Two-way Stop-controlled Intersections Research Articles

Calibration and development of safety performance functions for two-way stop-control intersections on rural two-lane highways in Louisiana

The first edition of the Highway Safety Manual (HSM) contains a simplistic version of the crash prediction model for two-way stop-controlled intersections (TWSC) on rural two-lane highways. This model considers AADT on major and minor roads, with the base conditions defined as no intersection skewness, no turning lanes, and no lighting. A crash modification factor (CMF) will be applied if an intersection has conditions different from the base condition. However, the HSM model does not take account of curvature. It is well known that curved TWSC intersections are less safe than non-curved ones, particularly on rural two-lane roadways. This paper presents the development of crash prediction models incorporating intersection geometrics for TWSC intersections on rural two-lane highways in Louisiana. Then, it compares the results from the developed model with the calibrated HSM model. The negative binomial model was used with 5126 TWSC intersections verified one by one, including both three- and four-leg intersections from all parishes (counties). The estimation results indicate that AADT, curve radius, and intersection skewness angle significantly impact expected crash frequency for both three- and four-leg intersections. This research utilizes cumulative residual plots, mean absolute error, and root mean square error for comparative analysis of HSM models, HSM models with calibration, and Louisiana-specific models. The results show that Louisiana-specific SPFs outperformed the calibrated SPFs with superior reliability. Calibration factors of 0.58 for three-leg intersections and 0.46 for four-leg intersections are estimated, suggesting that the original HSM model overpredicts crashes in Louisiana.

Risk-Taking Driving Behavior in Interacting With an Autonomous Vehicle at Two-Way Stop-Controlled Intersections

During the initial stages of autonomous vehicles (AVs), they will coexist and interact with human-driven vehicles (HVs). There is a research gap in exploring AVs’ impact on human drivers’ risk-taking driving behaviors during such interactions. A questionnaire survey was conducted among 676 drivers to gain insight into this impact. Respondents were asked to complete the questionnaires after understanding the scenarios of interacting between HVs and AVs at two-way stop-controlled intersections. The results demonstrate that human drivers have higher risky driving intentions and perceive lesser social pressure and safety risks when interacting with AVs compared to HVs interactions. Attitudes are the most important factor in explaining risk-taking driving intentions. Furthermore, intentions are directly influenced by perceived behavioral control when interacting with AVs. These findings indicate that human drivers may engage in risky behaviors when interacting with AVs.

Operational Performance of Roundabouts at High-Speed and Rural Locations

A recent research project investigated the operational benefits of modern roundabouts for high-speed locations that serve heavy vehicles, while developing examples of best practices for design. The research team compiled proven results from designs in other states and collected and analyzed data from within and outside of Texas to develop updated design guidance, which can be used to implement roundabout designs that accommodate oversize/overweight (OSOW) vehicles in rural areas. This paper summarizes activities and findings from that project. Project activities indicate that the drone-based data collection effort, along with a computer algorithm-based method for data reduction, was an effective and efficient alternative to traditional data collection and reduction methods for this project. Findings from field data and simulation confirmed practices in other states that roundabouts can be designed to accommodate not only heavy vehicles but also OSOW vehicles in rural locations with high-speed approaches. The roundabout with the largest diameter studied (180 ft) had the best performance, but the smallest roundabout (120-ft diameter) was also able to accommodate larger vehicles at lower volumes, and roundabouts of all sizes generally outperformed two-way stop-controlled intersections in simulation results.

Performance and safety effectiveness evaluation of mini-roundabouts in Michigan

This study evaluates the performance and safety effectiveness of mini-roundabouts. Crash, operational, and geometric data for 14 mini-roundabouts located in the state of Michigan were collected for both before and after installation time periods between 2007 and 2016. Three years of complete before and after installation crash data were analyzed utilizing the Before-and-After study with Comparison Group methodology. A total 28 untreated sites with similar characteristics to the 14 mini-roundabouts sites were used to account for changes in crashes unrelated to the treatment (mini-roundabout installation), evaluate the impacts of the treatment on the intersection, and develop the crash modification factors (CMFs). The results for overall safety effectiveness indicate a decrease in total crashes at signalized intersections when converted into mini-roundabouts, and an increase in total crashes at two-way stop-controlled (TWSC) and all-way stop-controlled (AWSC) intersections when converted into mini-roundabouts. The recommended CMFs for converting a TWSC, AWSC, and signalized intersection into a mini-roundabout are 1.039, 1.051, and 0.755 for total crashes, respectively.

Factors Affecting Driver Yielding at Uncontrolled Crosswalks

This study evaluated driver yielding behavior at basic- versus high-visibility crosswalk (HVC) markings on undivided major street approach legs of two-way stop-controlled intersections. The research team measured and compared driver yielding rates using staged pedestrian crossings at sites with HVCs and at sites with basic markings. Study sites were undivided two-lane roadways with relatively low speeds (25 to 35 mph speed limits) and volumes (up to 616 two-way vehicles per hour during crossings)—half with basic crosswalk markings, half with HVCs. In addition to site characteristic data (crossing distance, presence of bike lane, presence of on-street parking, location context), the study included the collection of vehicle volumes and approach speeds, which enabled statistical modeling of yielding in relation to site characteristics and driver speeds. In total, the study collected 1,188 individual observations at 32 sites in four states. The results showed that, under certain conditions, HVCs were associated with increased driver yielding relative to crossings with basic markings. The study further showed that an approaching driver’s speed and prevailing site speeds had a strong and consistent negative effect on driver yielding. Site context and other treatments present at the site had an impact, but the relationship between driver speed and yielding was robust and statistically significant across all tests. Drivers exceeding 40 mph were unlikely to yield to a pedestrian waiting at a marked crosswalk, suggesting that an agency should consider supplemental treatments to increase driver yielding at such locations.

Modeling the performance of restricted crossing U-turn intersections including the effects of connected and autonomous vehicles: a case study in California

Despite numerous studies demonstrating the effectiveness of restricted crossing U-turn (RCUT) intersection design, its implementation remains close to zero in some large states (e.g., California). The study included four locations on high-speed rural expressways (highways with partial access control) in California. The operational evaluation relies on microscopic simulation models of existing two-way stop-controlled (TWSC) intersections and alternate RCUT designs used to estimate network-wide performance measures. Two series of simulation scenarios were tested: (1) scenarios with no connected and autonomous vehicles (CAVs) and (2) scenarios with different SAE International Level 4 CAV market penetration rates (MPRs) to help policymakers and practitioners in future planning strategies. The microsimulation models were also used to generate trajectory data to create a surrogate measure-based approach. Based on the results, the RCUT designs reduced or eliminated the more severe crossing conflicts. Similar vehicle travel times were identified in various CAV MPRs except for one of the locations with challenging geometric features, where travel time increased at higher CAV MPRs.

Developing Highway Capacity Manual Capacity Adjustment Factors for Connected and Automated Traffic at Two-Way Stop-Controlled Intersections

Connected and automated vehicles (CAVs) hold great promise in enhancing transportation operations and roadway capacity. However, there is still limited guidance in the field of highway capacity analysis to help agencies account for the potential benefits. This paper investigates the impact of CAVs on the capacity of two-way-stop-controlled (TWSC) intersections and quantifies capacity adjustments under different CAV scenarios. An isolated TWSC intersection is considered in this research to analyze the CAV impacts on various intersection movement capacities under different CAV market penetration rates (MPRs) and conflict flow rates (CFRs). To model CAVs, cooperative adaptive cruise control (CACC) is considered because it directly impacts the vehicle’s longitudinal car-following behavior and therefore the capacity. Additionally, enhanced gap-acceptance behavior based on vehicle-to-vehicle (V2V) communication is included because it can benefit minor road movements via advanced notifications. This paper collects data from customized, well-calibrated TWSC simulation models constructed in commercially available software. The results show that with the increase in MPRs, CAVs can substantially enhance the capacity of the stop or yield controlled movements, and the improvement is more significant under low CFR scenarios. CAVs can also reduce the follow-up headway and thus improve the potential capacity based on the existing HCM TWSC capacity estimation method. Finally, based on the data collected from the simulation, a capacity adjustment factor (CAF) table is proposed for HCM implementation.

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.

Safety evaluation of unsignalized and signalized restricted crossing U-turn (RCUT) intersections in rural and suburban areas based on prior control type

The focus of this paper is on evaluating the safety effectiveness of restricted crossing U-turn (RCUT) intersections in rural and suburban areas based on prior control type. Both, unsignalized and signalized RCUT intersections were evaluated using the Empirical Bayes (EB) before-after evaluation method. The 42 RCUT intersections selected for this research were converted from a two-way stop-controlled (TWSC) intersection or signalized intersection in the rural and suburban areas. The results show a 70.63% reduction in the total number of crashes and a 76.10% reduction in the number of fatal and injury crashes at unsignalized stop-controlled RCUT intersections in the rural area. Also, an 89.25% reduction in the total number of crashes and a 94.42% reduction in the number of fatal and injury crashes was observed at offset three-legged unsignalized stop-controlled RCUT intersections converted from four-legged TWSC intersections in rural areas. In the suburban areas, a 64.86% reduction in the total number of crashes and a 73.39% reduction in the number of fatal and injury crashes was observed at unsignalized stop-controlled RCUT intersections. Further, a 10.15% and a 31.08% reduction in the total number of crashes, and an 84.26% and 41.31% reduction in the number of fatal and injury crashes was observed at a signalized RCUT intersection in the rural and suburban areas, respectively. The safety effectiveness of unsignalized RCUT intersections in the rural areas with a larger sample size was found to be higher than was observed by researchers in the past. While unsignalized RCUT intersections in the suburban areas are effective, there is not enough evidence to support the installation of signalized RCUT intersections. These findings help researchers and practitioners in making informed decisions and installing RCUT intersections from a safety perspective.

Evaluation of the efficacy of an intersection conflict warning system at two-way stop-controlled rural intersections: difference-in-differences and triple-difference analytical approaches

ObjectiveIntersection conflict warning systems (ICWSs) have been implemented at high-risk two-way stop-controlled intersections to prevent right-angle crashes and associated injuries. This study involved investigation of the impacts of ICWSs on...

Revised Method for Calculating Departure Sight Distance at Two-Way Stop-Controlled (TWSC) Intersections

This paper introduces realistic acceleration profiles for light-duty vehicles departing from rest at two-way stop-controlled (TWSC) intersections where minor roads (controlled by stop signs) intersect with uncontrolled major roads. The new profiles are based on current vehicle characteristics and driver behavior patterns. They are established based on actual field data collected using global positioning system data loggers that recorded the positional and speed data of various experimental vehicles starting from rest at TWSC intersections. Acceleration profiles are established in this paper and are used to develop a revised method for calculating the departure sight distance at TWSC intersections. Design tables were created to provide realistic sight distance values at TWSC intersections for different design speeds and number of lanes on the major road. It was found that the current values of intersection sight distance suggested by the design guides may be inadequate. Such values may force some approaching drivers on the major road to reduce their speeds or move to different traffic lanes to avoid conflicting with the departing vehicles. These maneuvers may have negative impacts on traffic safety. Therefore, implementing the revised method for calculating intersection sight distance, as presented in this paper, may ultimately reduce traffic collisions at TWSC intersections.

Effects of Pedestrian Crossing on Minor Road Capacity at Two-Way Stop-Controlled Intersections

Two-way stop-controlled (TWSC) intersections have been used extensively in the United States and other parts of the world when traffic signal control is not warranted. However, it was found that when a major road vehicle yields to crossing pedestrians, minor road traffic could use this extra gap, which tends to improve the capacity of some minor vehicle movements. The current capacity modeling methods did not take into account the effects of the pedestrian crossing on minor road capacity. This paper proposes an analytical model to quantify the increased capacity of minor street movements contributed by minor street pedestrian crossings and validates the model using both field data collected at a three-leg TWSC intersection and through the stochastic simulation method. A sensitivity analysis was performed to reveal the impacts of various factors on minor road capacity. In general, it was found that minor road left-turn capacity at the study intersection was positively correlated to pedestrian crossing volume, yielding rate, and pedestrian crossing time. Besides, modeling results showed that under relatively heavier conflict traffic volume conditions, the effect of the pedestrian crossing on increased capacity on the minor road was more significant.

Modeling two-way stop-controlled intersection crashes with zero-inflated models on Louisiana rural two-lane highways

Intersection safety continues to be a crucial issue throughout the United States. In 2016, 27% of the 37,461 traffic fatalities on U.S. roadways occurred at or near intersections. Nearly 70% of intersection-related fatalities occurred at unsignalized intersections. At such intersections, vehicles stopping or slowing to turn create speed differentials between vehicles traveling in the same direction. This is particularly problematic on two-lane highways. Research was performed to analyze safety performance for intersections on rural, two-lane roadways, with stop control on the minor roadway. Roadway, traffic, and crash data were collected from 4148 stop-controlled intersections of all 64 Parishes (counties) statewide in Louisiana, for the period of 2013 to 2017. Four count approaches, Poisson, Negative Binomial (NB), Zero-inflated Poisson (ZIP) and Zero-inflated Negative Binomial (ZINB) were used to model the number of intersection crashes for different severity levels. The results indicate that ZIP models provide a better fit than all other models. In addition to traffic volume, larger curve radii of major and minor roads and wider lane widths of major roads led to significantly smaller crash occurrences. However, higher speed limits of major roads led to significantly greater crash occurrences. Four-leg stop-controlled intersections have 35% greater total crashes, 49% greater fatal and injury crashes, and 25% greater property damage only (PDO) crashes, relative to three-leg intersections.

Efficiency and safety assessment of suburban highway access management

Congestion and traffic accidents often take place at the entrances and exits of highways. However, reasonable access management and design can greatly mitigate congestion and accidents. This paper discusses the field of suburban highway access management by introducing three typical suburban highways access management models, including the two-way stop-controlled intersection, simplified restricted crossing U-turn (RCUT), and interchange with right-in right-out. To ensure better efficiency and safety, the simulations were conducted in VISSIM and Surrogate Safety Assessment Model (SSAM) software. The travel time, delay, and throughput are used as the efficiency indexes, and the traffic conflicts are used as safety indexes to quantify the access management performance. The results show that the total delay at an interchange with right-in right-out decreased by 40.5%, and the conflict decreased by 50.0% more than a two-way stop-controlled intersection design, as well as the total delay decreased by 30.7% and the conflict decreased by 67.4% more than a simplified RCUT design.

Efficiency and safety assessment of suburban highway access management

Congestion and traffic accidents often take place at the entrances and exits of highways. However, reasonable access management and design can greatly mitigate congestion and accidents. This paper discusses the field of suburban highway access management by introducing three typical suburban highways access management models, including the two-way stop-controlled intersection, simplified restricted crossing U-turn (RCUT), and interchange with right-in right-out. To ensure better efficiency and safety, the simulations were conducted in VISSIM and Surrogate Safety Assessment Model (SSAM) software. The travel time, delay, and throughput are used as the efficiency indexes, and the traffic conflicts are used as safety indexes to quantify the access management performance. The results show that the total delay at an interchange with right-in right-out decreased by 40.5%, and the conflict decreased by 50.0% more than a two-way stop-controlled intersection design, as well as the total delay decreased by 30.7% and the conflict decreased by 67.4% more than a simplified RCUT design.

Evaluation of augmented reality cues to improve the safety of left-turn maneuvers in a connected environment: A driving simulator study

Left-turns are some of the most dangerous maneuvers drivers face as they involve a complex decision-making process. Indeed, drivers must wait for an adequate gap in oncoming traffic to safely complete a left-turn maneuver. In this context, incorrectly assessed gaps can lead to severe crashes and severe traffic delays at intersections. This study tests the potential of Augmented Reality (AR) technology, built into connected vehicle technology, to improve the safety of left-turn maneuvers of connected vehicles by adding visual virtual information to the driver. To achieve this goal, a driving simulator study was carried out. The effectiveness of the system was tested, and the ability of young drivers to detect adequate gaps between vehicles in the opposite lane (with right of way) to safely turn left was assessed with and without AR warnings at a two-way stop-controlled intersection under a connected vehicles environment. In the scenario projected on the simulation screen, three different virtual warnings were displayed and tested: a green/red traffic light, which informs the driver of the availability of an appropriate gap between opposing vehicles; a traffic light with a timer showing the number of seconds available to safely perform the left-turn maneuver; a traffic light with an additionally activated audio warning system. Significant positive effects of AR warnings on driving performance and traffic safety were observed: the number of safe left-turns increased and the delays at the intersection decreased. In addition, AR signaling improved driving behavior both during the waiting time, with many more drivers waiting for the gap in front of the stop line to avoid disrupting oncoming traffic, and turning movement, reducing the average time it took to complete the left-turn maneuver. This study confirmed the great potential of AR and connected vehicle technologies to improve general safety conditions on the road network, especially under risky situations and difficult maneuvers.

Analyzing variations in spatial critical gaps at two-way stop controlled intersections using parametric and non-parametric techniques

At two-way stop controlled (TWSC) intersections drivers on minor stream are generally at risk because of the difficulty in judging safe gap between major stream vehicles. Any misjudgment by the driver while choosing gap may result in a collision with major stream vehicle. This paper provides important insights for determining and analyzing spatial critical gaps of drivers at high speed and medium speed TWSC intersections. The critical gap line (CGL) fitted for the accepted and rejected gaps using parametric (binary logit model-BLM) and non-parametric (support vector machines-SVM) techniques gives critical gap values at 15th, 50th and 85th percentile speeds. The evaluation of spatial critical gap with respect to major road vehicle (conflicting vehicle) speed makes it easier to understand the impact of variation in speed on spatial gaps accepted by the drivers on the minor road. The logit models developed revealed that the probability of accepting gap decreases with increase in the speed of the conflicting vehicle and it increases with increase in the distance of conflicting vehicle. The spatial critical gaps estimated using support vector machines were found in close approximation with those estimated using binary logit model. The study results showed that SVMs have very good potential to be an alternative tool for the estimation of driver's critical gap. The spatial critical gaps corresponding to 15th, 50th and 85th percentile speeds for medium speed intersections were 32 m, 38 m and 46 m respectively and for high speed intersections these values were 64 m, 76 m and 104 m respectively. The increase in the magnitude of gap value with respect to the percentile speed clearly states the effect of speed on spatial gaps. The insights from the study can be used to suggest various measures to improve the safety of crossing drivers at uncontrolled intersections. • The study provides important insights for analyzing spatial critical gaps at high speed and medium speed uncontrolled intersections. • BLM and SVM are used as a linear classifiers to fit decision boundary between accepted and rejected gaps. • The spatial critical gaps estimated using BLM and SVM corresponding to 85th percentile speed are 46 m and 45 m respectively. • SVMs have very good potential to be an alternative tool for the estimation of driver's critical gap.

Queue-Based Guidance for Signalization Consideration at Two and Three-Legged Intersections

This research collected and analyzed gap acceptance in North Carolina to develop a data-driven method for determining the need for considering additional signalization analysis at intersections with fewer than four legs. This method can be used for movements that merge with or cross two lanes of oncoming traffic. It is intended to provide guidance and support to traffic engineers in their decision-making process. Charts are provided to determine the expected 95th percentile queue lengths for left-turn, right-turn, and U-turn movements crossing or merging with two lanes of conflicting traffic. This situation is typically present along four-lane roadways where a one-way primary movement opposes either a minor road right-turn movement or a left-turn movement, or in the case of a median U-turn opening. Adjustment factors to the conflicting flowrate were developed to account for the presence of upstream signalized intersections. This method less frequently recommends further signal consideration when compared with the Manual on Uniform Traffic Control Devices peak hour warrant, but is similar to the delay-based level of service D/E threshold for two-way stop-controlled intersections in HCM6 Chapter 19.

Effects of Signalization at Rural Intersections Considering the Elderly Driving Population

The main objective of this study is to quantify the safety impacts of signalization at Florida’s rural three-leg and four-leg stop-controlled intersections by estimating crash modification factors. The intersections are those in which stop signs are provided for the minor approaches or all-way stop-controlled intersections. The crash modification factors (CMF) are estimated using the cross-sectional method. Generalized linear models (GLM) and multivariate adaptive regression spline models (MARS) are employed with four years of Florida crash data. The K-nearest neighbor (KNN) and K-means clustering algorithms are implemented to identify the comparison sites which are sites having similar characteristics as those of the converted intersections. Furthermore, the quasi-induced exposure method is used to evaluate separately the safety effects of signalization for elderly and non-elderly drivers. According to the results, signalization contributes to an increase in property damage only (PDO) and rear-end crashes. In addition, elderly drivers are more at risk of being involved in such crashes than non-elderly drivers. In particular, at rural four-leg two-way stop-controlled intersections, signalization decreases crash severity, and a greater percentage of the decrease is observed for the elderly drivers than non-elderly especially when the intersection has a high level of major-road average annual daily traffic (AADT) and elderly driver proportion. This study also demonstrates that the MARS model shows a better model fit than the GLM model due to its strength in capturing nonlinear relationships and interaction effects among variables. This study’s findings have implications for both practitioners and researchers.

Investigating gap acceptance behavior at two-way stop-controlled intersections in China

ABSTRACTThe stop-controlled intersection is widely used all over the world. However, owing to the regional differences in driving behavior, its performance varies geographically. This study analyzed the stop behavior and critical gap using field data collected at 14 two-way stop-controlled intersections in Shanghai, China. A logistic model was established to estimate the stop probability of the minor movements. Then, the critical gap is estimated by employing the Raff method and maximum likelihood estimation based on the data of accepted gaps and rejected gaps. The measured values from this study were compared with the recommended values in HCM 2010. Results show that the main factors affecting the stop behavior include the intersection type, movements, traffic volume, and darkness. On average, the critical gap increases by 18.74% when the location of the intersection is changed from the central district to the outside district.