Assessing different freeway interchange design impacts on traffic emissions and fuel consumption through microsimulation

When evaluating different roadway design alternatives, environmental impacts attributed to vehicular emissions should be considered as significant as their traffic safety and operational performances. In today’s world we are aware of the impacts of climate change and global warming. As freight and passenger travel demands increase, so does congestion and emissions from transportation vehicles, which have drawn a significant attention in recent years. Transportation is the highest contributor to U.S. greenhouse gas (GHG) emissions by economic sectors. Vissim emission calculator provides an opportunity to perform a comparative emissions analysis. This paper summarizes a case study of an existing service interchange, a conventional diamond interchange (CDI) at Austin Blvd on I-75 located 12 miles south of downtown Dayton, Ohio with other two alternative designs, a diverging diamond interchange (DDI) and a single point urban interchange (SPUI), in terms of fuel consumptions, emissions, and traffic operations for similar traffic conditions, and roadway characteristics through microsimulation. In this study we focused on three critical pollutant gases emitted from vehicles’ exhaust pipes, i.e., carbon dioxide, carbon monoxide and nitrogen oxides, including fuel consumption. In addition, the study selected average stopped delay and average queue length for traffic operations measures of effectiveness (MOEs) because these two reflect all others in terms of the expected trends and expectations. The signal optimization for each interchange was conducted utilizing PTV Vistro and traffic simulation and emissions analysis using PTV Vissim. The results indicate that the existing CDI design results in much higher emission rates than the SPUI and the DDI for each traffic level condition considered. Although the SPUI’s and DDI’s performances were very close, a significant difference was observed at higher traffic volumes. Generally, emissions at the DDI design were lower compared to the SPUI design.