Evaluation of Variables Affecting Sustainable Highway Design with BE 2 ST-in-Highways System

The Building Environmentally and Economically Sustainable Transportation-Infrastructure-Highways (BE²ST-in-Highways) sustainability rating system was developed to provide a quantitative methodology for rating the benefits of sustainable highway construction. The methodology is grounded in quantitative metrics so that a transparent linkage exists between the project rating and the sustainable practices employed in design and construction. This rating system can be employed by the highway construction industry and agencies to evaluate sustainable practices quantitatively and to incorporate sustainable elements into projects. To illustrate how BE²ST-in-Highways is employed, 10 alternative designs were evaluated and compared with two reference pavement designs for a pilot project (Baraboo Bypass, Wisconsin). The results of this pilot project evaluation indicate that the use of recycled materials instead of conventional materials in highway construction can improve sustainability considerably: about 27% reduction in global warming potential and energy and water use. Reductions in carbon dioxide emissions and energy and water consumption are largely due to the reduction of the material production phase (e.g., mining and processing) by substituting existing recycled materials and reducing the thickness of the base layer and the number of rehabilitation events due to longer service life because of superior properties. Use of recycled material resulted in reductions in the life-cycle cost by as much as 30%. Using recycled materials in the surface layer is not the use with the highest value. Using recycled materials in the base course is thus more advantageous and has higher value because larger material quantities are involved in the base course with greater potential for cost savings, as shown in this case study.