This report presents a comprehensive review and assessment of current ‘alternative intersection’ methods which successfully eliminate the left-turn phase. The left-turn phase can reduce intersection efficiency considerably. With increasing traffic and limited resources, the Department of Transportation moves forward with a vision of optimizing intersection control through the implementation of innovative intersection designs through the Transportation Systems Management & Operations (TSM&O) program. TSM&O is an established program used to enhance the performance of multimodal infrastructures. The purpose of this program is to improve safety as well as capacity, reduce congestion and delay, and improve the travel time reliability along all modes of transportation. This project assessed the operational benefits and challenges. In addition, considerations were made for the evaluation of safety for bicycles and pedestrians utilizing these alternative intersections. The TSM&O program has over dozen strategies that aim at improving travel time reliability and reducing delays. The main objective of this research was to evaluate the benefits of six different alternative intersection treatments and develop an evaluation matrix for the design criteria and placement of the following alternative treatments: Continuous Flow Intersection (CFI) Diverging Diamond Interchange (DDI) Median U-Turn (MUT) Restricted Crossing U-Turn (RCUT) Quadrant Roadway Intersection (QRI) Roundabouts Operational analysis and studies presented regarding these alternative designs proved that they outperform most conventional intersections and enhance the arterial flow of traffic. Although there is not much field data available for some of these new designs, micro-simulation analyses showed that they are effective at improving safety and efficiency, which are usually two conflicting goals. The analysis highlighted several important aspects regarding CFI traffic operations in the case of unbalanced volumes and demonstrated how partial CFI intersections can improve the overall intersection performance at various demands. The CFI also proved to outperform the conventional intersection. It is crucial to consider critical movements in the CFI design; this is where the most operational benefit lies. The analysis also showed that significant throughput improvements were observed at high volume levels, with 25 percent increase in capacity. The MUT intersection operations showed an improvement in the performance when compared to the existing condition. The design significantly reduced the number of conflicts at the main intersection. The two-phase signal timing plan provided higher percentage of green time for each of the through movements. However, the left-turn movements are susceptible higher delay and travel time due to their indirect movement through the U-turn crossover. Wayfinding is very important at MUT intersections, especially for left-turning drivers who are not familiar with the intersection. The MUT design outperformed the conventional intersection in terms of delay and travel time for increased volume level as well. The analysis also demonstrated how RCUT can improve the overall performance compared to the existing conditions. The RCUT intersection reroutes the through and left-turn movements from the minor streets to the median U-turn crossover, providing an easier maneuver at the major street. The intersection design significantly reduces the number of conflicts at the main intersection. Only two phases are required at the main intersection to accommodate the vehicles and pedestrians, which ensures a better operation at the major street. However, the tradeoff is that the movements on the minor road may exhibit higher delay and travel time due to their indirect movement using U-turn crossover. Vehicle-pedestrian conflicts are reduced significantly using a “Z” shaped crossing in RCUT intersection. The case study showed that RCUT intersection reduced the overall delay and travel time, and improved the level of service compared to a conventional intersection. The DDI traffic operations analysis showed that it is best suited for conventional diamond interchanges with heavy left-turn volumes as well as unbalanced volumes. It also demonstrated how DDI can improve the overall performance compared to a CDI. Based on the DDI conflict analysis, traffic safety was improved significantly due to the reduction in the number of vehicle-to-vehicle conflicts. DDI also reduced the delay of all left-turn movements and improved the overall level of service for both approaches of the crossover intersections. QRIs are applicable mainly at intersections with busy arterials. The design approach reroutes all four left-turn movements in the four-legged intersection using a secondary roadway. The elimination of the left-turn lanes at the main intersection provides a shorter crossing distance for pedestrians and bicyclists. The case study showed that QRI intersection reduced the overall delay and travel time, and improved the level of service compared to the conventional intersection. Alternative intersection treatments lower the number of conflicts at intersections and help reduce overall congestion. While these alternative designs are noticeably different from each other in approach, there is a common aspect among them. They attempt to remove one or more of the critical conflicting movements from the major intersection and divide the intersection into smaller networks that would operate in a one-way fashion. Thus having fewer signal phases with shorter signal cycle lengths, shorter delays, and higher capacities compared to conventional intersections. They have been successfully implemented in Utah, North Carolina, Missouri, and Louisiana. The overall analysis provided a variety of parameters that need to be considered when implementing any of these designs. These intersections can be significantly cumbersome for vehicles, bicyclists, and pedestrians to navigate without the proper implementation of wayfinding signs and education of the road users. However, the benefits of these designs, when applied properly, can save municipalities years of capacity and preserve the existing infrastructure for a longer period of time. These goals align with the overall goal of the FDOT TSM&O program. (Author/publisher)
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