Diverging Diamond Interchange Research Articles

Innovative Method for Remotely Fine-Tuning Offsets Along a Diverging Diamond Interchange Corridor

Diverging diamond interchanges (DDIs) are relatively new in the United States, and signal coordination between the crossovers and adjacent intersections is challenging. This paper provides a method for remotely fine-tuning offsets for a DDI and its adjacent intersections. The proposed method uses the dynamic bandwidth analysis tool (DBAT). The tool uses actuated phase times from the signal controller to optimize the dynamic bandwidth on the basis of that entry data set. Four performance measures evaluated the proposed method: delay, stop severity index, maximum queue, and vehicle trajectory plots. The test results confirmed that DBAT provided a better offset solution than other bandwidth optimization tools that generally optimized programmed bandwidth only and did not account for early return to green caused by skipped or gapped-out movements. Under the DBAT offsets, delay for the through movements on the corridor decreased by 52.8% for northbound vehicles and 46.83% for southbound vehicles. The average delay reduction over all measured paths for uncongested and congested scenarios was 13.88% and 3.50%, respectively. The proposed method and workflow can significantly reduce the offset retiming work process. Normally, this manual process takes more than a day, but the proposed method can be completed in less than an hour without visiting the study site. Furthermore, the proposed method can coordinate any set of movements, as well as multiple travel paths. The authors believe that the proposed method and workflow will significantly help both retiming and new timing of arterial signal coordination along DDI corridors and other signal systems.

Maintenance of Traffic for Innovative Geometric Design Work Zones

In an effort to improve the safety and capacity of existing roads, many transportation practitioners are implementing innovative designs at intersections and interchanges. The development of construction phasing plans for these projects is a critical component for maintaining safety and mobility on the facility during construction. The goal of this study was to address the gaps in existing knowledge by presenting the state of the practice and providing guidance for transportation practitioners in developing construction phasing and maintenance of traffic (MOT) plans for projects with innovative geometric designs. Several types of innovative geometric designs were studied, including the round about, single-point urban interchange, diverging diamond interchange, restricted-crossing left turn, median U-turn, and displaced left turn. Examples of MOT phasing diagrams showing phasing sequencing and construction work areas were developed on the basis of a review of the literature, a survey of practitioners, interviews with industry experts, and a review of actual project plans. The examples of MOT phasing diagrams are intended to serve as a starting point for transportation practitioners, but project-specific factors such as driver experience, availability of detours, traffic counts, adjacent land use, elevation differences, barrier offsets, number of lanes, and anticipated impacts of a possible closure should be considered when deciding on the best MOT methods for a given project.

Simulation model of diverging diamond interchange for Alabama

A diverging diamond interchange is a freeway and arterial interchange design that uses crossovers at the ramp intersections to eliminate conflicts between arterial through traffic and the left turning traffic, from both the arterial and the ramps. The traffic switches which side of the roadway it is travelling, from right to left, at the crossovers. This allows unopposed left turns from the arterial to the ramps. This project will conduct an analysis on a high traffic growth interchange in Alabama by examining the location and adjusting the traffic volumes through a simulation.

Safety Evaluation of Diverging Diamond Interchanges in Missouri

The diverging diamond interchange (DDI) has gained in popularity since its first implementation in the United States in 2009. The operational benefits and lower costs of retrofitting a conventional diamond with a DDI have contributed to increased use of the DDI. Research on DDIs has focused primarily on the assessment of operational benefits. Formal safety evaluations of DDIs are lacking. This study aimed to fill the knowledge gap by conducting a safety evaluation of DDIs using three types of before–after evaluation methods: naive, empirical Bayes, and comparison group. Three evaluation methods were used because each involved different trade-offs, such as data required, complexity, and regression to the mean. All three methods showed that a DDI replacing a conventional diamond decreased crash frequency for all severities. The highest crash reduction (59.3% to 63.2%) was observed for fatal and injury crashes. Crashes involving property damage only were reduced by 33.9% to 44.8%. Total crash frequency also decreased by 40.8% to 47.9%. A collision diagram analysis revealed that the DDI, as compared with a diamond, traded high-severity crashes for lower-severity crashes. Whereas 34.3% of ramp terminal fatal and injury crashes in a diamond occurred in left-turn angle crashes with oncoming traffic, the DDI eliminated this crash type. One potential concern for the DDI is the possibility of wrong-way crashes, but only 4.8% of all fatal and injury crashes occurring at the ramp terminal of a DDI were wrong-way crashes. The DDI offers significant crash reduction benefits over conventional diamond interchanges.

Long-Term Monitoring of Wrong-Way Maneuvers at Diverging Diamond Interchanges

With the popularity of diverging diamond interchanges (DDIs), also called double crossover diamonds, on the rise, there has been a growing concern about the potential for wrong-way maneuvers. With the mainline crossover configuration at this interchange, the risk of vehicles traveling down the wrong direction is one of the most vital and feared public safety concerns at DDIs. This concern is especially important as DDIs are being installed at a rapid pace across the country. As part of an ongoing FHWA research project, a team of researchers was tasked with continuously monitoring five DDIs for 6 months to observe rates and causes of wrong-way maneuvers. The team installed video cameras at each of the DDIs and postprocessed the video by using video detection software; this procedure results in a more efficient method of monitoring the crossovers at these DDIs. The software polls generated by the detection software were manually verified by analysts after the video was processed, and the findings are presented in this paper. The analysis showed that wrong-way maneuvers tended to occur more often when vehicles were first entering the DDI rather than after correctly moving through the first crossover and going the wrong way at the second crossover that they approached (traveling outbound). Likewise, wrong-way maneuvers were found to occur more frequently at night than during the day. The findings show that DDIs do experience a certain level of wrong-way maneuvers; however, no crashes could be identified from safety records that were associated with these events. Consequently, DDIs have generally proved to be safe and efficient movers of traffic when designed appropriately.

Performance Measures for Optimizing Diverging Interchanges and Outcome Assessment with Drone Video

Diverging diamond interchanges (DDIs) are an emerging interchange configuration that eliminates the need for left-turn phases in conventional diamonds and may be less expensive to construct than some alternative geometries. This paper examines signal timing for DDIs. DDI signal timing typically has used a two-phase configuration that reflects the two competing movements at the crossover points at each inter section of the DDI. This configuration inherently contains some inefficiency: (a) there is potential for internal queuing under two-phase configuration and (b) it is possible for the inflow demand to exceed outflow capacity of the interchange. This paper uses high-resolution event data to develop performance measures for evaluating operations at a DDI in Salt Lake City, Utah. Alternatives to the existing signal timing within the two-phase configuration are modeled and tested with a field deployment. The field deployment demonstrated the ability to prioritize ramp or through vehicles within the two-phase configuration. Additionally, a new three-phase configuration was developed and deployed to address the internal queuing that occurs with two-phase timing. With this new configuration, the flows from one DDI intersection to the other are balanced, and progression within the DDI is improved. With the implementation of the three-phase configuration, the percentage of vehicles arriving on green at the heaviest internal movement within the DDI increased from 53% to 92%. To illustrate these performance measures and improved DDI operation qualitatively, a video from a tethered unmanned aerial vehicle demonstrated the vehicle arrival characteristics by overlaying vehicle detection and signal state graphics on the video.

Microscopic Simulation on the Design and Operational Performance of Diverging Diamond Interchange

A proper traffic impact study needs to be conducted in order to estimate the extra traffic volume generated from new development to mitigate the negative impact on existing roads. Generally, results from traffic impact studies indicated that most of the existing intersections in urban areas have already exceeded the capacity. The problem becomes even more complicated when the peak hour flow rates are reaching capacity at the signalized intersections of a diamond interchange. Therefore, this study attempts to search for alternative interchange design to address the problem by means of simulation. This paper elaborates the microscopic simulation models developed using the VISSIM software to investigate the design and operational performance of a diverging diamond interchange for different traffic scenarios and signal plans.

Development of a Signal Optimization Model for Diverging Diamond Interchange

As one of the most popular unconventional interchange designs, diverging diamond intersection (DDI) has received increased attention over the past decade. Through a reverse operation of traffic movements between its two crossover intersections, DDI can accommodate more traffic movements within each phase. To design an effective signal plan for DDIs, one needs to address the following two critical issues: (1) how to select the common cycle length and green splits at each crossover intersection under different geometric conditions, and (2) how to coordinate a DDI’s two crossover intersections with its adjacent conventional intersections. To contend with these issues, this paper presents an optimization model with the objective of maximizing intersection capacity to yield the optimal green splits and cycle length. Also, in view of the potentially large left-turn traffic volumes from the freeway off-ramps, this study has further modified a model to provide progressions to both left-turn and through traffic paths. Using simulation software as an unbiased tool, this study has conducted extensive simulation comparisons between the optimized signal plans and the results from signal optimization software under various traffic scenarios. The experimental results confirm the promising properties of the proposed signal models for DDI, especially if the traffic progression between two crossover intersections is the major concern.

Crossover Roundabouts

The double crossover diamond (DCD) (also known as the diverging diamond interchange) was first introduced conceptually to engineers and planners in the United States less than a decade ago. The concept has been spreading rapidly since that time; as of July 2013, DCDs had been constructed in 19 locations in eight states and had been studied in countless other projects nationwide. Nearby frontage roads pose operational challenges for all interchanges, and DCD geometry intensifies this problem. Reverse curvature for crossover points reduces the storage length between ramps and nearby frontage roads in DCDs. The crossover roundabout concept was conceived as a potential solution to this challenge. Instead of a signalized crossover point (as in a DCD), a five-legged roundabout was proposed for the intersecting arterial, frontage road, and ramps. A crossover roundabout would function essentially like any other roundabout except that it would adjoin an arterial roadway with travel directions flipped on one side. The operational and safety benefits of typical roundabouts are expected to apply to crossover roundabouts; no new driver behaviors must be learned. Variations of crossover roundabout interchanges are possible: one crossover roundabout could adjoin half of a DCD, or two crossover roundabouts could form a complete interchange. Interchanges with two crossover roundabouts would look like typical double-roundabout diamond interchanges with the arterial road directions flipped between the roundabouts. Crossover roundabouts are not required to contain frontage roads to function. Microsimulation and cost estimations have shown the concept to have merit; crossover roundabouts can combine the best attributes of DCDs and roundabouts.

Lane Utilization at Two-Lane Arterial Approaches to Double Crossover Diamond Interchanges

Double crossover diamond (DCD) interchanges, also known as diverging diamond interchanges, are popular and promising alternative interchanges that are increasingly being implemented nationwide. One unique feature of a DCD interchange is that through movements on the arterial road have to cross each other twice to complete their movements, while enabling left-turn movements from the arterial to the freeway to proceed without stopping at the downstream intersection. Consequently, interchanges with heavy left-turn movements are good candidates for DCD implementation. This unique feature of a DCD interchange means that there is a need to research lane utilization at the upstream approach intersection of DCD interchanges, as the lane use could be unbalanced. This unbalanced lane utilization could have a significant effect on operations at the first crossover and the interchange as a whole. This study examined lane utilization factors provided in the Highway Capacity Manual 2010 (HCM) for conventional diamond interchanges and found that they are not generally applicable to DCD interchanges. The study then proposed a lane utilization model calibrated with field data obtained at three DCD sites. The new model fit observed conditions at the DCD sites better than previously developed HCM factors. The model was then validated with three additional DCD interchanges, and validation results confirmed that the new model adequately predicted DCD lane utilization. The authors recommend that DCD interchange designers and analysts use the new model where it is applicable but also that more research be conducted to find lane utilization factors for other DCD configurations.

Diverging Diamond Interchange Analysis: Planning Tool

Many traffic simulation software tools have emerged over the last decade and are widely used for analyzing capacity, delay, and level of service at intersections, ramps, and along arterial/freeway segments. Although these tools have shown great promise, they are expensive and the data collection and input setup is time consuming and resource intensive. Traffic engineers predominantly use one of those tools to analyze a diverging diamond interchange (DDI), also known as double crossover diamond interchange. Developing a simulation model and performing required analysis takes considerable time. Because it is not necessary to obtain a detailed traffic operational analysis of a DDI while interchange alternatives are being developed, a quick and easy evaluation procedure is warranted. In this paper, a critical lane volume (CLV)-based DDI analysis methodology is developed, which could be an appropriate tool to bridge the gap. In this methodology, two intersections or nodes of a DDI, where through-traffic movements along the arterial cross each other, are considered crucial. Understanding of the crossover movements, ramp movements, and coordination of traffic movements between the two nodes and lane configuration are used in developing the methodology. Critical movements are analyzed, compared, and logically added to obtain the CLV of the two nodes. The obtained CLV is used in deriving the level of service of the two intersections in a DDI. The paper describes the mathematical formulation and analysis procedure to evaluate a DDI. Two real-world DDIs are analyzed by using the developed method and compared with simulation results for reliability and accuracy.

Analyzing the Diverging Diamond Interchange Using Discrete Event Simulation

The diverging diamond interchange (DDI) can improve traffic flow by limiting the number of phases in the traffic signals and improve safety by eliminating left turns. A few instillations of these interchanges have been constructed and there is great potential to construct more. In an effort to develop a methodology to evaluate these interchanges, this paper presents the development of a discrete event simulation model of the diverging diamond interchange (DDI). Specific emphasis is on using simulation to model the DDI, a description of the operation of the simulation model, and using simulation to understand the operation of the DDI. The paper concludes that the use of the simulation package allows for rapid evaluation of the DDI and demonstrates that this interchange design will not work in all locations.

Should the Diverging Diamond Interchange Always be Considered a Diamond Interchange Form?

The diverging diamond interchange (DDI) has proved to be an ideal interchange solution because of its safety features, low costs, and operational benefits in different scenarios of turning movement volume. Pre vious studies have compared the DDI with other interchange forms by using the same number of through lanes for each interchange design. Those studies used microsimulation software for the analysis and had a limited number of turning movement combinations to sample. This study considered a large sample of turning movement combinations and compared more interchange configurations to determine whether the DDI might have more applications than previous studies have indicated. A basic form of the critical lane volume method was used to evaluate the different interchange configurations. Although this method is not the most perfect method, there is reason to believe that the results are accurate enough to indicate that the DDI may be a viable option in many more scenarios than previously thought. This study concludes that it is worthwhile for practitioners to consider the DDI for any interchange improvement when comparing it with other diamond interchange forms.

Control Delay Calculation at Diverging Diamond Interchanges

Diverging diamond interchange (DDI) is a form of diamond interchange attracting growing interest from traffic engineers and researchers. Conventional control delay calculation models are not effective when applied to DDI because of the possible internal queue spillback. This paper describes a method to calculate control delay at DDI using a new analytical model. The model was first developed for control delay calculations of external movements at conventional diamond interchanges. Through the addition of a function to calculate delay of internal movements, the model was successfully used at a DDI to calculate control delay of both internal movements and external movements. Simulation studies are also conducted to validate the new model. This study can be used either as a stand-alone delay calculation model or as a supplement to existing simulation methods. The model also shows promise for use in other signalized interchange configurations with two or more adjacent intersections.

Design and Operational Performance of Double Crossover Intersection and Diverging Diamond Interchange

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.

Design and Operational Performance of Double Crossover Intersection and Diverging Diamond Interchange

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.