Sustainable Pavement Construction: Developing a methodology for integrating environmental impact into the decision making process

Sustainability and specifically environmental stewardship are emerging as prominent issues in engineering decision-making. Despite this, the United States has neither a national policy on sustainability, nor a national sustainable transportation strategy. In many cases this has resulted in state DOTs basing their environmental practices on requirements set out previously by EPA regulations with little or no additional consideration of environmental effects.

A survey conducted as part of this thesis revealed that environmental stewardship is not considered part of current DOT pavement management engineers' job responsibilities, despite having duties such as pavement design and maintenance which can greatly affect the environmental impact of a project. Initial cost and engineering judgment were the most widely considered in decision-making, with LCCA also being considered at least some of the time by most respondents. Environmental impacts, on the other hand, are not often integrated into formal decision making and are more likely to be considered as a "tie breaker" when alternatives have similar costs.

The literature review also covered two distinct types of environmental decision support tools: Environmental Rating Tools and Environmental Impact Calculators. Rating Tools gather predominantly environmental impact information in order to award a score to a project. Environmental Calculators are software tools that use material or equipment inputs to estimate the amount of pollutants produced by a project. While a variety of environmental impact tools are currently available they suffer from drawbacks such as incomplete or unclearly defined LCA boundaries, consideration of only one environmental impact, subjectivity, lack of transparency, out-of-date databases, and an inability to perform probabilistic calculations. CO₂e was the only environmental factor considered by nearly all Environmental Calculators reviewed as part of this thesis and was a major focus of the Rating Tools.

The thesis proposes the framework for a tool that addresses some of the limitations of available tools and aids decision-makers in incorporating environmental factors into roadway decision-making. The proposed tool would address many of the limitations of previous environmental impact calculators and could be implemented without the need for extensive additional research. The tool would calculate emissions due to material extraction and production, emissions due to construction activities, resource consumptions, and emissions due to work zone delays. Emissions due to work zone delays are not considered by any other currently available tool. The tool would also perform probabilistic calculations and have a database which could be added to and updated by users. Additional products developed as part of this thesis are a review of currently available environmental impact tools and a Microsoft Excel workbook used to demonstrate the intended usage of the tool.

It is concluded that the development of such a tool is necessary and feasible. The proposed tool would address limitations of available tools by considering more than one environmental impact, including the previously neglected impact of emissions due to work zone related delay, pairing a user-friendly interface with an editable database, and supporting probabilistic calculations. Recommended future research includes surveying state DOT engineers to determine the barriers delaying implementation of currently available environmental impacts tools. Further benefits could be realized by programming the proposed tool and building a database that reflects the materials, mixes, and construction activities available to a specific locality.