Travel Time and Cost-Benefit Evaluation of Alternative Intersections with Three-Critical-Phase Traffic Signals in North Carolina

Abstract This paper explores the potential benefits of three-phase intersections as a compromise between two-phase and conventional four-phase designs, particularly in terms of improving travel time efficiency and safety. While two-phase intersections offer advantages in reducing travel time and enhancing safety under near-capacity traffic conditions, they are often unpopular due to unfamiliarity and their impact on accessibility, especially when there is high redirected traffic demand from the minor road. Three-phase intersections may address these limitations by combining some of the benefits of two-phase intersections, while they only remove one of the signal phases. This study evaluates six case study sites in North Carolina using traffic microsimulation to assess the performance of nine proposed three-phase alternative intersection designs, including two versions of partial median U-turn (MUT), partial displaced left turn (DLT), reverse reduced crossing U-turn intersection (reverse RCUT), a partial DLT/MUT combination, thru-cut, seven-phase, and redirect left and through (redirect L&T) designs. A benefit-to-cost (B/C) analysis was conducted to quantify the costs and travel time savings associated with each design. Results indicate that three-phase designs generally offer noteworthy improvements in travel times savings over conventional four-phase designs, especially in locations with specific traffic patterns and demand levels. Three-phase designs could also result in lower travel times than intersection designs with two-phase signals at case study sites with significantly high traffic demands. The findings emphasize the importance of tailoring intersection design to site-specific conditions and suggest that three-phase intersections may serve as a cost-effective solution for enhancing operational performance from the cost-benefit analysis. The findings of this study are intended to assist state DOTs in selecting and designing optimal intersection configurations.