State Of The Practice On Sustainability Rating Systems
A sustainability rating system is essentially a list of sustainability best practices with an associated common metric. This metric, usually points, quantifies each best practice in a common unit. In this way the diverse measurement units of sustainability best practices (e.g., pollutant loading in stormwater runoff, pavement design life, tons of recycled materials, energy consumed/saved, pedestrian accessibility, ecosystem connectivity, and even the value of art) can all be compared. In its simplest form, a rating system can count every best practice equally (e.g., all worth one point), in which case the rating system amounts to a tally of the number of best practices used. In more complex forms, rating systems weight best practices (usually in relation to their impact on sustainability or priority), which can assist in choosing the most impactful best practices to use given a limited scope or budget.
Currently there are a number of national and international rating system efforts within the transportation community. These systems vary in scope and complexity but are generally designed to provide guidance, scoring, and potential rewards for the use of sustainability best practices. Rating systems usually concentrate on practices that are compatible with current regulations but are above and beyond existing minimum regulatory requirements. Rating systems are particularly appealing because they:
- Provide a common metric (points) for the entire range of sustainable solutions.
- Measure sustainability and thus make it manageable.
- Allow for straightforward communication of sustainability goals, efforts, and achievement.
- Provide a reasonable context within which designers, contractors, and material suppliers can be innovative in their solutions.
While there has been and continues to be much debate over the scientific merit and basis for rating systems, such debate can miss the point. The essential purpose of most sustainability rating systems is not a scientifically defensible taxonomy of sustainability, but rather a tool to (1) encourage sustainability practices beyond the regulatory minimum, and (2) to communicate sustainability in a comprehensible manner. In particular, rating systems provide an understandable way to communicate sustainability whether it is within an agency or project, to design and construction professionals, or to the general public. Furthermore, rating systems are often turned to when other means of quantification (e.g., LCA) fail to capture the full range of sustainability best practice impacts. For instance, while LCA is capable of accounting for GHG emissions associated with pavement construction, it is not able to capture more abstract, yet important, sustainability features such as ecological connectivity and aesthetics.
Rating systems are often criticized because (1) they tend to sacrifice detail for simplicity, (2) it is difficult to generate consensus on which items to include/exclude, (3) they do not capture the entire scope of sustainable solutions, and (4) their use in blindly pursuing points as part of a rating system could trump good design/construction. However, a well-designed rating system used within a proper organizational approach to sustainability can overcome these issues and provide value to the agency or organization.
Rating Systems in Context
It is important to view a rating system in the right context. For instance, project-based rating systems address sustainability within the context of an individual project. Therefore, they should be considered specialized tools that fit within a broader agency approach to sustainability but do not address all agency sustainability efforts. In this context, the adoption or use of a rating system does not supply sustainability but rather complements other agency-wide efforts.
Rating Systems Relevant to Pavements
While there are many rating system efforts that apply in some way to pavements worldwide, the following sections briefly outline those systems that are (1) the most prevalent on the national stage in the U.S., and (2) most relevant to pavements. Note that although all of these rating systems are relevant to pavements in some way, none of them are focused on pavements as the primary system under consideration. All focus on larger systems (e.g., road project, agency sustainability efforts, neighborhood design, infrastructure systems) and account for pavement as a contributing subsystem. Therefore, none of them should be used to rate or grade pavement sustainability in isolation because pavement tends to exist as a subsystem that contributes to larger systems (e.g., neighborhood, highway corridor, downtown street network, community, ecology).
INVEST (Infrastructure Voluntary Evaluation Sustainability Tool)
INVEST (FHWA 2011; Bevan et al. 2012) is a sustainability rating system for roadways that encompasses planning and policy, project development, and operations and maintenance. It is point based and voluntary and applicable to all U.S. road projects with a focus on state Departments of Transportation (DOTs) and Metropolitan Planning Organizations (MPOs). INVEST was created by the FHWA as a self-evaluation tool. There are no plans to make it required in any context. INVEST has three different subsystems that can be used independently: Systems Planning, Project Development, and Operations and Maintenance. INVEST is intended to function as a self-certification program (i.e., the project owner can also perform the review).
Greenroads (Muench et al. 2011) is a sustainability rating system for roadway design and construction. It is point based and voluntary and applicable to all U.S. road projects. Relevant characteristics are given below. Greenroads was originally created by the University of Washington and CH2M HILL in partnership, now independently owned and operated by the Greenroads Foundation, and also includes an individual accreditation program. Greenroads is a third-party certification program (i.e., the Greenroads Foundation functions as an independent third party review).
Envision (ISI and Zofnass 2012) is a sustainability rating system for civil infrastructure. It is point based, voluntary, and applicable to all civil infrastructure. Important characteristics are listed below. EnvisionTM has some features in common with CEEQUAL (a U.K.-based system). It also includes individual training and accreditation.
GreenLITES (Leadership In Transportation and Environmental Sustainability) is a rating program for transportation infrastructure (NYSDOT 2010). The Project Design Certification Program is used as a design review for NYSDOT projects (NYSDOT 2012). The Operations Certification Program began piloting in 2009. Both are self-certification programs meaning the NSYDOT does the project work and the certification review.See Chapter 10 (.pdf) of the Reference Document for more details.
Bevan, T., L. Reid, A. Davis, T. Neuman, K. Penney, S. Seskin, M. VanZerr, J. Anderson, S. Muench, C. Weiland, T. Ramani, J. Zietsman, J. Crossett, C. Crocker, and J. Schulz. 2012. INVEST: Sustainable Highways Self-Evaluation Tool. Version 1.0 (.pdf). Federal Highway Administration, Washington, DC.
Federal Highway Administration (FHWA). 2011. Sustainable Highways Self-Evaluation Tool: Compendium of System Planning and Processes, Project Delivery and Operations and Maintenance Criteria-Pilot Test Version. Federal Highway Administration, Washington, DC.
Institute for Sustainable Infrastructure (ISI) and Zofnass Program for Sustainable Infrastructure at the Harvard University Graduate School of Design (Zofnass). 2012. Envision, Version 2.0. A Rating System for Sustainable Infrastructure. ISI, Washington, DC.
Muench, S. T., J. L. Anderson, J. P. Hatfield, J. R. Koester, and M. Soderlund. 2011. Greenroads Manual. Vol. 1.5. University of Washington, Seattle, WA.
New York State Department of Transportation (NYSDOT). 2010. GreenLITES Project Design Certification Program, Version 2.1.0. New York State Department of Transportation, Albany, NY.
New York State Department of Transportation (NYSDOT). 2012. 2012 GreenLITES Draft Operations Certification Program. New York State Department of Transportation, Albany, NY.