Improving Traffic Operations at Service Interchanges using the New Offset Diamond Design

This paper proposes the new offset diamond interchange (ODI) as an alternative design which shows potential in mitigating the limitations of failing service interchanges in relation to traffic operation. Vehicle travel time was considered as the primary measure of effectiveness (MOE) for the traffic operation analysis, while the maximum queue lengths were also analyzed. A comprehensive series of VISSIM simulation scenarios was conducted to evaluate the new ODI design in different situations of traffic demand, turning-traffic ratios, traffic distribution, and traffic composition. The results were compared with five existing and four other new interchange designs. The new ODI performed statistically significantly better than all existing designs, including the conventional diamond, parclo A, and the diverging diamond interchange (DDI). The ODI design was found vulnerable in relation to the maximum queue produced in high turning conditions with the unbalanced traffic distribution; however, the threat could be diminished by increasing the storage lengths about 80 ft. Right-of-way (ROW) costs may make the ODI a poor alternative in replacing a standard diamond, but since the ODI fits the footprint of a parclo A it could work well in replacing those interchanges.