A critical review of roadway sustainable rating systems

Highlights

• Seven sustainable roadway rating systems were critically reviewed.

• Roads can be assessed with infrastructure, roadway or pavement rating systems.

• Rating systems mainly focus on resource and energy use.

• Third-party rating systems adhere more to the three-pillars of sustainability.

• Rating systems could greatly assist in social sustainability quantification.

Abstract

Multiple rating systems have been established to enhance the sustainable design and management of roadway projects. These systems are based on current best practices and demonstrate significant potential for assisting project managers in achieving environmentally sustainable and socially resilient smart transportation assets. HFowever, as it stands there is a significant lack of understanding on these systems, and thus lack of confidence in their implementation. Thus, this study aims to develop an up-to-date critical review on the most prominent rating systems currently in the global market. Specifically, the CEEQUAL, Envision, BE²ST-in-Highways, Greenroads, GreenLITES, Invest and GreenPave systems were selected and analysed in terms of their scopes, structures, common criteria, three-pillar adherence, and asset management effectiveness. The results of this study found: 1) system characteristics can be categorised by system scope (infrastructure, roadway or pavement) and assessment type (self-assessment or third-party, 2) third-party systems assessed the three-pillars of sustainability and the identified macro-categories more homogeneously, and 3) rating systems show strong potential for the social assessment of projects, but their consideration of life-cycle assessment could be more outcome-orientated. Future work should apply the rating systems to project case studies to further identify implementation, contextual and indicator pluralism issues.

Introduction

Roads are considered an essential part of modern daily life, and will have a key role in the development of smart cities too. The concept of the smart city consists of various characteristics, of which infrastructure sustainability can be considered one of them (Mohanty, Choppali, & Kougianos, 2016). In this context, the sustainable infrastructure characteristic would need to adhere to the triple bottom line, or the three pillars of sustainability (Silva, Khan, & Han, 2018), as originally defined by (Elkington, 1997). In response to this need, coupled with the current large energy (around 26 % of Europe’s total energy consumption (Eurostat, 2016)) and raw material use associated to roads, plus the need global need for US$90 trillion to be invested in new infrastructure over the next 15 years (UN, 2016), sustainable rating systems (SRS) for roads have grown in popularity.

These rating systems are composed of the current best-practices for road design, construction and maintenance and are recommended as one of the best-value procurement practices for sustainable highways for contractors and vendors (Muench, Migliaccio, Kaminsky, & Ashtiani, 2019). These system are therefore expected to assist in maximizing economic efficiency, improve social welfare, and help meet global sustainability targets (UN, 2019a; WHO, 2017). Where various case studies have supported their implementation. Such as, (Lew, Anderson, & Muench, 2016) who assessed 28 Greenroads projects and found a quantifiable improvement in performance compared to typical projects. And, in the experience of the Illinois Tollway, USA, a total of 22 projects pre- and post-Invest SRS were measured over 14 years, and found an increase in project sustainability over time (Illinois Tollway, 2015).

However, despite the fact that many sustainable choices outlined in these systems can measurably improve project sustainability with minimal or no impacts on cost (Anderson & Muench, 2013), there is still a limited amount of existing literature clarifying and explaining the differences between these systems (Simpson, Ozbek, Clevenger, & Atadero, 2014). Especially when a rating system, when used in the proper context, can provide a flexible approach to measure, manage, improve, and communicate sustainability at the project level (Muench, Scarsella, Bradway, & Hormann, 2012). Key areas of uncertainty in past literature can be condensed to the need of clarification towards: (1) indicator weighting, (2) triple-bottom line adherence, and (3) whole life-cycle considerations. Where, (Clevenger, Ozbek, & Simpson, 2013) and (Simpson et al., 2014) found that while systems tend to share similar ideas with regards to what sustainability aspects to focus on, especially resources and energy use, they largely differ in their approach to defining the importance of these aspects in a rating system. In response, (Yang, Liu, & Tran, 2018), (Rooshdi, Rahman, Baki, & Majid, 2014) and (Eisenman & Meyer, 2013) studied the adaptation of weightings to better suit local contextuality. Regarding the triple-bottom line, (Wu, Xia, Zhao, & Pienaar, 2015) stated that sustainable road projects provide a superior performance in terms of economic, social and environmental sustainability. However, (Flores, Montoliu, & Bustamante, 2016) state that this is not always the case. (Diaz-Sarachaga, Jato-Espino, Alsulami, & Castro-Fresno, 2016) and (Peters, 2017) found that environmental considerations dominated SRS considerations, and (Furberg, Molander, & Wallbaum, 2015) and (Peters, 2017) found that social sustainability indicators should be better included. Concerning whole life-cycle considerations, (Flores et al., 2016) also state that some SRS do not cover all project life-cycle phases. This was reinforced by (Bueno, Vassallo, & Cheung, 2013) who identified that the life-cycle considerations of SRS are limited mainly to the construction process. Similarly, (Alam & Kumar, 2013) found that certain high-impact considerations, usually modelled in life-cycle assessment (LCA), are lacking from SRS.

Therefore, considering the high impact potential of these systems, the current lack of clarity on the SRS market and the uncertainty associated to these systems, the aim of this review was to analyse the most prominent rating systems on the market to compare and contrast their functioning. Through this aim, it will be possible to gain clarity on these systems, identify the most suitable system, and understand any benefits or drawbacks associated to the current SRS market. This aim will be achieved by providing a general overview of the systems, and then a more specific analysis on the category and indicator weightings, three-pillar adherence and life-cycle considerations. This study will also focus on the most updated version of the SRS, given they have undergone various updates since their conception; potentially leading to changes in the aforementioned areas of uncertainty. Through these research focuses it will be possible to gain transparency on more environmentally and socially beneficial criteria for smarter roadways.