Crossover Roundabouts

DDI (Diverging Diamond Interchange) as an improved diamond interchange type is getting increasing use across the United States, however, its operational performance and feasibility in China remains unclear. This paper, combined with Chinese traffic conditions, presents operational performance evaluation and feasibility analysis of DDIs. It proposes a mathematical methodology, which could determine the capacity and level of service of DDIs, with critical movement theories. Besides, it compares the network performance of DDIs, improved and conventional diamond interchanges in VISSIM, and analyzes the crash data to obtain the applied condition of DDIs. The results show that the critical movement based evaluation procedure is a quick and reliable method to analyze DDIs in a planning stage, and DDIs are appropriate treatments to replace domestic over-capacity diamond interchanges, especially for locations with high left-turn demands to and from the freeway.

Auxiliary lanes (ALs) provide significant operational benefits by spreading merging or weaving movements over a long distance or by providing an extra lane of capacity through a freeway bottleneck or signalized intersection. However, if ALs are not long enough, they may produce merge bottlenecks and queue spillbacks onto the main lanes of the freeway or arterial, creating operational and safety concerns. While there is literature or guidance for ALs on freeways, there is minimal design guidance for ALs on frontage roads. This study systematically examines various design elements of ALs on frontage roads and the design parameters that influence these design elements by leveraging microsimulation. The key purpose of this study is to develop recommendations for the length of ALs in six common frontage road design configurations based on the selected nine design parameters. More than 3,000 simulation runs were performed to develop and compare guidance with the existing design manuals. The results reveal new insights that would complement existing design guidance.

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.

In some states, frontage roads are frequently used along freeway and fully controlled principal arterial corridors. Their primary function is to provide access between the arterial, or freeway, and adjacent developed property. Little information about the safety performance of rural frontage roads exists. This paper describes the development of a safety performance function (SPF) and accident modification factors (AMFs) for rural frontage road segments. Both one-way and two-way frontage road operations are addressed. The AMFs quantify the relationship between specific changes in geometric design and road safety. The findings from this research show that wider lanes and shoulders are associated with a reduction in segment-related collisions. In addition, the data suggest that the presence of edge marking has an impact on rural two-way frontage road safety. The SPF developed for this research indicates that, for the same traffic volume, rural frontage road segments experience about the same number of severe crashes as typical rural two-lane highways.

Diverging Diamond Interchanges (DDIs) are an innovative form of grade separated interchange which have proven to deliver operational and safety benefits, as well as substantial cost savings in their successful implementation around the world. DDIs provide an opportunity to efficiently upgrade existing grade separated interchanges on the national road network through retrofitting, providing safety and operational benefits which align with evolving policy for sustainable road infrastructure development, and promoting the safe, efficient and sustainable mobility of people and goods in Ireland.

The diverging diamond interchange (DDI) is growing in popularity as an interchange treatment, yet there is rather limited guidance available on signal timing practices. One particular area of concern is the coordination of a DDI along with neighboring intersections in an arterial. This study examines three different cycle length strategies for DDI coordination: (1) using the full cycle length of the corridor; (2) using a half-cycle; and (3) using a previously described three-phase scheme intended to manage queues within the DDI. Six different origin-destination (O-D) scenarios are tested in a microsimulation study. Results are presented in terms of the number of stops, movement delays at the DDI, queue lengths, and delay by O-D path. The outcomes show that the half-cycle strategy yielded lower total and average delays yet resulted in more stops along the arterial and higher arterial O-D path delays. The full-cycle option, meanwhile, tended to achieve fewer stops and lower delays for arterial routes but increased total and average delays for other movements. The three-phase strategy often reduced delays and queue lengths for the arterial movements exiting the DDI, but increased these for other movements.

Deployments of diverging diamond interchange (DDI) have increased in recent years. Most research has focused much effort on optimizing signal timing within the DDI, but there remains a need to optimize a DDI within an existing system to ensure smooth corridor operation. This paper presents a methodology for optimizing offsets on a corridor including a single-controller DDI. This methodology uses high-resolution controller data and an enhancement to the linkpivot algorithm that deconstructs the single-controller parameters into equivalent offset adjustments. The methodology is demonstrated by its application to a 5-intersection arterial route including a DDI, and the outcomes are assessed by measurement of travel times by Bluetooth vehicle re-identification. A user benefit methodology is applied to the travel time data that considers the reliability of the travel times in addition to the central tendency. Further, the methodology is applied to origin-destination (O-D) paths that travel to and from the freeway in addition to routes along the arterial. A total annualized user benefit of approximately $564,000 was achieved. The paper concludes by discussing how the method can also be applied to other nontraditional control schemes connected to arterials, such as continuous-flow intersections and TTI four-phase diamonds.

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.

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.

Even though diverging diamond interchanges (DDIs) have been the subject of research for more than a decade, the effort to standardize interchange signal timing has developed only recently. A three-factor fully crossed experiment was conducted to investigate the influence of crossover spacing and increased volumes on the performance of DDI phasing schemes. PTV Vistro software and the dynamic bandwidth assessment tool were used to optimize the split, cycle length, and offset of each of the 72 treatments. PTV Vissim software was used to collect microsimulation data. Mean interchange delay and mean stops per vehicle were selected as measures of effectiveness. Pairwise comparisons were used to determine whether an existing preferred phasing scheme could minimize delays or stops under three cases: ( a) given spacing and increased volume, ( b) given volume independent of spacing, and ( c) given spacing independent of increased volume. The data revealed that a two- or three-critical-movement phasing scheme usually resulted in the lowest mean interchange delay and the fewest stops. Overall, the results provide an initial signal timing scheme for practitioners given a crossover spacing, an increased volume, or both. Future work will include exploring low volumes, balanced interchange volumes, and their effects on the four-critical-movement phasing scheme, as well as the effect of closely spaced adjacent intersections.

본 연구는 최근 미국에서 그 수가 폭발적으로 증가하고 있는 특이형태 교차로의 하나인 엇갈림 다이아몬드 교차로에 대해 다루었다. 교차로의 기본 특성 및 차량통행 방법을 소개하였고, 교차로의 장단점과 그 수가 기하급수적으로 늘고 있는 사유에 대해 고찰해 봤다. 또한 미국 내 92개의 운영 중이거나 건설 중인 엇갈림 다이아몬드 교차로의 설치위치에 대해서도 분석하였다. 설치위치 분석을 위해 엇갈림 다이아몬드 교차로가 위치하거나 인접한 도시의 인구규모와 도시 중심부까지의 거리를 검토하였다. 다음으로 엇갈림 다이아몬드 교차로의 교통안전 측면도 분석하였다. 특히 7개 교차로에서 수집한 교통상충과 오조작에 대한 카이스퀘어 검정을 통해 발생빈도의 독립성 여부를 확인하였다. 본 연구는 향후 우리나라에서 엇갈림 다이아몬드 교차로 설치를 고려 시 도움이 될 것으로 기대한다.

Crossover effects and molecular mass regions in solutions of worm-like polymers: a new relation for the determination of their statistical segment length, based on the blob model

<p>[[Video(http://www.youtube.com/watch?v=B6d7xeYlAiw)]] This video shows three-phase operations featuring a hold-back phase with data characterizing the southbound internal through movement (OL-C) on May 15, 2014, at the SR-201 / Bangerter DDI in Salt Lake City, Utah. The gray dots are associated with vehicles from the upstream ramp movement (OL-H) and the black dots are associated with vehicles from the upstream external through movement (OL-E). Radar detection was used, so closely spaced vehicles often generate one detection for the group instead of a unique detection for each vehicle. Latitude/Longitude: 40.726568° / -111.9855606°</p>

In this paper we propose a method to evaluate the performance of an intersection using location traces collected from sampled vehicles. The performance is measured in terms of the times the vehicles spend traveling through the intersection. As a use case, we apply the method to conduct a before and after study for 1) two unconventional intersection projects including a continuous flow intersection (CFI) and a diverging diamond interchange (DDI), and 2) for two neighboring conventional intersections to factor out effects due to possible changes in the local traffic volume. The analysis shows that for the CFI project travel time is reduced after construction. On the other hand, we find two unexpected results: 1) for the DDI project, we observe an increase of travel time after construction and 2) for the CFI project, we find a decreased benefit during rush hours. We further translate the time reduction to economic benefit based on traffic volume and value of time to offer an understanding of ROI (Return on Investment) for the intersection modification construction costs.

We propose a panel data-based discrete-continuous modeling framework to analyze driver behavior in two disparatetrajectory datasets – one from a heterogeneous disorderly (HD) traffic streamin India and another from a homogeneous traffic stream in the United States. Thepanel data-based framework allows the analyst to isolate the subject vehicle-and driver-specific unobserved factors that influence driver behavior. Doing sohelps reduce the confounding effects of such unobserved factors on analyzingthe influence of observed factors, such as relative speeds and spacing betweenthe subject vehicle and other vehicles, on driver behavior. The empiricalresults reveal both similarities and differences in driver behavior between thetwo trajectory datasets. In addition, the analysis sheds light on the suitability of different lengthsof influence zones on driver behavior in the two datasets. The insights from this study can help improve driver behavior modelsand traffic simulation frameworks for both traffic conditions..