Developing green bridge rating system using Simos’ procedure

Peer review under responsibility of Housing and Building National Research Center.

Abstract

Sustainable development principles have been implemented in various sectors including construction. Proper development and operation of infrastructure projects, such as bridges and highways, can contribute significantly to the mission of sustainable development. In this respect, there is little existing work on appropriate methods to assess the sustainability performance of bridge projects. This paper introduces a key-list of gathered important criteria that affect the sustainability of bridge projects. Various construction industry standards have been reviewed in order to decide the criteria that influence sustainability of bridge projects. The initial list of criteria has been identified by unstructured interviews. Then, structured interviews and questionnaire survey have been conducted to identify the final list that is deemed important in rating green bridges. Various construction industry standards have been reviewed to decide on the criteria that influence sustainability of bridge projects. Final criteria results from this paper are used to develop a green bridge rating system to achieve sustainable development. Degree of importance and weights of these criteria are determined using Simos’ procedure. Five classes of bridges are proposed to judge their status with respect to sustainability, with these being Non-Green, Certified, Green, total Green, and Evergreen.

Keywords:

• Sustainability
• Green bridges
• Rating systems
• Simos’ procedure

Introduction

Various construction standards have been developed to examine the highway bridge projects’ sustainability from different perspectives. These standards include Environmental Protection Agency (EPA) [1], American Association of State Highway and Transportation Officials (AASHTO) [2], Federal Highway Administration (FHWA) [3], and Leadership in energy and environmental design (LEED) [4]. World Commission on Environment and Development (WCED) [5] defined sustainability development as “meeting the needs of the present without compromising the ability of future generations to meet their own needs”. No doubt that bridge projects have been given particular importance as they have a great impact on the economy, social aspects and the environment. The proper development and operation of bridge construction projects can contribute significantly to the mission of sustainable development. Bridge construction projects include a wide range of construction works such as highway bridges, railway bridges, and others. Bridge constructions play an essential role in economic and social developments. It is estimated that a one percent increase in infrastructure stock is associated with a one percent increase in Gross Domestic Product GDP [6]. Easterly and Rebelo [7] reported that investment in highway bridges and communication has a positive effect on the economic growth. Combustion of fossil fuels leads to greenhouse gas emissions. Overuse of water for irrigation (which accounts for about 90% of water withdrawal in most low-income countries) damages soil and severely restricts water availability for both industry and households [8]. Some infrastructure investments, especially bridge construction, can put unspoiled natural resources at risk and threaten indigenous communities. Therefore, in line with the promotion of sustainable development worldwide [8-9], it is of utmost importance to find ways for gaining better sustainability performance while executing bridges which will remain extensive in the near future. While LEED is the building industry benchmark in sustainability, there are other rating systems implemented and in various stages of development. The Green Guide for Healthcare [10] was created in 2003 for hospitals and is currently in the process of being incorporated into LEED [4]. Green roads [11] is a rating system focusing on sustainable transportation practices. Examples for different standards are GreenLites [12] (Leadership in Transportation and Environmental Sustainability), and Stantec’s Green Guide [13]. A positive impact of green bridge projects is that the productivity of workers increases. In addition, green bridge projects make working environment more attractive, comfortable, and provide healthier conditions for its constructors and users. This is done by achieving the aspects of sustainability criteria. Since working conditions are improved, workers are healthier and therefore use less sick days. This can result in large financial benefits for the employer [14]. Bridges with lower life cycle costs will tend to have lower environmental impacts. In other words, the least expensive bridge alternative is also likely to have the least associated emissions and embodied energy. The key is to consider the total costs for design, construction, use, maintenance, demolition, and salvage, not merely initial construction cost. Many recycled materials, including steel, pozzolan cements, wearing surface aggregates, and construction waste, are cost competitive in terms of both initial cost and life cycle cost with virgin alternatives. There is no significant difference in average construction costs for green buildings as compared to non-green buildings [15]. Similar conclusion was drawn when investigating the costs associated with the thirty-three LEED certified municipal buildings built by the state of California [14]. The Federal GSA decided to fund its green building mandate by allocating a 2.5% construction budget increase. Whichever estimate is used, the sources agree that the initial investment in green building is rewarded by many times over the life of the structures. This is due to lower life cycle costs in the form of decreased energy, water, and waste use [14]. This indicates that the proposed green bridge standard does not increase construction costs and will certainly reduce life cycle costs and maintenance costs. This paper proposes a methodology for developing a rating system for green bridges. The research is developed considering the following procedure: (1) creating an initial list that contains the most important criteria to build up green bridge rating system, (2) developing the final list of criteria using statistical analysis descriptive tests according to the degree of importance of each criterion, and (3) using Simos’ approach to determine the weights of each criterion.

Research methodology

In an effort to develop a rating system for green bridges, a three-phase research methodology has been followed and described hereinafter.

▪	Literature Review Phase: This phase was started prior to the commencement of the questionnaire survey. It was devoted for reviewing the literature for identifying the criteria affecting bridge sustainability.

▪

Unstructured Interviews Phase: In order to corroborate the findings and views of the earlier studies, several unstructured interviews were individually conducted with nine experts in bridge construction projects. The participating experts were requested to identify and enumerate the criteria affecting green bridges from their own point of view in a separate list. During these interviews, the participating experts were only asked general questions regarding the affecting criteria. In all cases, notes were taken without any influence or intervention. Next, a combined list was prepared from the participant’s answers.

▪

Questionnaire Survey Phase: Questionnaire survey was used to finalize the list of criteria essential for constructing green bridge rating system for bridge projects. It consists of three main sections; Section one includes the respondent personal data, while section two is the principal component of the questionnaire. The list of criteria associated versus levels of importance is included. Section three has a list for any extra information that can be added by the expert. The methodology of eliciting expert response regarding his/her assessment of the degree of importance associated with each criterion is performed based on a scale that ranges from “1” to “10” which corresponds to “Very Low Importance” to “Very High Importance”.

Identification of criteria

Several literature efforts have been reviewed to identify the list of criteria that can be considered in the rating system of green bridges [4,15^[16][17]18]. Subsequently, several structured and un-structured interviews with experts in bridge construction have been conducted. The initial list contains twenty-seven criteria that belong to five categories: Project Requirements, Environment and Water Category, Access and Equity Category, Construction Activities Category, Materials and Resources Category. This is listed in Table 1.

Table 1 Initial criteria list.

ID	Criteria	Description
Project requirements category
PR-1	Life Cycle Cost Analysis	Presenting a Life Cycle Cost (LCC) analysis of all significant bridge materials to be used in the Project.
PR-2	Cultural Heritage	Incorporating architectural, construction and technical solutions which excel in reflecting national and regional cultural heritage, while contributing to the environmental performance of the bridge.
PR-3	Noise Mitigation Plan	Strategies toward noise mitigation, as construction of noise barriers, tinning of pavement to reduce noise levels.
PR-4	Waste Management Plan	Presenting a project Waste Management Plan that includes strategies from reducing, and, where possible, re-using and recycling the waste arising from the project operations.
PR-5	Pavement Management plan	Strategies toward extended green pavement construction, life; design and rehabilitation.
PR-6	Site Maintenance Plan	Providing simple and easily-followed Operations manual bridge components.
PR-7	Potential for Innovations	Presentation of an innovative design or construction practices which have a significant measurable environmental benefit and implementation plan, and bridge reuse.
PR-8	On-site Renewable Energy	Percentage of total energy demand is supplied through renewable energy, utilizing on-site or off-site sources. An on-site and/or off-site renewable energy feasibility study has been undertaken.
PR-9	LEED Accredited Professional	At least ONE principal participant of the project team shall be a LEED Accredited Professional (AP).
Environment and water category
EW-1	Site Vegetation	Consider the use of native vegetation with no irrigation
EW-2	Habitat Restoration	Demonstrating a suitable strategy for conserving or restoring natural areas to provide habitat and promote biodiversity, including the preserving/replanting of trees found on site.
EW-3	Sustainable sites Selection	Projects that redevelop a brown field site in order to achieve maximum benefit from such areas and to rationalize land use. The site has been including an Environmental Site Assessment),
EW-4	Respect for historic sites	Demonstrating a suitable strategy for conserving and protecting remains of historic or cultural interest that is part of or nearby the site.
Access and equity category
AE-1	Intelligent Transportation Systems	Demonstrating strategies to reduce reliance on traditional transportation systems, and encourage the use of greener and intelligent methods of transport.
AE-2	Providing a Bridge User Guide	Building user guide containing the necessary technical and non-technical information for the bridge users/occupant to enable the efficient and responsible operation.
AE-3	Periodic Maintenance Schedule	The provision of a Periodic Maintenance Schedule, which should be comprehensive and regularly updated.
AE-4	Pedestrian/Bicycle Access	Consider approaches for improving conditions for bicycle and pedestrian travel within roadway improvement projects. Conditions within project corridors provide sufficient comfort and safety level in order to encourage pedestrian and bicycle movements, thereby reducing the need for driving (and accompanying energy usage) for many short distance trips.
AE-5	Transit Access	Increased use of rail transit can reduce traffic on highway bridges in the most congested areas, potentially reducing congestion, and fuel consumption. Park-and-Ride lots serve as an intermodal staging locations.
AE-6	Visual Enhancements	The project provides the traveling public an opportunity to see a scenic view either during travel or by providing a stopped observation point.
Construction activities category
CA-1	Equipment Emission Reduction	Mitigating noise and exhaust emissions from machinery and equipment on Site.
CA-2	Access Roads	Providing proper access roads for trucks to reduce any negative impact on the environment during site operations.
CA-3	Storage/Separation areas	Providing site storage areas, separation of flammable and toxic materials and prevention of soil pollution in these areas.
Materials and resources category
MR-1	Pavement Reuse	Building cost effective pavement systems by using recycle and/or reuse materials.
MR-2	Earthwork Balance	Balancing cuts and fills can reduce the need for borrow excavation, which can reduce vehicle emissions and pollution generated by the transportation of soils in and out of the project corridor
MR-3	Recycled Materials Reuse	Preserving natural resources and protecting the environment by reducing the use of natural resources and increasing the use of recycle/reuse materials
MR-4	Regional Materials	Projects with specifications that support the use of local materials depending on the location of the project, whenever practical.
MR-5	Long-Life Pavement	Specifying the use of perpetual HMA pavement with 40 or more years of design life.

Questionnaire survey

The questionnaire survey contains twenty-seven criteria that have been collected from the literature and reviewed by nine experts via un-structured interviews. Experts have responded to the survey to satisfy the number of the designed sample size to select the most important criteria. Samples of construction, consultants and employer representative companies have been approached in order to get their opinions on the questionnaire feedback.

Sample size

The questionnaire sample was designed on the basis of the engineers’ classification of the Egyptian Engineering Syndicate. It was distributed only to the designers, owner’s representative and various types of consultants which are registered in the Engineering Egyptian Syndicate. It is assumed that the experience of construction mainly with bridge design and construction exist in this class of engineers. Approximately, 5000 engineers are registered as bridge consultants.

The required sample size can be statistically calculated according to Eq. (1) as follows [19]:(1) $n=\frac{{(Z\alpha /2)}^2\ast P\ast (1-P)}{d^2}$(1) where n is the sample size, Zα/2 is the critical value from statistical tables, P is the percentage of sample population to the total population, and d is the accepted error percentage.

For a sample population of 5000 and a total population of 116,000 (registered civil engineers in the Egyptian Engineering Syndicate), the accepted error percentage in the questionnaire is 10%; Zα/2 = 1.645 and the minimum sample size is estimated to be 11.1. In order to enhance the accuracy of the questionnaire survey, it was decided to increase the sample size of the experts to be thirty experts classified as consultant engineers, construction supervision engineers, and owner representative engineers. According to the questionnaire feedback, there were 21, 8, and 1, respondents for the consultant engineers, construction supervision engineers, and owner representative engineers, respectively. All experts had more than 10 years in bridge design and construction supervision experience.

Questionnaire results

Based on the survey, criteria that were found to be weak or of no influence were eliminated from a list according to the statistical analysis. Criteria of mean average value less than or equal to five were eliminated from the list. Twenty-one criteria have been selected and considered by the experts as a result of the questionnaire. It should be noted that six criteria have been excluded from the twenty-seven-criterion list forming a more reliable list of twenty-one criteria as estimated in Table 2. The eliminated criteria are Cultural Heritage (PR-2), Pavement Management plan (PR-5), LEED Accredited Professional (PR-9), Site Vegetation (EW-1), Periodic Maintenance Schedule (AE-3), and Access Roads (CA-2). Project Requirements category has three eliminated criteria which is the highest number of eliminated criteria in a category, whereas, Environment and Water category, Access and Equity Category, Construction Activities Category have one eliminated criterion. Materials and Resources Category has no eliminated criterion. After having the importance of the gathered criteria and eliminating the low important Criteria, the relative importance for the remaining criteria is obtained. Relative importance could not have been acquired in an earlier stage since it would have been a complex action to get the importance of criteria.

Table 2 Questionnaire survey results.

ID	Criteria	Mean	Standard error
PR-1	Lifecycle Cost Analysis	7.5	0.156
PR-2	Cultural Heritage	5.0	0.152
PR-3	Noise Mitigation Plan	6.1	0.125
PR-4	Waste Management Plan	6.4	0.185
PR-5	Pavement Management plan	2.8	0.126
PR-6	Site Maintenance Plan	7.2	0.154
PR-7	Potential for Innovations	6.2	0.177
PR-8	On-site Renewable Energy	6.11	0.194
PR-9	LEED Accredited Professional	4.90	0.164
EW-1	Site Vegetation	4.81	0.153
EW-2	Habitat Restoration	6.21	0.144
EW-3	Sustainable sites Selection	6.90	0.156
EW-4	Respect for historic sites	8.18	0.111
AE-1	Intelligent Transportation Systems	6.80	0.144
AE-2	Providing a Bridge User Guide	6.26	0.149
AE-3	Periodic Maintenance Schedule	2.96	0.131
AE-4	Pedestrian/Bicycle Access	7.03	0.168
AE-5	Transit Access	6.96	0.170
AE-6	Visual Enhancements	6.19	0.145
CA-1	Equipment Emission Reduction	6.56	0.167
CA-2	Access Roads	1.37	0.059
CA-3	Storage/Separation areas	7.70	0.126
MR-1	Pavement Reuse	6.81	0.182
MR-2	Earthwork Balance	7.07	0.175
MR-3	Recycled Materials Reuse	6.96	0.187
MR-4	Regional Materials	7.74	0.132
MR-5	Long-Life Pavement	7.41	0.129

As per Table 2, within Project Requirements Category, Life Cycle Cost Analysis (PR-1) is the most important criterion, whereas, the least important one is Pavement Management plan (PR-5). With reference to the second category Environment and Water Category, (Respect for historic sites (EW-4) is the most important criterion, whereas, the least important one is Site Vegetation (EW-1). With reference to the third category Access and Equity Category, Pedestrian/ Bicycle Access (AE-4) is the most important criterion, whereas, the least important one is Periodic Maintenance Schedule (AE-3). With reference to the forth category Construction Activities Category, Storage/Separation areas (CA-3) is the most important criterion, whereas, the least important one is Access Roads (CA-2) .With reference to the fifth category Materials and Resources Category, Regional Materials (MR-4) the most important criterion, whereas, the least important one is Pavement Reuse (MR-1). Fig. 1 illustrates the estimated mean values for the final list of criteria. The mean values of level of importance for the final list of criteria range from 6.11 to 8.19.

Fig. 1 Estimated mean values of importance level for the final list of criteria.

Estimating criteria weights

The relative importance is essential for assigning the weight of each factor. Weight allocation of criteria is consequently essential since it will be integrated with a ranking technique. Involved criteria are more or less important to make a decision, and most often they are conflicting or interacting in some way, so that it is not obvious how to combine them for reaching a final overall opinion. There are several possible aggregation procedures. Simos’ procedure [20^[21]22] has been chosen as an adequate aggregation procedure for the problem at hand. Simos proposed a technique that allows any decision maker to think about and express the way in which s/he wishes to hierarchize the different criteria in a given context. This procedure also aims to communicate to the analyst the information s/he needs in order to attribute a numerical value to the weights of each criterion. The procedure has been applied to different real-life contexts; it proved to be very well accepted by decision makers. Procedure has been followed to acquire both the relative importance and the weights of criteria.

Description of Simos’ procedure

The main concept of this approach is made up of correlating a “playing card” with each criterion. The action that the person is making has to manage the cards in order to rank them, inserting the white ones, allowing a rather intuitive understanding of the aim of this procedure [21]. The number of white cards (n) represents the number of criteria. There are a number of white cards that depends on the user’s needs. The next step is to ask the user to arrange these cards (criteria) from the least important to the most important. Therefore, the user arranged in ascending order according to the importance of the criteria. The first criterion in the ranking is the least important and the last criterion in the ranking is the most important. According to the user’s point of view, if criteria have the same importance (the same weight), it must build a subset of cards to hold them together with a clip or rubber band. As a result, the full pre-order on the entire (n) standards is obtained. Then, the user is asked to think about the fact that the importance of two successive criteria in the standings can be more or less close. During detection of the weights one must take into consideration which difference is larger or smaller in the importance of consecutive standards. Then, let him/her to make the white cards between two consecutive cards. The greater the difference between the weights of the criteria mentioned the greater is the number of white cards. Any white card means that the standard is not the same weight and the difference between the weights can be selected as a unit to calculate the interval between the weights.

Rating criteria weights

After acquiring the final list of important criteria, the first step is to acquire the normalized weights of each criterion as listed in Table 3, in order to get the global weights for each criterion. The mean values of the questionnaire survey have been used to represent the model rank. Then, the position of each criterion is estimated by the fact that the importance of two successive criteria in the standings can be more or less close. The highest normalized weight within categories are; Life Cycle Cost Analysis criterion (PR-1), Sustainable sites Selection (EW-3); Intelligent Transportation Systems (AE-1), Storage/Separation areas (CA-3), and Regional Materials (MR-4), respectively. The second step is to acquire the normalized weights among each category as presented in Table 4. Finally, the global weights of criteria are obtained by multiplying criteria’s local weights by their respective category weight as listed in Table 5.

Table 3 Relative weights of criteria within categories.

Criteria	Model Rank	Position	Global Weight
PR-1	73	74	0.185
PR-3	62	62	0.156
PR-4	64	65	0.162
PR-6	72	73	0.182
PR-7	62	63	0.155
PR-8	63	64	0.159
EW-2	62	62	0.289
EW-3	70	70	0.327
EW-4	82	82	0.383
AE-1	70	72	0.211
AE-2	63	63	0.186
AE-4	70	71	0.211
AE-5	70	70	0.211
AE-6	61	61	0.181
CA-1	66	66	0.462
CA-3	77	77	0.538
MR-1	67	67	0.188
MR-2	70	70	0.196
MR-3	68	68	0.190
MR-4	77	77	0.215
MR-5	75	75	0.210

Table 4 Relative weights of categories.

Category	Weight
Project Requirements	0.189
Environment and Water	0.205
Access and Equity	0.192
Construction Activities	0.209
Materials and Resources	0.206

Table 5 Simos’ estimated weights of criteria.

ID	Criteria	Weight
PR-1	Lifecycle Cost Analysis	0.0348
PR-3	Noise Mitigation Plan	0.0294
PR-4	Waste Management Plan	0.0306
PR-5	Pavement Management plan	0.0343
PR-6	Site Maintenance Plan	0.0294
PR-7	Potential for Innovations	0.0301
PR-8	On-site Renewable Energy	0.0348
EW-2	Habitat Restoration	0.0592
EW-3	Sustainable sites Selection	0.0669
EW-4	Respect for historic sites	0.0783
AE-1	Intelligent Transportation Systems	0.0403
AE-2	Providing a Bridge User Guide	0.0358
AE-4	Pedestrian/Bicycle Access	0.0403
AE-5	Transit Access	0.0403
AE-6	Visual Enhancements	0.0346
CA-1	Equipment Emission Reduction	0.0964
CA-3	Storage/Separation areas	0.1120
MR-1	Pavement Reuse	0.0386
MR-2	Earthwork Balance	0.0403
MR-3	Recycled Materials Reuse	0.0392
MR-4	Regional Materials	0.0444
MR-5	Long-Life Pavement	0.0432

Green bridge rating system

After obtaining the global weights using Simos’ procedure, a rating system for green bridges is proposed considering the credits that are listed in Table 6. The total credit values for the five categories are 26 for Project Requirements, 21 for Environment and Water, 23 for Access and Equity, 7 for Construction Activities, and 23 for Materials and Resources. Fig. 2 depicts the percent distribution of credits among the different categories. Five classes of bridges are proposed to judge their status with respect to sustainability. These classes are Non-Green, Certified, Green, Total Green, and Evergreen (see Fig. 3).

Fig. 2 Credit distribution among bridge rating system categories.

Fig. 3 Proposed bridge rating system classes.

Table 6 Proposed credits for green bridge rating system.

Criteria	Proposed credit
Project Requirements (26 Credits)
Lifecycle Cost Analysis	4
Noise Mitigation Plan	3
Waste Management Plan	4
Pavement Management plan	4
Site Maintenance Plan	3
Potential for Innovations	4
On-site Renewable Energy	4
Environment and Water (21 Credits)
Habitat Restoration	6
Sustainable sites Selection	7
Respect for historic sites	8
Access and Equity (23 Credits)
Intelligent Transportation Systems	5
Providing a Bridge User Guide	4
Pedestrian/Bicycle Access	5
Transit Access	5
Visual Enhancements	4
Construction Activities (6 Credits)
Equipment Emission Reduction	3
Storage/Separation areas	4
Materials and Resources (20 Credits)
Pavement Reuse	4
Earthwork Balance	5
Recycled Materials Reuse	4
Regional Materials	5
Long-Life Pavement	5
Total	100

Conclusion

This paper presented a procedure for green bridge rating system. A key-list of gathered criteria was retrieved from the literature and discussed with bridge experts via un-structured interviews. A questionnaire survey was prepared to elite the important criteria that affect the sustainability of bridge projects. The mean values of the criteria were estimated. Criteria that were found to be weak or of no influence were eliminated from a list according to the statistical analysis. Criteria of mean average value less than or equal to five were eliminated from the list. Twenty-one criteria have been selected and considered by the experts as a result of the questionnaire. Simos’ procedure was followed to acquire weights of criteria. Finally, a rating system for green bridges that consists of five classes was introduced to judge their status with respect to sustainability.

Conflicts of interest

We confirm there is no potential conflict of interest including any financial, personal or other relationships with other people or organizations within three years of beginning the submitted work that could inappropriately influence, or be perceived to influence.

Notes

Peer review under responsibility of Housing and Building National Research Center.