have established different industrial or national indicator systems to evaluate the sustainability of the construction sector of a country [17][18][19][20].Although such types of sustainability evaluation systems are more comprehensive in assessing the sustainability of the construction industry, they are, however, less useful for developing effective strategies to improve the sustainability of a construction project.
Considering the drawbacks of the above two categories, another category of approach that focuses on the project level has been proposed.Labuschagne and Brent [21,22] have proposed a staged project Life Cycle Management (LCM) framework for evaluating the environmental impacts of a new product during the innovation project lifecycle.Although it focuses only on the environmental impacts of a product, such an evaluation framework provides a promising alternative for sustainability monitoring and the improvement of a construction project.
Based on Labuschagne and Brent's concept, the current research proposes a comprehensive project-wise sustainability evaluation framework for a construction project; it provides the project engineers and managers with a useful tool for evaluating and monitoring the sustainability of construction activities throughout the project lifecycle so that effective strategies for sustainability improvement can be more efficiently identified and planned.
The remainder of the paper is organized as follows: the previous sustainability evaluation systems related to this research are reviewed first, then the methodology of current research is described in details; this is followed by presentation of the proposed CPSAS.The case studies of five real-world construction projects are demonstrated after presenting the proposed CPSAS; this is followed by the suggested procedure for management of sustainable construction projects.Finally, findings of the research are concluded and future directions after this research are recommended.

Review of Relevant Sustainability Evaluation Systems
The primary concept of sustainability was first proposed in early 1980s.The term sustainable development' was employed in the report to the United Nations General Assembly (UNGA) by the World Commission on Environment and Development (WCED) [23].The currently widely adopted three pillars (Economic, Social, and Environmental) of sustainability were promulgated in the early 1990s's [24].Such a three-pillar framework for the assessment of sustainability was adopted by most current national-level sustainability evaluation systems [17,18,20] discussed previously.In regard to improving the sustainability of construction engineering, especially from the viewpoint of project execution, the relevant works in the literature are reviewed below.
The concept of "sustainable construction" was found in literature of the First International Conference on Sustainable Construction in Tampa, Florida, US in 1994 [25].Hill and Bowen [25] proposed a detailed list of principles and conceptual framework for attaining sustainable construction in terms of four pillars: social, economic, biophysical (relevant to environmental) and technical perspectives.Fernández-Sánchez and Rodríguez-López [26] proposed a method to identify sustainability indicators for construction project management.In their report, a case application of the proposed method was simulated for the infrastructure projects in Spain, which resulted in a list of 30 macro-indicators for assessing the sustainability of an infrastructure project.The methodology proposed by Fernández-Sánchez and Rodríguez-López is quite general, so it can be applied to other types of construction projects.Two other similar works for the identification of sustainability indicators of construction projects, but using different approaches, were conducted by Shen et al. [27] and Huang and Hsu [20], respectively.Shen et al. [27] collected the feasibility study reports of 87 construction projects from China to identify 34 attributes (indicators) related to the sustainability of four types of construction projects.Huang and Hsu [20] identified 30 sustainability indicators of construction engineering from important research literature and government regulations.Most of the above works, except for the first one by Hill and Bowen [25], adopted the three-pillar perspective, i.e., environmental, social and economic sustainability of construction project.However, several important issues should be taken into account to develop an appropriate sustainability evaluation system for a construction project, as pointed out by different researchers: (1) a more comprehensive angle of sustainability, including product (i.e., the constructed structures in construction project), process (the management process), organization, key stakeholders (project manager and team members) [28], and economic concerns [29,30]; (2) the number of indicators should be not too many for practical and cost-effective implementation [26].Several researchers have suggested very similar numbers of indicators that are close to 30 [20,26,27], indicating that an indicator system with around 30 indicators is more practical and cost-effective for project implementation; (3) lifecycle concern: the indicator system should not only emphasize the construction project lifecycle (i.e., feasibility study, planning, procurement, construction, and turnover), but also the facility lifecycle (i.e., operation, maintenance, and demolition) [25,26,28]; and most importantly (4) project focus: the indicators should be relevant to the project operations and tasks for management effectiveness since the construction objectives need to be accomplished via project execution [28].
A general methodology was proposed by Fernández-Sánchez and Rodríguez-López [26] to identify the sustainability indicators in construction project management: (1) Review of documentation; (2) Compilation of information through surveys with project stakeholders; (3) Compilation of information through interviews with domain experts; (4) Brainstorming by the project participants; (5) Comparison with other areas and other existing tools; (6) Analysis by checklists related to similar previous projects; and (7) Using diagramming techniques to show the relationship between the system elements and their causality.The two most adopted approaches for developing such kinds of indicator systems are [28]: (1) documentation and literature review: identifying the candidate indicators by reviewing previous literature and legislation documents; and (2) expert survey: conducting questionnaire or interview surveys, or holding focus group meetings, to collect opinions from different stakeholders to determine which indicators should be included.The current research adopts both of these approaches by reviewing the literature to identify candidate indicators first, and then verifying and refining the candidate indicators by expert judgment, via focus groups, interviews and/or questionnaire surveys.

Development of Sustainability Evaluation System for Construction Projects
Based on a literature review [25][26][27][28], a research methodology for the current study was planned to identify the relevant sustainability indicators for the evaluation and monitoring of construction projects.

Research Methodology and Procedure
The research procedure adopted in the current research is depicted in Figure 1; it includes the following steps and methods: ( They need to be redefined to fit the requirement for application in a construction project.Finally, 57 candidate indicators belonging to 20 categories were identified as candidate sustainability indicators (SIs) for further analysis.(2) Pre-screening and prioritizing preliminary SIs for applicable lifecycle stages through domain expert interviews: semi-structured expert interviews were conducted with five domain experts (including a government officer from the River Management Bureau, an architect with a significant amount of green building design experience, a consultant engineer with ecological construction method design and supervision experience, a professional construction manager from one of the major consulting firm, and a site engineer of a general contractor for a green building project) to determine the applicable stages in a project lifecycle based on the four criteria mentioned previously in the literature review: (1) as comprehensive as possible: applicable to different project types and involving important stakeholders; (2) practical to implement: with an indicator number near 30; (3) lifecycle concern: covering all phases of the project lifecycle; and (4) project focus: should be relevant to project management processes or techniques.The interviews were conducted every week for nearly three months until a consensus was reached.The expert interviews finally concluded that 31 preliminary sustainability indicators out of the 57 initial candidate indicators may be applicable to the eight different project stages: (3) Testing with historical sustainable projects: a checklist analysis method adopted from Rodríguez-López [26] was conducted through 12 historical projects to test whether the required information for the selected 31 preliminary SIs could be acquired from real world projects.The historical sustainable construction projects were collected from two public sources: (1) eight green building cases from Taiwan Green Building Council [31]; (2) four ecological construction project cases from the Public Construction Council [32] (refer to Table 1 for the details of the 12 sustainable cases).
The testing results show that all 31 preliminary SIs identified by expert interviews in Step (2) were found to be applicable at least in four out of the 12 cases.The five preliminary SIs with the least applicable historical sustainable construction projects are: (1) E3c1 (Usage of Vertical Green Planting), 83.3% (10/12) applicable; (2) S1a1 (Improvement of Average Occupation Area), 33.3% (4/12) applicable; (3) S1a2 (Improvement of Infrastructure), 66.7% (8/12) applicable; (4) S1a3 (Certified Green Building), 83.3% (8/12) applicable; and (5) S1b1 (Prevention of Disaster), 41.7% (5/12) applicable.Although these five indicators are not applicable to all cases due to specific project characteristics, they are generally useful for sustainability assessment.As a result, all 31 preliminary SIs are considered applicable for the sustainability assessment of construction projects.
(4) Prioritization of selected preliminary SIs through a questionnaire survey: in order to assess the acceptance of the proposed CPSAS from the industry, a questionnaire survey was conducted with 45 experienced industrial practitioners (with previous participation in at least one sustainable construction project, including the owners, the consultants or designers, the general contractors, the suppliers and sub-contractors) of the published historical sustainable construction projects [31,32].The questionnaire was designed to assess their agreement with the SIs in the eight stages of a project lifecycle.The statistics on the questionnaire returns are summarized in Table 2. Finally 38 effective responses were received, the overall return rate for the questionnaire survey is 84%.The results of the questionnaire survey are shown in Table 3.The profile information of the respondents including their professional positions and seniority of practical experience is depicted in Figure 2. The inter-rater reliability scores [33] for each group of respondents are listed in the fifth column of Table 2 to show the reliability of the survey results.The percentage statistics of survey results for the questionnaire are provided as the supplementary materials of the paper.
(5) Case study demonstration: two types of construction projects (including three green building projects and two ecological civil infrastructure construction projects) were selected for testing with the established CPSAS to demonstrate its applicability.The applications of CPSAS in sustainable construction project management are also addressed and discussed with the case demonstrations.
(5) Case study demonstration: two types of construction projects (including three green building projects and two ecological civil infrastructure construction projects) were selected for testing with the established CPSAS to demonstrate its applicability.The applications of CPSAS in sustainable construction project management are also addressed and discussed with the case demonstrations.(5) Case study demonstration: two types of construction projects (including three green building projects and two ecological civil infrastructure construction projects) were selected for testing with the established CPSAS to demonstrate its applicability.The applications of CPSAS in sustainable construction project management are also addressed and discussed with the case demonstrations.

Proposed Construction Project Sustainability Assessing System (CPSAS)
The resulting SIs for assessing the sustainability of a construction project, namely the Construction Project Sustainability Assessing System (CPSAS), is illustrated in Figure 3.The framework of CPSAS comprises four levels: (1) Level-1: Sustainability Pillars (SP): 3 pillars of sustainability are defined: environmental sustainability (E), social sustainability (S), and economic sustainability (EC); (2) Level-2: Sustainability Categories (SC): total of 8 sustainability categories belonging to the 3 pillars are defined; (3) Level-3: Sustainability Sub-Categories (Sub-SC): total of 19 sustainability sub-categories are identified for the eight sustainability categories; (4) Level-4: Sustainability Indicators (SI): total of 31 sustainability indicators are identified.The detailed definitions for the 31 SIs are shown in Table 3.Based on the agreement percentage (%) depicted in Table 3, the SIs with different importance suggested to be adopted for different stages of the project lifecycle are shown in Table 4.
With the proposed CPSAS, the overall Project Sustainability Index (PSI) can be calculated for a specific construction project.According to CPSAS defined in Table 3 and Figure where PSI is the Project Sustainability Index in percentage (%); m is the number of qualitative (non-quantitative) indicators; PSI nq (i) is the evaluated result of the ith qualitative indicator; n is the number of quantitative indicators; PSI q (j) is the evaluated result of the jth qualitative indicator.The non-quantitative, PSI nq (i), and quantitative, PSI q (j), sustainability indicators in Equation ( 1) are further defined in the following: Non-quantitative Sustainability Indicators (PSI nq ) In CPSAS, there are 12 indicators of PSI nq .The results of the 12 PSI nq indicators are either 'Pass' (noted as 'Y' in Figure 3) or 'Fail' (noted as 'N' in Figure 3).When an indicator satisfies the defined requirements, it is assessed as 'Y' with the PSI nq value of '1 ; otherwise, it is assessed as 'N' with PSI nq value of '0 .For example, 'E1d2-Usage of Green Energy (UGE)' requires the use of any kind of renewable energy (e.g., solar, wind, or co-generation electricity) utilized in the project.If any is in place, it is assessed as 'Y' (PSI nq = 1).

Quantitative Sustainability Indicators (PSI q )
There are 19 quantitative indicators of PSI q in the proposed CPSAS.Among these, 6 are assessed in percentage (%) and 13 are assessed in numbers.Most of the percentage indicators are ratios of two parameters collected from the project; the numeric (No.) indicators are counted in integer numbers.Thresholds are defined for different PSI q indicators.For example, for 'EC1a1-Ratio of Local Employment (RLE)', the threshold value may be set as 20% to encourage the creation of jobs for the local community by the project contractor.If the RLE is ≥20%, it is assessed as 'Y' (PSI q = 1); otherwise, it is assessed as 'N' (PSI q = 0).Similarly, an example of the numeric indicators for 'S1a3-Certified Green Building (CGB)', the threshold value required by the local regulation for the EEWH Green Building Certification System [34] in Taiwan requires at least four quantified items to be certified as 'Green Building'.
Finally, the overall PSI of the project is calculated using Equation ( 1).The Level of Project Sustainability (LPS) in this research is determined arbitrarily using the following rules: (1) If PSI < 50%, the project is determined as 'Low-Sustainability; (2) If 50% ≤ PSI < 76%, the project is determined as 'Bronze Sustainability; (3) If 76% ≤ PSI < 86%, the project is determined as 'Silver Sustainability'; (4) If PSI ≥ 86%, the project is determined as 'Gold Sustainability'.
It is noted that the criteria of LPS provide project stakeholders an overall figure of the project sustainability.It can be altered and tuned more appropriately by the project manager or the project owner after several practical applications of the proposed CPSAS.

Determining Indicator Criteria
The criteria of the Sustainability Indicators (SIs) in Table 3 will affect the overall Project Sustainability Index (PSI) and further determine the Level of Project Sustainability (LPS).As a result, it is very important to select appropriate 'Pass' or 'Fail' criterion for each SI.As discussed previously, some criteria are 'hard' requirements regulated by the local sustainability related regulations, e.g., the 'S1a3-Certified Green Building (CGB)' is regulated by the EEWH Green Building Code of Taiwan [34], the 'E2e2-Usage of Green Labeled Product (GLP)' is regulated by the Public Construction Commission (PCC) of Taiwan [32].The other criteria are 'soft' requirements that can be determined by the project stakeholders according to their expectations or intentions to achieve the project sustainability.For example, the 'E3a1-Ratio of Planting Area (RPA)' of environmental pillar will improve the biodiversity and living quality in the long term; the 'EC1a1-Ratio of Local Employment (RLE)' of economic pillar will create jobs for local community and will improve social relationship between the facility owner and the local residents in the long term.The criteria of both abovementioned indicators can be set up by the project owner for their long term goals.

Demonstrated Case Studies
In this section, five construction projects, including three green building projects and two civil infrastructure construction projects, were selected for testing the proposed CPSAS to demonstrate its applicability.

Background of Selected Case Projects
The background information on the five selected real world cases are described in Table 5.The sustainability assessments were tested for different project stages according to the information available for each project during the time the research was conducted.Two (Case I and II) projects were assessed for the Plan and Design (P&D) stage; one (Case III) project was assessed for Construction (C) stage; one (Case IV) project was assessed for Turnover (TO) stage; and one (Case V) project was assessed for Operation (O) stage.

Assessment of Sustainability Indicators
The Sustainability Indicators (SIs) of the proposed CPSAS were assessed according to the definitions of the SIs in Table 3.The first step in assessing the SIs was to determine the criterion of 'Pass' for each indicator in the CPSAS.In the case study, the criteria were mainly determined according to the local regulations.For example, the Public Construction Commission (PCC) of Taiwan requires 'E2e2-Usage of Green Labeled Product (GLP)' to be at least 10% for a sustainable public construction project; thus, the criterion of 'Pass' criterion of E2e2 was '≥10%'.Similarly, the certified green building according EEWH standard requires at least four qualified items, so the 'Pass' criterion for 'S1a3-Certified Green Building (CGB)' was set as '≥4'.The other criteria for the rest indicators are shown in the fifth column of Table 6.The results of the assessment for the SIs of the six demonstrated cases are depicted in Column 6-10 of Table 6.The original values for the numeric indicators (PSI q ) are represented in the parentheses, and the assessed results are shown in front of the parentheses.There are some assessed indicators shown as 'N/A', which means the indicators are not applicable for the case due to the project characteristics.For example, the 'S1a1-Improvement of Average Occupation Area (AOA)' and 'S1a3-Certified Green Building (CGB)' are not applicable for the river renovation project type of Case IV and the highway project type of Case V. Similarly, the 'S2a1-Measure of Conserving Cultural Monument (CCM)' and the 'S4a2-Fair Sharing of Benefits (FSB)' are not applicable for the river renovation project type of Case IV.All applicable indicators were assessed and given resultant values in Table 6.

Project Sustainability Index (PSI) Calculation
The PSI for each demonstrated case was calculated according to Equation (1).The calculation results are summarized in Table 7.It is noted from Table 7 that the overall project PSIs range from 71% to 92%.Case I is ranked as 'Bronze' level; Cases III and IV are ranked as 'Silver' level; and Cases II and V are both ranked 'Gold' level for their sustainability.The proposed CPSAS not only provides an overall PSI, as shown in Table 6, but also provides the direction for improving the sustainability for project management.For example, Case I is assessed as the least sustainable project among the five demonstrated cases.From Table 5, it is noted that many SIs are poor in sustainability performance, e.g., 'E2a2-Usage of Low Air Pollution Method (LAP)', 'E2d1-Measure of Noise Reduction (MNR)', 'E3a1-Ratio of Planting Area (RPA)', 'E3c1-Usage of Vertical Green Planting (VGP)', and 'S4a2-Fair Sharing of Benefits (FSB)'.Most of these indicators can be improved during the 'Plan & Design' stage (when the assessment takes place).Thus, the project team is guided to plan the actions for sustainability improvement.
Nevertheless, the proposed CPSAS provides the project management team with a suggested list of assessment indicators for monitoring the project sustainability during each stage of a project lifecycle.Such project management initiatives can be triggered by a 'Stage-gate' procedure, as suggested in Figure 4.In the procedure of Figure 4, the 'Stage-gate' is set at the end of each project stage, where the PSI for the stage is assessed by the project management team.If the PSI is not satisfied, improvement actions should be planned and implemented according to the SI assessment results obtained from CPSAS; otherwise, the project is allowed to proceed to the next stage.Finally, the project sustainability performance report can be generated as a lesson learned for future projects at the end of the project.In the procedure of Figure 4, the 'Stage-gate' is set at the end of each project stage, where the PSI for the stage is assessed by the project management team.If the PSI is not satisfied, improvement actions should be planned and implemented according to the SI assessment results obtained from CPSAS; otherwise, the project is allowed to proceed to the next stage.Finally, the project sustainability performance report can be generated as a lesson learned for future projects at the end of the project.

Conclusions and Recommendation
The construction industry has been criticized as a non-sustainable industry due to its low productivity but high resource consumption.However, there has not yet been an effective tool to monitor and achieve the expected sustainability for construction projects from stakeholders' viewpoints.In this paper, a Construction Project Sustainability Assessing System (namely CPSAS) is proposed to provide the engineers and the manager with a tool to monitor and control the process sustainability of a construction project.The proposed CPSAS comprises four levels: Level 1, 3 main pillars; Level 2, 8 categories; Level 3, 19 sub-categories; and Level 4, 31 indicators.Five demonstrated cases, including three building projects and two civil construction projects, were selected to test the feasibility of the proposed CPSAS.A procedure for sustainable project management with the proposed CPSAS is also suggested to the project management team.
Although the study was conducted through surveys based on the literature, historical sustainable construction projects and the domain experts in Taiwan, the proposed model can be tailored to fit the need of sustainability in the other countries or areas.Table 4 offers the project management team the selection set of sustainability indicators to meet requirements of different project phases.Table 6 provides the project stakeholders with a tool to set up thresholds of sustainability indicators that determine the levels of sustainability expected by different project participants.Finally, Figure 4 is offered as a guide for the implementation of sustainable construction project management.The project stakeholders (especially, the project owners and managers) have to determine the thresholds for the 'Pass or Fail' criteria according to their expectations and requirements on project sustainability.Moreover, the Level of Project Sustainability (LPS), which provides a compass to monitor the overall project sustainability should be adjusted with more experiences collected from practical implementations.With such a tool, the project management team is better equipped to achieve a more sustainable construction project.It is concluded that the proposed CPSAS is useful for construction stakeholders to effectively monitor the sustainability of the construction activities during the project lifecycle so that the project team is able to plan strategies to manage the project in order to achieve effective construction sustainability.
The proposed CPSAS has been tested with five sustainable projects; however, more and different types of sustainable projects need to be considered for comprehensive verification.The research team plans to implement the proposed CPSAS in a land development project located in Hsinchu City in North Taiwan.Other specialized construction projects also need to be tested, such as industrial construction projects, ocean construction projects, etc.

Author Contributions:
The conceptualization of the research, the initial research methodology, and funding collection were originated by Wen-der Yu.Shao-tsai Cheng further planned detailed research methodology (including the questionnaire design).Wei-cheng Ho and Yu-hao Chang, who were graduate students of Yu and Cheng, implemented the research methodology and conducted questionnaire survey.Ho and Chang were also in charge of data collection and the initial analysis of survey results.The statistical analysis and validation was conducted by Cheng.The paper was mainly written and organized by Yu, who was also in charge of the administration of the research project.

Figure 2 .
Figure 2. Profile information for the respondents of questionnaire survey.

Figure 2 .
Figure 2. Profile information for the respondents of questionnaire survey.Figure 2. Profile information for the respondents of questionnaire survey.

Figure 2 .
Figure 2. Profile information for the respondents of questionnaire survey.Figure 2. Profile information for the respondents of questionnaire survey.
3, there are two types of indicators: (1) Quantitative indicators: measured by the percentage (%) of values or quantities (No.) of the indicators; and (2) Non-quantitative indicators: measured by 'Yes or No (Y/N)' of the outcome of the indicators.The two indicator types are aggregated in PSI using the following equation:
Sustainability 2018, 10, x FOR PEER REVIEW 13 of 17 lifecycle.Such project management initiatives can be triggered by a 'Stage-gate' procedure, as suggested in Figure 4.

Figure 4 .
Figure 4. Suggested management procedure for attaining sustainable project with the proposed CPSAS.

Figure 4 .
Figure 4. Suggested management procedure for attaining sustainable project with the proposed CPSAS.

Table 1 .
Information on 12 tested sustainable construction projects.
Note: * EEWH is the Green Building Certification System of Taiwan[31].

Table 2 .
Statistics on the questionnaire distribution and collection.

Table 3 .
Results of questionnaire survey for the applicability of sustainability indicators in the project lifecycle.

Table 4 .
Suggested SIs for different stages of project lifecycle.

Table 5 .
Suggested SIs for different stages of project lifecycle.

Table 6 .
Results of SI assessment for the five demonstrated cases.

Table 7 .
Overall Project Sustainability Index (PSI) for demonstrated case projects.