Pavements

Considerations In Evaluating Sustainability Impacts Of Preservation Treatments For Asphalt And Concrete Pavements

Diminishing budgets and recognition of the benefits of considering life-cycle costs have motivated changes in agency policies that advocate financial and environmental sustainability through the practice of pavement preservation. Pavement preservation is inherently a sustainable activity. It often employs low-cost, low-environmental-impact treatments to prolong the life of the pavement by delaying major rehabilitation activities. This conserves energy and virgin materials while reducing GHG emissions over the life cycle. Furthermore, well-maintained pavements provide smoother, safer, and quieter riding surfaces over a significant portion of their lives, resulting in higher vehicle fuel efficiencies, reduced crash rates, and lower noise impacts on surrounding communities, which positively contributes to their overall sustainability.

Pavement preservation is primarily concerned with minimizing the project-level life-cycle cost to the agency. To minimize the agency life-cycle cost, only the materials and construction phases of the pavement life cycle are considered, since use-phase costs (primarily vehicle operating costs) are mostly borne by pavement users and not by the agency. For low-volume roads, where the environmental impact of vehicle operations is small, improvements in the agency life-cycle cost and improvements in sustainability are generally compatible, since the objective for both is to minimize the frequency of treatment applications and the amount of material used for each treatment. Therefore, for low-volume routes, the general strategy for improving sustainability is to minimize the amount of materials used and the number of construction cycles over the life cycle by optimizing the treatment selection and timing to avoid major structural damage while minimizing costs.

For higher-traffic volume roadways, the environmental impact of the use phase becomes increasingly important, often to the point that, for very high-volume routes, the materials and construction phase impacts of maintenance and preservation become very small relative to the influence of pavement smoothness, macrotexture, and stiffness on vehicle operations (primarily in terms of fuel economy). Depending on the route, the optimization of the environmental benefit will require balancing the impacts incurred to keep the pavement in good condition (in order to reduce vehicle operating costs) with the impacts resulting from materials production and construction of the treatment. The optimization of environmental benefits for high-volume routes is, therefore, much more complex than it is for low-volume routes because it may increase agency economic life-cycle cost as the need for more frequent treatment is increased to maintain conditions that reduce road user costs and vehicle-produced emissions.

Tables 1 and 2 provide a qualitative summary of the impacts of several asphalt and concrete pavement preservation and maintenance treatments on pavement sustainability. For more details, see Chapter 7 (.pdf) of the Reference Document.