Diverging Diamond Interchange Research Articles

Evaluating Pedestrian Service of the New Super Diverging Diamond Interchange on Three Case Study Sites in Denver, Colorado

Ensuring safe and comfortable conditions for pedestrians necessitates specific strategies at intersections and service interchanges where traffic and pedestrians interact in complex ways with other modes of transportation. This study aims to investigate pedestrian performance at the new Super Diverging Diamond Interchange (Super DDI) using real-world locations (i.e., I-225 and Mississippi Ave, I-25 and 120th Ave, and I-25 and Hampden Ave in Denver, Colorado). Three alternative designs, typical DDI, and two versions of Super DDI were considered to make a reasonable comparison with the existing Conventional Diamond Interchange (CDI). A comprehensive series of simulation models (192 scenarios with 960 runs) were tested using VISSIM and Synchro to analyze pedestrian operation (travel time, number of stops, and waiting time) in various traffic and pedestrian distributions. As one of the primary contributions in this paper, pedestrian safety was evaluated based on a surrogate performance measure called design flag, introduced by the new National Cooperative Highway Research Program (NCHRP-948) guideline. The results indicated that the proposed new Super DDI designs are relatively safe when compared with CDI and DDI. For example, a pedestrian analysis of one of the most popular alternative interchanges, DDI, showed potential for unsafe pedestrian conditions in all aspects.

Conventional Diamond, Diverging Diamond, and Single Point Diamond Interchanges: A Comparative Operational Performance Evaluation in the Era of Connected Vehicles

This study evaluates the mobility impact of implementing Connected Vehicle (CV) technology at the Conventional Diamond Interchange (CDI), Diverging Diamond Interchange (DDI), and Single Point Diamond Interchange (SPDI). The evaluation is based on a microsimulation environment created in VISSIM combined with ASC/3 Software-in-the-Loop signal controllers and Python-programmed Vehicle to Infrastructure (V2I) communication algorithms. The effect of varying CV-Market Penetration Rates (CV-MPRs) on traffic operations is taken into consideration. The study shows that the interchange design has a higher impact on traffic operations than does the CV-MPR. Particularly, a 100% CV-MPR has led to 6.4% reductions in delays compared to the 0% CV-MPR, without considering the effect of interchange design. Contrarily, the CDI would increase delays as high as 24.0% as opposed to the SPDI, without considering the effect of CVs. Similarly, the DDI would reduce delays by up to 60.6% compared to the SPDI, without considering the effect of CVs.

Concurrent Optimization of Cycle Length, Green Splits, and Offsets for the Diverging Diamond Interchange

Diverging diamond interchange (DDI) has received increased attention from the traffic community for its efficiency in reducing delays for vehicles at on- and off-ramps. The conflicting through movements between a DDI’s two crossover intersections mean that its signal plan must concurrently consider the progression for all critical paths to ensure overall efficiency. In light of DDI’s unique geometric features, the design of its signal plans typically starts with the cycle length and green splits for its two crossover intersections, and then employs available progression models to produce the optimal offsets for those critical paths. Such a two-stage design methodology, however, often cannot yield system-wide optimal results because the optimal progression bandwidth and signal settings are interdependent. Moreover, inefficient coordination between its two crossover intersections may cause excessive queues on the DDI’s bridge segment. This paper therefore presents a mixed-integer linear programming (MILP) model that can concurrently optimize the cycle length, green splits, and offsets for a DDI’s two crossover intersections under the given traffic patterns and geometric constraints such as the link length. The results of extensive numerical analyses with a real-world DDI have confirmed the effectiveness of the proposed model and its robustness in response to demand fluctuation.

Engineering Countermeasures for Left Turns at Signalized Intersections: A Review

Left turn crashes can impact the safety of the drivers due to the speed and angle at which they occur. Left turns are specifically reported to affect older drivers more than the other types of crashes. This paper provides a review of the existing engineering countermeasures that have been evaluated to improve driver safety at left turns. Twentyeight studies on left turn signal displays (protected left turns, flashing yellow arrow, and digital countdown timers), intersection geometry (offset left turn lanes, diverging diamond interchange, roundabouts, exit lanes for left turn, left turn bay extension, and contraflow left turn lanes), and driver warning systems (infrastructure warning systems, and in-vehicle warning systems) are reviewed. Eighteen studies were evaluated in the field, nine in laboratory environments, and one online. All countermeasures demonstrated varying levels of effectiveness. We found protected left turns, roundabouts, and warning systems to be the most effective engineering countermeasures. Advantages and disadvantages of each countermeasure and research shortcomings of the evaluation studies are discussed. Review findings may help practitioners and researchers guide more effective countermeasures for left turns for older drivers.

Surrogate safety assessment of super DDI design: A case study in Denver, Colorado

This paper aims to advance the current research on the new super diverging diamond interchange (Super DDI) design by evaluating the safety performance of its two versions (super DDI-1 and super DDI-2) using real-field data. Three interchanges were selected in Denver metro, Colorado as the potential candidates to model for future retrofit. This study considered four interchange designs (i.e., existing diamond, DDI, super DDI-1, and super DDI-2) to assess the safety performance using the combination of VISSIM, Synchro, and SSAM analyzing tools. Several microsimulation models (120 scenarios with 600 runs in total) were created with three peak hours (AM, Noon, and PM) for existing (the year 2020) and projected (the year 2030) traffic volumes. Based on the results, both super DDI versions showed high potential in improving safety. As an important finding from this research, super DDI designs outperformed DDI when considering adjacent signals, while DDI performed apparently similar or sometimes even insignificantly better compared to super DDI if no adjacent intersections were located in the vicinity and if the demand was lower than DDI’s capacity.

Evaluating the Operational Efficiency of Two Versions of Super Diverging Diamond Interchange Design: A Case Study in Denver, Colorado

This paper aims to advance the current research on the new super diverging diamond interchange (super DDI) design by evaluating the operational efficiency using real-world locations. As part of a comprehensive research effort on improving the performance of failing service interchanges in the mountain-plains region, the study identified three interchanges (Interstate 225 and Mississippi Avenue, Interstate 25 and 120th Avenue, and Interstate 25 and Hampden Avenue) at Denver, Colorado as the potential candidates to model for future retrofit. Four interchange designs (i.e., existing CDI [conventional diamond interchange], DDI, super DDI-1, and super DDI-2) were tested in this study. The operational analysis was conducted using VISSIM and Synchro. Several microsimulation models (120 scenarios with 600 runs in total) were created with three peak hours (a.m., noon, and p.m.) for existing (the year 2020) and projected (the year 2030) traffic volumes. The study considered two simulation networks: (1) when no adjacent traffic signal exists, to determine how the four interchange designs would perform if there were no adjacent signals or they were far away from the interchange; and (2) when there are two adjacent traffic signals, to evaluate the performance of the four interchanges in a bigger corridor with signal coordination needed. An important finding is that super DDI designs outperformed DDI with adjacent signals and higher traffic demand, while DDI performed similarly to or sometimes insignificantly better than super DDI if no adjacent intersections were located in the vicinity and if the demand was lower than the DDI’s capacity.

Evaluating safety performance of the offset diamond interchange design using VISSIM and surrogate safety assessment model

Many existing interchanges, which were built mostly in 1950s and 1960s based on old design guidelines, have operational and/or safety problems due to the inconsistency with current traffic and pedestrian demands. Therefore, upgrading existing designs based on recent policies and demands could result in improving the performance of old interchanges. This research evaluates traffic safety and pedestrian performance of the new offset diamond interchange (ODI) as a substitute for failing conventional interchanges. The ODI design, which showed potential in improving traffic operation in a past study by the authors, was compared to nine interchange designs using VISSIM and the Surrogate Safety Assessment Model (SSAM) in this study to examine the safety and pedestrian performance. Overall, 324 simulation scenarios were tested with various conditions of traffic and pedestrian volumes, turning traffic ratios, traffic distribution, and truck percentages. According to the results, the ODI showed potential to be a promising design in terms of safety and pedestrian performance. However, the diverging diamond interchange (DDI) resulted in fewer simulated conflicts compared to the new ODI. On the other hand, the ODI design had a better performance in terms of pedestrian performance.

Systematic Safety Evaluation of Diverging Diamond Interchanges Based on Nationwide Implementation Data

Diverging diamond interchanges (DDIs) are designed as an alternative to the conventional diamond interchanges to enhance operational and safety performance. As the popularity of the DDI is increasing and more DDIs are being constructed and proposed, the need has arisen to measure the actual safety benefits of DDIs as compared with the traditional diamond interchanges. This study evaluates the safety of DDIs using three methods: before–after study with comparison group, Empirical Bayes before–after method, and cross-sectional analysis. This study collected a nationwide sample of 80 DDIs in 24 states. The estimated crash modification factors indicated that converting conventional diamond interchange to DDIs could significantly decrease the total, fatal-and-injury, rear-end, and angle/left-turn crashes by 14%, 44%, 11%, and 55%, respectively. Moreover, the developed safety performance functions implied that a longer distance between crossovers/ramp terminals and a lower speed limit on freeway exit ramps are significantly associated with lower crash frequency at diamond interchanges. This study contributes to the existing literature using a relatively large representative sample size, which provides more reliable evaluation results. In addition, this study also explored the effects of different traffic and geometric characteristics on the safety performance of DDIs.

Diverging Diamond Interchange Performance Measures Using Connected Vehicle Data

Since the first Diverging Diamond Interchange (DDI) implementation in 2009, most of the performance studies developed for this type of interchange have been based on simulations and historical crash data, with a small number of studies using Automated Traffic Signal Performance Measures (ATSPM). Simulation models require considerable effort to collect volumes and to model actual controller operations. Safety studies based on historical crashes usually require from 3 to 5 years of data collection. ATSPMs rely on sensing equipment. This study describes the use of connected vehicle trajectory data to analyze the performance of a DDI located in the metropolitan area of Fort Wayne, IN. An extension of the Purdue Probe Diagram (PPD) is proposed to assess the levels of delay, progression, and saturation. Further, an additional PPD variation is presented that provides a convenient visualization to qualitatively understand progression patterns and to evaluate queue length for spillback in the critical interior crossover. Over 7000 trajectories and 130,000 GPS points were analyzed between the 7th and the 11th of June 2021 from 5:00 AM to 10:00 PM to estimate the DDI’s arrivals on green, level of service, split failures, and downstream blockage. Although this technique was demonstrated for weekdays, the ubiquity of connected vehicle data makes it very easy to adapt these techniques to analysis during special events, winter storms, and weekends. Furthermore, the methodologies presented in this paper can be applied by any agency wanting to assess the performance of any DDI in their jurisdiction.

Optimized route to clear diverging diamond interchange using discrete optimization method

Interchanges and intersections are the most complex part of a roadway network and are very challenging for snow plowing operators. The objective of the study is to test if the empirical best plowing route to clear a diverging diamond interchange (DDI) recommended by Clear Roads is also mathematically optimized. A discrete optimization method was employed to find the shortest route. In the study, the DDI is represented as a directed graph model. The task of clearing all lanes is treated as the well-known directed Chinese postman problem, which was then solved by an existing network optimization algorithm upon appropriate modification. The results showed that the best practice plowing route recommended by Clear Roads is one of the computed optimal routes with the efficiency index of 2/3. The approach proposed in the study can also be applied to other complex intersections and interchanges and help agencies achieve cost-effective snow control operations.

A fuzzy logic simulation model for controlling an oversaturated diverge diamond interchange and ramp metering system

Traffic congestion is a global problem that cannot be solved by continuing to add new roads and extra capacity, which is accentuated in the areas where roads of unlimited-access (e.g. arterial streets) interface those of limited-access (e.g. freeways). Many researchers have addressed this problem but we present here a novel method to utilize a fuzzy logic model to reduce traffic congestion in such interfacing areas during saturated traffic conditions. More specifically this paper presents a control method for a complex traffic control system: Diverging Diamond Interchange (DDI) - Ramp Metering (RM), under oversaturated traffic conditions. The DDI is a relatively new concept of an alternative intersection geometry where two intersections serve left-turn movements without conflicts. However, such DDI left-turn movements, along with the right-turn movements from the opposite direction, put additional ‘pressure’ on the on-ramp of the freeways or multilane highways that intersect with DDIs. If freeway operations are saturated or near saturation, which may be the result of RM operations, this type of traffic control system can lead to a fully jammed condition with a potential spillback. The purpose of the proposed fuzzy-logic control is to prevent such a queue spillback from the metering ramp to the DDI. After presenting the fuzzy-logic control (FLC) model, we compare it to the conventional fixed time control (FTC) to evaluate potential benefits. To assess the quality of proposed analytical solutions in the real-traffic-like environment we evaluated the two logics in a VISSIM microsimulation model. The results show that, when compared to FTC, the FLC method improves traffic conditions moderately but in the oversaturated environment where there is very little room for improvement.

Comparing the efficiency of the super diverging diamond interchange to other innovative interchanges’

Innovative interchange designs are gaining attention due to their potential in reducing delays and mitigating congestion. This study was aimed at proposing the super diverging diamond interchange (SDDI) as an alternative design to the conventional diamond interchange (CDI), diverging diamond interchange (DDI), diverging partial cloverleaf interchange (DPCI), folded diamond interchange (FDI) and ramp crossover interchange (RCI) designs. An evaluation of the operational performances of the six interchange designs in terms of both vehicular and pedestrian travel times was conducted. The VISSIM micro-simulation software tool was used where several scenarios were proposed and examined. The study was carried out for the E. Mississippi Ave. and I-225 interchange in Aurora, Colorado as part of a project. Note that the interchange, mentioned, is currently operating as a CDI. ANOVA hypothesis tests were conducted to compare the travel times required for both vehicles and pedestrians to navigate each interchange type. The results indicated that, for under-saturated conditions where demand volumes were less than the interchanges’ capacities, implementing either the FDI, SDDI or RCI designs substantially reduced vehicular travel times as opposed to implementing the other designs. On the other hand, for over-saturated conditions in which traffic volumes exceeded capacities, the RCI and FDI exhibited the least vehicular travel times. The CDI was demonstrated to be the most efficient interchange serving pedestrians in all simulated scenarios. It was closely followed by the RCI and SDDI particularly for over-saturated conditions.

Sustainable Design of Diverging Diamond Interchange: Development of Warrants for Improving Operational Performance

Conventional diamond interchanges are facing ever-growing challenges related to traffic operations and safety risks due to increasing traffic volumes and worsening congestions. The agencies are well aware of the high socioeconomic (e.g., user delay cost, fuel cost, and high accident rates) and environmental losses (traffic emissions due to vehicles queuing) associated with the conventional interchange design. This paper provides insight into the different factors that affect the sustainability performance (operational and safety) of a conventional interchange through its redesign into the Diverging Diamond Interchange (DDI) with the increased left-turn demand. It also assesses the need to redesign an interchange to improve the efficiency. Two interchanges that have DDI designs were selected for investigations, and the required data were collected from the relevant agency. The average delay and the capacity were used as the Measures of Effectiveness (MOEs) for data analysis. Numerous factors, that affected these MOEs, were used to design an experiment. This experiment included different levels of volumes, geometric designs, and signal plans. The micro-simulation software (VISSIM 8.0) was employed to calibrate and validate the existing conditions through several steps, including signal optimization and driving behavior parameter optimization. The analysis of the results detected the key thresholds of switching from the conventional design to the innovative design under 90 different scenarios. Finally, the sustainability evaluation of DDI and Conventional Design Interchange was conducted based on their operation and safety performance comparison. The results and findings of this research will act as a guideline for decision-makers regarding when they should consider switching from the conventional interchange design to an innovative design.

Diverging diamond interchanges: A driving simulator study

This study assessed driver performance while navigating a Diverging Diamond Interchange (DDI) compared to a standard intersection in a driving simulator. A total of 201 Western Australian (WA) drivers aged 18–80 years completed the simulator drive and questionnaire. Measures of driving simulator performance assessed included time spent out of lane, number of lane excursions, compliance to the speed limit, crashes and near misses. Other driving measures, which were recorded by the researcher, included driver errors/violations such as red-light violations, wrong way violations and navigation errors. Qualitative information was also obtained in a post exit interview with each participant regarding the difficulties they experienced when driving through the DDI. A repeated-measure analysis of variance (r-ANOVA) was undertaken to examine differences in intersection type (DDI versus standard intersection) and driving performance measures from the driving simulator. The only significant result was compliance to the speed limit (F (1, 656) = 160.11,p < 0.001) on the driving simulator. A higher proportion of red-light violations were observed by the researcher as participants navigated through the DDI, compared to the standard intersection. Qualitative comments from participants also highlighted the need for better signage and road markings. Recommendations when DDIs are implemented include community education on speed limit compliance, avoidance of red-light violations and design improvements regarding signage and road markings.

Improving Traffic Operations at Service Interchanges using the New Offset Diamond Design

This paper proposes the new offset diamond interchange (ODI) as an alternative design which shows potential in mitigating the limitations of failing service interchanges in relation to traffic operation. Vehicle travel time was considered as the primary measure of effectiveness (MOE) for the traffic operation analysis, while the maximum queue lengths were also analyzed. A comprehensive series of VISSIM simulation scenarios was conducted to evaluate the new ODI design in different situations of traffic demand, turning-traffic ratios, traffic distribution, and traffic composition. The results were compared with five existing and four other new interchange designs. The new ODI performed statistically significantly better than all existing designs, including the conventional diamond, parclo A, and the diverging diamond interchange (DDI). The ODI design was found vulnerable in relation to the maximum queue produced in high turning conditions with the unbalanced traffic distribution; however, the threat could be diminished by increasing the storage lengths about 80 ft. Right-of-way (ROW) costs may make the ODI a poor alternative in replacing a standard diamond, but since the ODI fits the footprint of a parclo A it could work well in replacing those interchanges.

Performance Evaluation of Diverging Diamond Interchange Compared to Conventional Diamond Interchange: A Case Study in Riyadh City

The road users usually suffer from several kinds of congestion and delay especially at intersections. The traffic flow congestion due to increasing traffic volumes can be decreased by implementing some suitable alternative designs of interchanges such as Diverging diamond interchange (DDI) and conventional diamond interchange (CDI). In this study, a comparison between the DDI and CDI in traffic conditions in Riyadh city is conducted. The analysis involved different measures of effectiveness that includes delay, queue length, and number of stops. In this context, each interchange type was evaluated for traffic volumes at certain peak hours using micro-simulation program named as “Synchro.” The finding of this study shows that DDI provides a better result when compared with CDI in terms of delay, queue length and number of stops. The control delay for the DDI is approximately one third of the CDI. Also, the queue length for the DDI is about one half of the CDI. Furthermore, the number of stops for the DDI is as one half as the CDI.

Operating Performance of Diverging Diamond Interchanges

As the result of changing traffic patterns, many conventional intersections and interchanges can no longer accommodate growing traffic volumes and heavy turning movements. In response, there are various innovative intersection and interchange designs proposed and implemented to better accommodate these changes, and the diverging diamond interchange (DDI) is one of these alternatives. While there is a significant amount of research on the relative performance of DDIs and conventional diamond interchanges (CDIs), a clear set of guidance on demand conditions under which a DDI is likely an operationally more efficient solution is not readily available. This effort conducts a sensitivity analysis of CDI and DDI operational performance under various interchange lane configurations, including the selected study area of the Jimmy Carter Boulevard and I-85 interchange in Norcross, Georgia, under varying traffic demands and turn-movement ratios. The sensitivity analysis explores the detailed conditions in which one interchange configuration provides superior performance over the other. The sensitivity analysis is structured into a two-step process with a critical lane volume (CLV) analysis as the first step, followed by a VISSIM microscopic simulation study as the second step. Overall, the study found that a CDI is likely to be the preferred option at locations with traffic volumes well below capacity and cross-street left-turn traffic proportions below 30% of the total cross-street demand, and a DDI is likely to be preferred at locations with traffic volumes near capacity and cross-street left-turn proportions exceeding 50% of the total cross-street demand.

National-Level Safety Evaluation of Diverging Diamond Interchanges

A national-level safety evaluation of Diverging Diamond Interchanges (DDIs) in the United States was completed. This study aimed to update previous evaluations and to expand the treatment group size of previous studies to provide a more robust and reliable safety assessment of DDI deployments. For this particular treatment, it was determined that, of the observational before-and-after evaluation methodologies, the comparison group approach yields the best evaluation results. The naïve method can be influenced by outside factors that cannot be accounted for (weather, crash reporting tendencies, etc.). The empirical Bayes method is unnecessary as DDIs are installed for operational benefits, meaning that risk of selection bias and regression-to-the-mean is minimal. This study recommends a total crashes crash modification factor (CMF) of 0.633 based on the comparison group analysis of 26 DDIs in 11 states. The comparison group method was also applied to a variety of crash variables for this study. Angle, rear-end, and sideswipe crashes were found to have CMFs of 0.441, 0.549, and 1.139, respectively. Fatal-and-injury crashes provided a CMF of 0.461. Daytime and nighttime crashes provided CMFs of 0.648 and 0.638, respectively.

Modeling safety performance of the new super DDI design in terms of vehicular traffic and pedestrian

Most existing interchanges in the United States were built more than 50 years ago based on old design policies. Many of these designs are not consistent with current traffic and pedestrian demands anymore. Therefore, this inconsistency has caused problems regarding operation and safety. This paper models safety performance of a new design called super diverging diamond interchange (super DDI) considering VISSIM simulation and surrogate safety assessment model (SSAM). Six other interchange designs were also considered for comparing to the new super DDI design. Overall, 252 simulation scenarios were modeled in VISSIM and then tested by SSAM. Also, the same number of tests were considered to evaluate pedestrian performance of the designs considered in this study. Based on results, super DDI showed a high potential either in terms of traffic safety and pedestrian safety. In comparison to other designs, super DDI had the minimum number of simulated conflicts as well as the lowest mean speed and time to collision (TTC) of simulated conflicts. This fact shows that super DDI could perform promising in reducing crash frequency and crash severity. Reviewing the geometry of the super DDI, lower traffic involving in each conflict point should be one of the main reasons for the promising traffic safety performance of the design. Regarding pedestrian performance, super DDI got the third rank of the lowest mean pedestrian travel times. There is no free-flowing conflict between vehicles and pedestrians in a super DDI. Therefore, pedestrian paths of the super DDI are predicted to be safer than the paths in a typical DDI design.

Introducing the Super DDI as a Promising Alternative Service Interchange

The diverging diamond interchange (DDI) is in widespread use all around the United States and is the most popular alternative design for failing conventional interchanges. While the DDI does well in efficiently moving large left-turn demands, it is not the best design for through traffic or pedestrians. This paper proposes the new super DDI as a substitute for service interchanges which can mitigate the limitations of the typical DDIs. Our study of the new super DDI included a comprehensive series of simulation tests in VISSIM to consider different aspects of the traffic operation. We also estimated the costs of constructing a super DDI and compared those costs to other interchange designs. The results confirmed that the proposed super DDI could perform significantly better than the existing designs under the conditions tested. Overall, the super DDI showed an 18% lower travel time and a 49% higher rate of completed tests (as an indicator of the capacity) when compared with a typical DDI. However, the construction cost was estimated to be higher. Hopefully, the results show that the proposed super DDI has potential as a promising alternative design and will inspire further research and testing.