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Although the concepts of the crossover displaced left-turn (XDL) intersection (also called the continuous flow intersection) were developed approximately four decades ago, there is no simplified procedure to evaluate its traffic performance and to compare this intersection with conventional intersections. Several studies have shown the qualitative and quantitative benefits of the XDL intersection without providing accessible tools for traffic engineers and planners to estimate average control delays and queues. Modeling was conducted on typical geometries over a wide distribution of traffic flow conditions for three different design configurations or cases using VISSIM simulations with pretimed signal settings. Some comparisons with similar conventional designs showed considerable savings in average control delay, as well as average queue length and increase in intersection capacity. The statistical models provided an accessible tool for the practitioner to assess average delay and average queue length for three types of XDL intersections. Finally, a preferred signal setting was developed for each of the five intersections of the XDL network.

Transportation planners and traffic engineers are facing the challenge of inventing ways to mitigate congestion during the peak hours. Alleviating delays and improving safety for passengers and pedestrians is the primary motive. One way of achieving this objective is to search for alternative intersection and interchange designs. This paper presents the results of a study on two new alternate designs-Double Crossover Intersection and Diverging Diamond Interchange. These designs are studied for different traffic scenarios using traffic simulation and the results showed better performance during peak hours when compared to similar corresponding conventional designs. Better performance includes better level of service, lesser delays, smaller queues, and higher throughput. BACKGROUND Transportation planners and traffic engineers are facing the challenge of mitigating congestion during the peak hours and at lower costs. Alleviating delays and improving safety for motor vehicles and pedestrians are primary motives. In urban areas the land available for constructing roads is less and hence should be used more judiciously by designing roads, intersections, and interchanges that occupy less right of way. One way of achieving all these objectives is to search for alternative intersection designs. Researchers have developed several innovative intersection designs in the past to address these problems. These designs include the quadrant roadway intersection, median U-turn, superstreet median, jughandle, split intersection, and the continuous flow intersection (CFI). The most influential factor in the intersection performance for heavy flows is achieved by reducing the number of phases in the signal cycle. The CFI especially is finding increasing acceptance in the United States lately (1). Chlewicki (2) suggested two new designs for intersection and interchange designs-the Synchronized Split-Phasing (SSP) Intersection and the Diverging Diamond Interchange (DDI). As in the CFI, SSP design also disperses the flow of traffic before reaching the main intersection. The synchronized split phasing design allows both the through and the left movements to cross over prior to the intersection. (see Figure 1(a)) The main goal of the DDI design is to better accommodate left-turn movements and hence eliminate a phase in the signal cycle. Figure 1 (b) shows the layout of the diverging diamond interchange. The freeway portion does not change but the movements off the ramps change for left-turns. In a DDI, through and left-turn traffic on the crossroad maneuver differently from a conventional diamond interchange as the traffic crosses to the opposite side in between the ramp terminals. Chlewicki (2) discusses the simulation tests performed for a case study intersection and interchange using Synchro as the simulation tool. Results showed that the SSP and DDI designs outperform similar corresponding conventional designs. In his conclusion, Chlewicki (2) discusses the future scope of research including analysis of different volume ratios and tu...

No abstract

Transportation planners and traffic engineers are facing the challenge of inventing ways to mitigate congestion during the peak hours. Alleviating delays and improving safety for passengers and pedestrians are the primary motives. One way of achieving these objectives is to search for alternative intersection and interchange designs. This paper presents the results of a study on two new alternate designs: double crossover intersection and diverging diamond interchange. These designs were studied for different traffic scenarios with the use of traffic simulation, and the results showed better performance during peak hours than that of similar corresponding conventional designs. Better performance includes better level of service, shorter delays, smaller queues, and higher throughput.