Pavements and the environment: A life-cycle assessment approach

The relationship between pavements and the environment is largely unquantified. Using life-cycle assessment as the evaluation framework, the impact from pavements can be quantified in order to uncover ways to minimize the environmental footprint of this vast civil infrastructure system. Research exists that begins to understand the relationship, but falls short of comprehensively characterizing the impact. Expanding our knowledge and sharpening our modeling are critical steps that the research presented here takes to support the creation of more sustainable pavements. The lack of a comprehensive methodology with which to evaluate the impact of pavements is a significant shortfall which plagues the existing research. Pavements affect the environment not only during the manufacturing and placement of materials, but also through traffic delay, rolling resistance, the urban heat island effect, and other impact mechanisms. While these commonly excluded components may be less obvious, they are no less important and have the potential to be influential contributors to the overall life-cycle impact. This research proposes a comprehensive methodology that includes the known components of the pavement life cycle. Although data availability, applicability of the components, and other project constraints will ultimately dictate the boundaries of a particular assessment, beginning with a comprehensive methodology offers practitioners the opportunity to make decisions based on discretion rather than ignorance. This will result in more equitable comparisons and functional conclusions that can be more confidently implemented in creating more sustainable pavements. The ability to improve the environmental performance of pavements depends not only on using a comprehensive methodology, but also on having an in-depth knowledge of the components which comprise the life cycle. Research areas outside of the existing pavement life-cycle assessment literature may contain the best available information on the impact of individual components on the environment. Using global warming potential as the environmental indicator, ranges of impact for each component are calculated and compared based on the information uncovered in the research review. The relative impacts between components are found to be orders of magnitude different in many cases. For instance, the impact from rolling resistance has the potential to be four orders of magnitude larger than that of onsite equipment. By focusing improvement efforts on those components with large impact potentials, environmental performance can be improved more effectively. A strategic method to lowering the global warming potential of a pavement is developed based on this concept. The approach prioritizes evaluating components with high impact potential so as to maximize the efficiency and effectiveness of environmental improvements. It takes advantage of the fact that small changes in high-impact components will have more effect than large changes in low-impact components. Finally, life-cycle assessment is used to evaluate the benefits and drawbacks of long-life pavements. Improved pavement design tools have made it possible to increase design lives to 100 years. This research examines whether designing pavements to serve extended periods of time is an environmentally beneficial practice. The results indicate that long-life pavements may not always be the best option due to the long periods of time before the benefits are realized. Roadway segments that will predictably support high traffic levels into the future are prime candidates for long-life designs. Conversely, segments with wavering, inconsistent demand are better served by pavements with more traditional design lives. These generalized scenarios demonstrate that long-life designs should not be ubiquitously applied to all new pavement construction, but rather to select pavements that offer the best chance of lowering life-cycle environmental impact.