Challenges for Sustainability Assessment by Indicators

Different methods have been developed to achieve an integrated sustainability value using multiple indicators. Essentially, what is stated in developed standards (and under development; e.g., the International Organization for Standardization’s [ISO’s] TC 59/SC 17 standards for sustainability in buildings and civil engineering works) is the determination of a sustainability indicator set and its implementation, evaluation, and control over the project life cycle from design, through construction, operation, and maintenance, to demolition (end of life). Project alternatives can be classified according to their sustainability by applying these indicators and therefore establishing whether the targets posed by the indicators are satisfactorily achieved.

An indicator set must describe sustainable construction through its social, economic, and environmental pillars of sustainable development and in consideration of the relationships among these pillars; additionally, selected indicators should describe the essential impacts on the three pillars, and their selection must be justified, reasoned, and validated. Finally, the development process and application of indicators must be fully transparent (ISO 2006).

According to Bell and Morse (2008), there are two methods for integrating different indicator values to achieve a sustainability index:

In addition to these analytical techniques, there are several other ways to approach sustainability. One is the “binary view”: whether a project is sustainable or not. Another approach is to grade sustainability from the lowest to the highest level. This approach is the most commonly applied in the construction sector. Thus, the LEED (Leadership in Energy and Environmental Design; U.S. Green Building Council) rating has four levels (certified, silver, gold, and platinum) indicating the sustainability of a building, the SBTool (International Initiative for a Sustainable Built Environment) uses five levels from 1 to 5, CASBEE (Japan Sustainable Building Consortium) has levels from 1 to more than 3 according to the ecoefficiency value, and so on. It is more important to detail how sustainable a project is rather than to analyze whether the project is sustainable or not, perhaps because it is unclear whether the variables assessed can absolutely define a project as sustainable. It is easier to determine which projects have a greater or lesser degree of sustainability according to an indicator set.

Sustainability assessment may also have different outcomes. The most commonly used is the spider or radar diagram, which expresses the valuation of a project or alternative in relation to each indicator or dimension (see Figure 1 for an example of a spider diagram illustrating areas or dimensions of sustainability). The diagram has as many axes as dimensions measured—for example, water, energy, atmosphere, society, economy, land, biodiversity, and so on—and shows the value obtained for each dimension. Impacts may also be included in such diagrams; each axis would correspond to a different impact. New developments in sustainable building are centered on this kind of impact assessment (Macías and García Navarro 2010). There is also the possibility of integrating all ratings for each criterion into a single value or index by applying cost–benefit or multicriteria methods. Generally, existing tools include this result as the most visual and simplest, even in spite of significant error due to the mix of units and scales in the same value.

Practical application of sustainability indicators in civil engineering projects, as in other sectors, requires attention to the following:

The establishment of sensitivity ranges is probably the most complex task. Maximum and minimum possible values need to be established for each indicator, and these two values must be normalized in a range of standard scores—for example, [0, 1]. Value functions are usually used to reach a minimum to maximum score, considering the effort to improve the rating of each indicator; depending on the indicator characteristics, different functions can be used (see Figure 2). The exponential function is used when looking for an analysis in which the improvement of initial values is simple and seeks to reward efforts to improve the indicator near the maximum. The logarithmic function is used for those criteria for which a small effort to improve its valuation increases its score substantially, whereas an improvement near the maximum value does not produce a significant increase in score. The linear function, with a simple line between the maximum and minimum points, is used when looking for a linear rate between improvement effort and the final score. Finally, the discontinuous function is used when there are set fixed levels of effort.

Checklists are based on discontinuous functions. If the criterion is met, one point is obtained, and if it is not, the criterion is not scored. For example, for the indicator water use reduction used by LEED–NC (Version 2.2; U.S. Green Building Council 2005), reducing water consumption by more than 20% is 1 point and by less than 20% is 0 points. However, indicator sets are generally based on continuous value functions that assign a better indicator value when a greater effort is made, depending on each criterion.

Because sustainability indicators are usually new, emerging criteria, the biggest problem is frequently the establishment of these maximum and minimum values. They are typically not legislated and vary dramatically over time. For these reasons, it is very important to continuously monitor and use a feedback system after each indicator’s assessment in order to validate established ranges. An alternative is to measure a standard project and use its results as a benchmark against which to compare.

Society and stakeholders are increasingly concerned about the impact of construction projects on the environment, society, and the economy. To enable the implementation of new sustainability criteria that will enhance positive impacts and reduce negative impacts, operational tools and procedures are required. We have outlined some of the sustainability indicator systems that are currently available in civil engineering and described what we see as the key issues in their application if indicators are to become the definitive way to measure sustainability. It is also vital to form a consensus on sustainability assessment: What is a sustainable project? Additionally, what are the key sustainability variables and indicators that must be measured? Adopting lessons learned in similar fields such as building and urban planning, which have two decades of experience in developing sustainability assessment tools, may be a first step in answering these questions. There is also a need for the development of general standard procedures in sustainable project management.

Sustainability criteria are becoming a requirement in project management that is important to society, and government and promoters have committed to using them. Indicators can be a great aid in sustainable management of engineering projects, opening new opportunities to achieve added value in infrastructure projects.