Increasing travel demand, and challenges associated with high percentages of left-turning vehicles, have encouraged the introduction of significant infrastructure advancements. Certain alternative intersection designs, such as continuous flow intersections, median U-turns, and jughandles, eliminate the traditional protected left-turn, increasing the intersection's optional efficiency. While the design and operations of these intersection types have been studied to varying degrees, their safety and emissions-related impacts are not well-understood.
This project develops a series of microsimulation models for two continuous flow intersections (CFI) located in Missouri and Colorado, and uses the Surrogate Safety Assessment Model (SSAM) to determine the impact of those designs on the location and type of conflicts compared to conventional signalized intersections. Additionally, an emissions model, CMEM, was used in the analysis of the Colorado study site to determine whether CFIs have the potential to reduce emissions compared to conventional signalized intersections.
As hypothesized, the number of total conflicts did decrease upon installation of a CFI for both study sites, despite lane-change conflicts experiencing an insignificant increase at the Loveland, CO study site. While too small of a sample size to provide a definite validation of SSAM, these results show SSAM can accurately predict the types of conflicts likely to occur as well as indicate a reduction in total vehicle conflicts when a conventional signalized intersection is converted into a CFI.
Emission rates per mile at the CFI were lower than those at a conventional signalized intersection, most likely due to fewer total stops and lower delay times for users. The CMEM analysis was repeated for four other volume scenarios, varying left-turn demand. Under all scenarios, the CFI performed better than the conventional signalized intersection. This improvement increased as volume increased, showing that the environmental performance of a CFI is less sensitive to demand than a conventional signalized intersection.
This project set forth to quantify sustainability benefits to the installation of a CFI for practitioners. Ultimately, this research can aid transportation decision-makers by providing quantitative evidence that CFIs can improve the safety impacts for vehicle users and environmental impacts for the general population in both rural and urban applications.