Maximizing Intersection Capacity through Unconventional Geometric Design of Two-Phase Intersections

Typical four-phase, four-legged intersections often operate inefficiently and severely restrict vehicle throughput, and thereby cause large delays. These configurations are limited by traditional geometric design. Altering the geometry of the entire intersection can significantly increase the capacity. Two-phase intersections employ an unconventional lane arrangement to maximize vehicular throughput. This arrangement involves displacing left-turn lanes across opposing through traffic before the main intersection is reached. Such an alteration allows left and through vehicles to proceed simultaneously; consequently, the intersection capacity is improved and delays decrease. Numerous studies have validated the operational improvements associated with such a geometric design, but in-depth analysis of this unconventional system can provide a maximized effect. This paper proposes an improvement to the geometric design and develops an optimization model of a two-phase intersection to increase intersection capacity. After main objective functions and a list of constraints were defined, preliminary tests were performed to show the effectiveness of the method in adapting to changes in traffic demand. The results from the optimization were used to run simulation tests that compared the capacity and delay at a two-phase intersection with those of a conventional four-legged geometric design. The results of several trials strongly showed the optimum performance of the proposed unconventional geometric arrangement.