Intersection Design Research Articles

Safe System for Intersections Method Scoring: Comparing Intersection Alternatives Based on Exposure, Kinetic Energy Management, and Movement Complexity

Transportation agencies across the U.S. are increasingly looking to the Safe System approach as a path toward achieving Vision Zero and other similar road safety performance goals. Vision Zero and the Safe System approach seek to eliminate traffic fatalities and serious injuries. The Federal Highway Administration (FHWA) funded an effort to create a Safe System for Intersections (SSI) method to provide a technical basis by which road planners and designers could apply Safe System principles on intersection projects, detailed in the report A Safe System-Based Framework and Analytical Methodology for Assessing Intersections. Applying the SSI method results in a set of SSI scores for each intersection design under consideration. The SSI scores characterize the extent to which an intersection alternative aligns with Safe System principles. This paper builds on the content presented in the FHWA report and describes how the key SSI method components of user exposure, conflict point severity, and intersection movement complexity are combined to produce the SSI scores. This additional background and detail on the development of the SSI scores will support future applications of the method and the identification of future research needs and method improvements.

Microscopic Traffic Modeling Inside Intersections: Interactions Between Drivers

Microscopic traffic flow models enable predictions of traffic operations, which allows traffic engineers to assess the efficiency and safety effects of roadway designs. Modeling vehicle trajectories inside intersections is challenging because there is an infinite number of possible paths in a two-dimensional space, and drivers can simultaneously adapt their speeds as well. To date, human driver models for simultaneous longitudinal and lateral vehicle control based on the infrastructure characteristics and interactions with other drivers inside an intersection are still lacking. The contribution of this paper is threefold. First, it proposes an integrated microscopic traffic flow model to describe human-driven vehicle maneuvers under interactions. Drivers plan their heading and acceleration in the predicted future to minimize costs representing undesirable situations. The model works with a joint optimization for an interaction cost term. The weights associated with the interaction cost reflect how selfish or altruistic drivers are. Second, the proposed model endogenously gives the order of vehicles in case of crossing paths. Third, the paper develops a clustered validation method for microscopic traffic flow models with interacting vehicles, which account for interdriver variations. Results show that the model can accurately describe vehicle passing orders of interacting maneuvers, paths, and speeds against empirical data. The model can be applied to assess various intersection designs. Funding: This work was supported by the National Natural Science Foundation of China [Grants 71971140 and 52122215] and the Natural Science Foundation of Shanghai [Grant 20ZR1439300].

Large-Eddy Simulation of Airflow and Pollutant Dispersion in a Model Street Canyon Intersection of Dhaka City

The atmospheric flow and dispersion of traffic exhaust were numerically studied in this work while considering a model street canyon intersection of a city. The finite volume method (FVM)-based large-eddy simulation (LES) technique in line with ANSYS Fluent have been used for flow and pollutant dispersion modelling through the consideration of the atmospheric boundary layer (ABL). Hexahedral elements are considered for computational domain discretization in order to numerically solve problems using FVM-LES. The turbulence parameters were superimposed through a spectral synthesizer in the existing LES model through ANSYS Fluent as part of ’damage control’ due to the unsteady k−ϵ simulation. Initially, the code is validated with an experimental study of an urban street canyon where the width and height ratio is in unity. After validation, a model urban street canyon intersection was investigated in this work. The model shows a high pollutant concentration in the intersecting corner areas of the buildings. Additionally, the study of this model intersection shows a high level of pollutant concentration at the leeward wall of downwind building in the case of increased height of an upwind building. Most importantly, it was realized from the street intersection design that three-dimensional interconnection between the dominating canyon vortices and roof level flow plays a pivotal role in pollutant concentration level on the windward walls. The three-dimensional extent of corner eddies and their interconnections with dominating vortices were found to be extremely important as they facilitate enhanced ventilation. Corner eddies only form for the streets towards the freeway and not for the streets towards the intersection. The results and key findings of this work offer qualitative and quantitative data for the estimation, planning, and implementation of exposure mitigation in an urban environment.

Evaluation of Driving Behavior and Traffic Safety at a Shifting Movements Intersection

Unconventional intersection designs have been proposed for their theoretical potential to enhance traffic safety and operation simultaneously as a result of reducing the number of conflict points and signal phases. However, this has only been achieved with a very limited range of intersection designs which have a very low number of conflict points and under certain traffic conditions. For example, restricted crossing U-turn (RCUT) intersection, which has the lowest number of conflict points among other proposed intersection designs, has operational advantages at extremely unbalanced traffic volumes. Shifting movements (SM) intersection design, which has the same number of conflict points as the RCUT intersection, has been proposed to replace the RCUT implementation at intersections with medium to high minor traffic volumes. It was proven that SM outperforms an RCUT intersection which has medium to high minor traffic volumes in average delay and throughputs. This study aimed to investigate the safety aspects of this intersection design by utilizing the driving simulator. The effectiveness of using infrastructure-to-vehicle (I2V) communication for mitigating confusion at unconventional intersections was also investigated in the study. The results indicated that RCUT and SM intersections have similar safety performance and crossing them is completed with less risk than crossing the conventional intersection. However, there is a need to improve drivers’ knowledge about the SM intersection, especially with regard to the major left-turn movement. Most participants found that using I2V communication was helpful in understanding unconventional movement patterns.

Research on Traffic Design of Urban Vital Streets

As an important part of urban public spaces, the urban street is an important place for people’s lives, communication, and activities. Its vitality directly affects the vitality of the whole city. It is of great practical significance to examine the current situation and theoretical development of urban streets in China and reconstruct the vitality of streets from the perspective of the traffic users. Based on the “people-oriented” design concept of street traffic, this study took street sections and intersections as the main research object, proposed an overall layout of traffic, space, and facilities. A complete set of humanized and green traffic design methods was constructed to enhance the street vitality. First, through the analysis of the concept of road and street, the traffic connotations of the vital street was determined, the characteristics of the vital street was investigated, and the constituent elements of the vital street was summarized. Then, with a focus on people’s needs, the vital street traffic design methods were mainly divided into two parts: vital street section traffic design and vital street intersection design. Finally, Zhongshan Avenue in Wuhan City was chosen for empirical analysis. Through a field questionnaire survey, the traffic characteristics and traffic demands of residents on Zhongshan Avenue were analyzed, and the traffic design of Zhongshan Avenue was carried out in combination with the traffic design method proposed in this study. The results showed that people’s satisfaction with the renovated Zhongshan Avenue reached 90%. Buses, subways, bicycles, and walkways have become the four major green transportation modes for people to arrive at and leave Zhongshan Avenue, and the renovated Zhongshan Avenue has become a vibrant living street.

Photovoltaic Roundabouts for Enhancement of Self-Sufficiency and Resiliency

Roundabouts have become a common type of intersection design in many countries. The area of the center island can be used to install a photovoltaic system to power local loads such as lighting systems. The objective of this study is to evaluate the degree of self-sufficiency that a roundabout can achieve depending on the availability of the area for the installation of a photovoltaic system and the energy demand for lighting. The methodology is divided into five steps aimed at calculating the parameters required to characterize the roundabouts from the point of view of the electricity that can be generated by the photovoltaic systems installed, and then to evaluate the energy consumption required to operate the different system solutions for lighting. The mini roundabouts are not considered as a location for the photovoltaic system; in fact, the minimum diameter must be between 29 and 34 m. Considering the available irradiance in Italy, systems with monocrystalline silicon modules are sufficient to ensure energy self-sufficiency at diameters of 24 m or more. Systems with polycrystalline silicon modules are suitable to ensure energy self-sufficiency at diameters of 25/26 m or more. Photovoltaic (PV) technology continues to make progress in increasing efficiency, such as bifacial PV modules. This means that even smaller roundabouts could be eligible for a PV system sized to meet local electricity needs.

Safety Performance of Unsignalized Median U-Turn Intersections

Alternative intersection designs can offer safety and operational benefits with potentially lower costs than conventional intersections when implemented in the proper setting. The Federal Highway Administration has previously identified a subset of alternative designs called reduced left-turn conflict intersections as a proven safety countermeasure. Median U-turn intersections (also known as “Michigan lefts” or “boulevard turnarounds”) are one such design that accommodates all left-turn movements via directional U-turn crossovers within the median. Prior work has consistently shown that median U-turn intersections can provide superior safety performance when used in the appropriate conditions. However, research that is specific to unsignalized reduced left-turn conflict intersections continues to be limited to work conducted before the Highway Safety Manual, or which includes restricted crossing U-turn intersections. This study included the evaluation of historical traffic crashes and volume data at 95 unsignalized intersections in the state of Michigan. This included the collection of data for 39 median U-turn sites and 56 reference group sites to estimate safety performance functions and crash modification factors that can be used when considering future conversions. Ultimately, crash modification factors for fatal and injury crashes of 0.438 and 0.686 are recommended when converting intersections with undivided two-lane two-way major approaches and four-lane divided boulevard major approaches, respectively. Although there was no significant difference in property damage only crashes associated with converting intersections with undivided, two-lane, two-way major approaches, a crash modification factor of 1.325 is recommended for property damage only crashes specific to conversions with four-lane, divided boulevard major approaches.

Analyzing driver's response to the yellow onset at signalized intersections

Intersections are critical points within the highway system at which the risk of crashes increases. This study seeks to better understand drivers’ behavior at an intersection by examining the relationship between their observed driving behavior, psychological attributes and decision to proceed through an intersection. A driving simulator and self-report questionnaire were used to understand driver decision-making at the onset of the yellow phase across several signalized intersections. The simulator measured driving outcomes such as speed, braking, and throttle as drivers cross through four increasingly difficult intersections. The questionnaires measured demographics, psychological traits including mindfulness and impulsiveness along with self-reported driving behaviors. A total of 102 participants completed the questionnaire as well as the driving simulator experiment. Hierarchical clustering served to classify drivers into four groups on the basis of their observed driving in the simulator: the safest drivers, safe drivers, speed demons, and aggressive drivers. These driving styles moderated the relationship between the drivers’ psychological traits and their decision to stop or proceed at each intersection. Results showed that mindfulness was highly related to the safest drivers’ decision to stop at the first intersection, while impulsiveness and anxiety were related to the speed demons’ decision to stop at the third intersection. These findings lay a strong foundation for developing progressive educational campaigns incorporating driver psychology in their methodology. Findings also provide support for research linking driving performance and psychological traits with implications for intersection design.

Platooning-based trajectory planning of connected and autonomous vehicles at superstreets

ABSTRACT Alternative intersection designs are popular existing strategies that can be used for handling heavy traffic in the U.S., and research on the performance of CAVs in the alternative intersection design can complement our knowledge of the impact of CAVs. Hence, this research attempts to mitigate this research gap through a simulation-based study on a superstreet, one of the popular alternative intersection designs. A real-world superstreet is selected for the simulation-based study with collected traffic volumes and average speeds. HDVs are modeled using Wiedemann 99 with calibrated parameters while CAVs are modeled using the intelligent driver model (IDM). Platooning and trajectory planning capabilities of CAVs are modeled in the designed simulation. The simulation results show that the proposed framework for CAVs can successfully reduce fuel consumption in different market penetration rates and traffic scales.

Modification in Hcm Delay Model for Roundabout for Mixed Traffic Conditions - a Pilot Study

Roundabouts have proven to be an effective intersection design method for smooth traffic flow movements and improved safety. Previous studies show that VISSIM, commercial traffic simulation software, can be used as a proficient tool for modeling and efficiently analyzing roundabouts. This paper focuses on developing a methodology for modeling roundabouts in India using VISSIM. Three typical roundabouts were chosen from the northern part of India. Calibration and validation of the model were performed to ensure the correctness of the model. The average delay and volume to capacity ratio (v/c ratio) were compared for developing the level of service (LOS) thresholds for Indian conditions. The thresholds are compared with existing guidelines provided by the HCM 2010 and AUSTROADS. In addition, the methodology for determining modification factors for applying HCM 2010 delay model in Indian traffic conditions is defined.

Operational design domain of automated vehicles for crossing maneuvers at two-way stop-controlled intersections

The departure sight triangle provides the view for the vehicle waiting to cross at the two-way stop-controlled intersection. The factors influencing the sight triangle for human drivers are considered in the 2018 AASHTO Green Book, but the Green Book lacks quantitative estimations for automated vehicles (AVs). Therefore, to guarantee the AV’s operational safety, this study investigated the impact of intersection angle, speed, and crossing distance on the AV’s intersection crossing maneuver. Using physics theorems and cosine law, formulae for the detecting angle (DA) and distance (DD), the two main components of the departure sight triangle, were developed for the acute- and obtuse-angle sides of the intersection for an AV approaching on the minor road; the minimum required DA and DD, with a given crossing distance, are thus proposed for the AV’s operational design domain (ODD). Calculations indicate that the DD is mainly affected by the major road design speed and crossing distance, and that the DD increases very quickly as the speed and crossing distance increase. The intersection angle was found to have great impact on the DA on both the acute and obtuse sides, but its influence is negative on the acute side and positive on the obtuse side. On the acute side, the ODD detecting angle range is set as [83.4, 132.7], [80.7, 131.6], and [78.4, 130.7] degrees for major roads with 2, 4, and 6 lanes, respectively. On the obtuse side, the ODD is set as [57.4, 160.6], [70.6, 207.9], and [82.2, 249.1] m for the same respective roads. After comparing the DA and DD results, and depending on the intersection design attributes, it is concluded that most engineering attention should be paid to the DA on the acute side and DD on the obtuse side.

A Framework for Estimating Future Traffic Operation and Safety Performance of Restricted Crossing U-Turn (RCUT) Intersections

Background: Despite numerous studies demonstrating the effectiveness of Restricted Crossing U-Turn (RCUT) intersection design, its implementation remains uneven and close to zero in some large states, including California. This paper provides a comprehensive framework to estimate the operational and safety performance of future RCUT designs. The framework is demonstrated for a geometrically constrained intersection located on a high-speed rural expressway. The operational evaluation relies on microscopic simulation models of existing TWSC and alternate RCUT designs used to estimate network-wide performance measures. Methods: Two approaches are demonstrated for future safety estimation; first, an HSM-prescribed Empirical Bayes (EB) approach that uses Safety Performance Function (SPF) predictions combined with the crash history of the site. For typical applications, EB estimates may be combined with CMFs for RCUT found in the literature. This approach remains the preferred option for safety estimation. However, for geometrically constrained locations where atypical RCUT designs need to be evaluated, a surrogate measure-based approach that uses trajectory data from the simulation model is described. Results: Surrogate measure-based safety analysis revelated that the RCUT design with no-left turn from mainline would be the most appropriate design for this location. Conclusion: The framework demonstrated here may be used by agencies to estimate the future benefits of the first-time application of treatments that have been successful elsewhere.

Operational and Safety Performance Evaluation of Parallel Flow Intersection

Unconventional arterial intersection designs have recently gained popularity as an alternative solution to alleviate congestion and mitigate safety problems of at-grade signalized intersections. This study investigates the operational and safety performance of the parallel flow intersection (PFI) under different balanced and unbalanced traffic volume conditions in comparison with a conventional counterpart using VISSIM microsimulation and Surrogate Safety Assessment Model software. The operational performance of the two intersections was based on the overall intersection capacity and the average vehicle delay. The safety performance, on the other hand, was based on the number and severity of simulated conflicts. The results showed that the PFI had a higher capacity compared with the conventional intersection under balanced volume conditions. Under unbalanced volume levels, the PFI outperformed the conventional intersection especially with an increase of left-turn volumes. Moreover, the PFI enhanced the safety conditions relative to the conventional intersection by eliminating all the crossing conflicts under all balanced and unbalanced volume levels and reducing the total number and severity of conflicts at all volume conditions. The study provides guidelines for the optimal spacing distance between the main and secondary intersections for the implementation of the PFI based on its safety and operational impacts on the intersection.

A Nearly Throughput-Maximum Knotted Intersection Design and Control for Connected and Automated Vehicles

A Nearly Throughput-Maximum Knotted Intersection Design and Control for Connected and Automated Vehicles

Signalized Intersection Control in Mixed Autonomous and Regular Vehicles Traffic Environment—A Critical Review Focusing on Future Control

The recent advancement in industrial technology has offered new opportunities to overcome different problems of stochastic driving behavior of humans through effective implementation of autonomous vehicles (AVs). Optimum utilization of driving behavior and advanced capabilities of the AVs has enabled researchers to propose autonomous cooperative-based methods for signalized intersection control under an AV traffic environment. In the future, AVs will share road networks with regular vehicles (RVs), representing a dynamic mixed traffic environment of two groups of vehicles with different characteristics. Without compromising the safety and level of service, traffic operation and control of such a complex environment is a challenging task. The current study includes a comprehensive review focused on the signalized intersection control methods under a mixed traffic environment. The different proposed methods in the literature are based on certain assumptions, requirements, and constraints mainly associated with traffic composition, connectivity, road infrastructures, intersection, and functional network design. Therefore, these methods should be evaluated with appropriate consideration of the underlying assumptions and limitations. This study concludes that the application of adaptive traffic signal control can effectively optimize traffic signal plans for variations of AV traffic environments. However, artificial intelligence approaches primarily focusing on reinforcement learning should be considered to better utilization of the improved AV characteristics.

Modification of Major Intersections in Urban Area of Sialkot City, Pakistan

Traffic management is a major problem in large cities of Pakistan. Pakistan is a developing country with aging infrastructure of roadways and railways. The traffic conditions are deteriorating due to inappropriate design. Traffic problems due to improper design have resulted in loss of the life and property. The main purpose of this study is to identify the existing traffic condition of Sialkot City, Pakistan at Daska, Model Town Bhed Puli and Gulistan Cinema intersection. The Sialkot City is connected with Narowal, Gujrat and Gujranwala through Metalled streets. Sixteen hours of Manual Traffic Count was conducted at each intersection. Equivalent factors for Passenger Car Unit recommended by Government of Punjab are used. Afterwards, analysis has been carried out using Signalized and unsignalized Intersection Design and Research Aid (SIDRA) software. It is observed that Level of Service (LOS) is poor and Volume Capacity Ratio (V/C) is higher for the selected intersections. In order to eliminate the issues of the selected intersection, a few enhancements are suggested and are described in detail. LOS is improved by provision of signals for Gulistan Cinema intersection and Model Town Bhed Puli intersection along with separation of slow moving vehicles by providing service lane; whereas for Daska intersection, freeway provided for traffic channelization with provision of bus bay and parking lane.

Simulation optimisation of displaced left-turn intersection layout with multi-objectives

Displaced left-turn (DLT) intersections, which effectively solve the conflict between left-turn and opposing-through traffic, are currently the most efficient innovative intersection design. However, the special layout of DLT will inevitably cause high difficulty in channelisation design. For full use of the potential traffic capacity of DLT intersection, a multi-objective optimisation model for intersection with DLT layout (MOOM-DLTL) is built based on integrated simulation and mathematical programming (ISMP) framework. In this model, the signal scheme is regarded as the accompanying strategy of DLT layout optimisation to describe the interaction between layout and signal control. In addition, the multi-objective particle swarm optimisation based on shift-based density estimation (MOPSO+SDE) algorithm is developed to obtain the Pareto front of the proposed model. A series of experimental results show that the proposed optimisation method is successful in improving the traffic efficiency of DLT intersection.

Unconventional Intersection Designs for Improving Traffic Operation Along Arterial Roads

The main objective of this paper is to evaluate the effect of implementing four Unconventional Arterial Intersection Designs (UAIDs) including median U-Turn, Superstreet, Jughandle and Single Quadrant Intersection on a major arterial road using SYNCHRO microscopic simulation software. For this purpose, Wadi Saqra Signalized Intersection on Shaker Bin Zaid major arterial road in Amman, Jordan was selected. The simulation results showed that only the Jughandle improved the intersection Level of Service (LOS) slightly, F–E. Nevertheless, the intersection delay was significantly reduced by 64.81%, 76.6%, 91.28% and 75.60% on the proposed Median U-Turn, Superstreet, Jughandle and Single Quadrant unconventional intersection design, respectively. This indicated that these UAIDs don't perform well under heavy traffic volumes. Also, since the Jughandle was the only UAID which improved the LOS on the main intersection, the operational performance of Prince Shaker Bin Zaid arterial after implementing the Jughandle at the main intersection was evaluated including the main intersection: Wadi Saqra intersection, one prior to the main intersection and one after the main intersection. It was found that the use of the Jughandle increased the average travel speed by 35% and decreased the average stopped delay by 28.68% on the arterial road. Also, this paper evaluated the current transportation system and road user's attitude towards UAIDs' implementation through a questionnaire survey. The results indicated high acceptance of UAIDs. Finally, the construction cost for each UAID type was estimated. It was found that the Jughandle had the highest construction cost due to its high acquisition cost.

Implementation of a Double Continuous Flow Intersection in Riyadh

The continuous growth of population in the capital, coupled with increased auto ownership and dependence has worsened traffic conditions on Riyadh's road network. Conventional methods to address this increased demand could be costly and insufficient. There has been greater interest in using alternative measures to improve the performance and safety characteristics on main corridors, particularly those that arrive at signalized intersections. Heavy left turning traffic at these intersections is one of the main causes for delays. Previous research has investigated several types of alternative designs termed "unconventional" arterial intersection designs that could minimize the effect of left turning traffic. This paper provides decision makers with an objective assessment on the efficiency of implementing an unconventional intersection design, the Double Continuous Flow Intersection (DCFI) configuration, to improve the operational and safety characteristics of an existing major signalized arterial intersection in Saudi Arabia. In this study, the Kingdom Hospital Intersection in Riyadh was selected, as it is one of the most congested intersections in Riyadh. Using the collected traffic data, the micro-simulation program VISSIM was used to analyze and compare the efficiency of both configurations. When compared to the existing conventional signalized intersection design, it was found that the proposed Double Continuous Flow Intersection (DCFI) unconventional intersection design decreased the average delay per vehicle by 99 seconds. The proposed Double Continuous Flow Intersection configuration also improved the Level of Service at the intersection from level F (152 sec/veh average delay) to level D (53 sec/veh average delay).

Comparative Study of Operational Performance between Roundabout and Signalized Intersection Using Sidra Software: A Case Study of Addis Ababa City

Abstract: Traffic signals and roundabouts controls are commonly used in several at-grade junctions in urban areas for maximizing traffic efficiency and safety by separating traffic movements in time. The intersection performance is measured by comparing the parameters like- capacity, degree of saturation, delay, queue length, fuel consumption, operating costs and emission, etc. This research paper provides a comparative study of operational performance between a roundabout and signalized intersection at Gergi-Imperial. The traffic data on all approach of the intersection were collected by video camera during the most congested days of the week. The traffic volume obtained in different classes of a vehicle was converted to uniform vehicle fleet by the passenger car equivalency factor. The geometric data for the selected intersections were measured manually. Data analysis and processing were performed using SIDRA (Signalized and Unsignalized intersection Design and Research Aid) intersection software to compare the traffic flow condition at the intersection. The performance measures such as Average delay, Degree of saturation and Level of service at each intersection were interpreted for comparison. The capacities of the signalized intersection were found to be higher than the capacities of roundabout. Signalized intersection was found to be better than the roundabout in terms of the degree of operational performance. Keywords: Average delay, Intersection Capacity, SIDRA Software, Level of Service (LOS), roundabout, Signalized Intersection, Degree of Saturation