Two-way Stop-controlled Research Articles

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.

Comparative Investigation of the Critical Gap at Priority Junctions: A Review Paper

The crucial gap is an important aspect of traffic characteristics that is used to assess the delay and capacity of individual car movements at priority junctions. Because traffic operations at priority junctions are complicated, many methods have been studied to find a more accurate critical gap. This research examines the standards established for these procedures throughout the previous seven decades, from Raff’s method in 1950 to the current day. These methods can be used anywhere in the world to determine the value of the critical gap for a mix of traffic, such as cars, vans, trucks, and motorcycles. The accuracy of these methods is assessed using factual data at two priority intersections, namely three-legged junctions (two-way stop-controlled (TWSC) with multilanes on main and minor streets). A total of 120 h of video camera recording was completed over the course of 5 working days in a week. This research identified Troutbeck’s, Wu’s, and Raff’s techniques as the most popular, offering consistent and robust critical gap values for both sides of the minor road at priority junctions.

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.

Localizing safety performance functions for two-way STOP-controlled (TWST) three-leg intersections on rural two-lane two-way (TLTW) roadways in Alabama: A geospatial modeling approach with clustering analysis

Safety Performance Functions (SPFs) can be used to predict the number of crashes for highway facilities by site characteristics, including traffic exposures and other specific site factors. The traditional approach to developing SPFs relies on factors that are observed in the data and has an unstated assumption that the relationships between safety performance and observed factors are stationary. However, there might be factors that are not captured by the data but also have significant impacts on roadway safety performance. These factors can lead to significant unobserved heterogeneity in safety performance at different sites. Failure to capture such unobserved heterogeneity in developing SPFs may result in biases and decrease the predictive accuracy. Given the interactions between highway traffic and roadway environments, the unobserved heterogeneity is likely related to the geographic space of the highway network. This study employs a spatial modeling approach, namely Geographically Weighted Negative Binomial Regression (GWNBR), to incorporate spatial heterogeneity into SPF model estimation. The GWNBR model can generate a local SPF for every site instead of a global SPF for one entire jurisdiction (e.g., a state) from the traditional approach. Local SPFs (or l-SPFs) are high-resolution and may be difficult for practitioners to use. To support the implementation of l-SPFs, this study proposes a method to aggregate l-SPFs to various geographic levels. This study first uses the 2014–2018 geo-referenced crash data from Alabama to develop l-SPFs for two-way STOP-controlled (TWST) three-leg intersections on rural two-lane two-way (TLTW) roadways in the state. The results show that l-SPFs vary substantially across Alabama. For example, the coefficients of traffic volume (AADT) on major roads range from 0.126 to 1.203 across different areas of the state. Then, an aggregation method based on K-means clustering is demonstrated to aggregate l-SPFs to various geographic levels of interest. The l-SPFs and their aggregation provide geographic flexibility in developing countermeasures and allocating funds to improve traffic safety considering local conditions.

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.

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.

Some New Developments in Two-Way-Stop-Controlled Intersections Procedures and Recommendations for a Future Version of the Highway Capacity Manual

The estimation of capacities and traffic performance at two-way-stop-controlled (TWSC) intersections has been the subject of investigations conducted by many researchers. The results of these investigations are incorporated in highway capacity manuals like the U.S. Highway Capacity Manual (HCM) or the German Handbuch für die Bemessung von Strassen (HBS). Although the underlying methodologies are similar, there are two major differences between the current HBS 2015 and HCM6: (a) the procedure for the impedance factor for movements of rank 4 and (b) the procedure for estimating the capacity of shared short lanes for both minor and major movements. In HBS 2015, new developments are accounted for and the accuracy of capacity and traffic quality estimations significantly improved. In HCM6, these two procedures have not been updated. Therefore, the replacement of the two procedures in HCM6 is recommended. In both HCM6 and HBS 2015, the procedures for calculating delays at shared lanes or shared short lanes are inaccurate and they also should be updated. In most cases, the delays are significantly underestimated. Recently, the authors have developed a new methodology dealing with this problem which can be easily incorporated into future versions of HBS and HCM. In this paper, the theoretical backgrounds of the three new methods are presented and major results are summarized. Compared with HCM6, the advantages of the new developments are highlighted. As a recommendation, three corresponding procedures for estimation of capacity and delay are given for potential use in a future version of HCM.

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.

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.

Capacity Analysis Procedure for Four-leg Non-standard Unsignalised Intersections

Procedures for capacity analysis of two-way stop controlled (TWSC) appeared in scientific literature in the 1970s. In addition to standard TWSC intersections, there are also non-standard unsignalised intersections. The main characteristic of these intersections is that two major approaches are not placed opposite, but next to each other. Because of the non-standard layout of the major and minor approaches, there are unique major and minor movements at these intersections. For these movements, standard procedures for capacity analysis of standard TWSC intersections cannot be used. This paper describes a procedure for capacity analysis of non-standard unsignalised intersections with a new model for rank distribution for all major and minor movements, as well as the conflict flow calculation, and the procedure for the calculation of potential and movement capacity, according to the non-standard layout of the major and minor approaches.

Multiobjective Evaluation in Countermeasure Selection at Two-Way Stop-Controlled Intersections: Considering Traffic Operation, Safety, and Environment

This study developed a procedure to conduct multiobjective evaluations in the traffic countermeasure (CM) selection process at two-way stop-controlled (TWSC) intersections. The economic benefits of three vehicle safety–related CMs were calculated considering not only safety impacts, but also operational and environmental impacts. First, for each CM, VISSIM simulation models were developed to obtain the average delay, vehicle emissions, and fuel consumption for the intersection before and after the treatment. The traffic operational impacts were calculated as the change in delay costs. The environmental impacts were calculated as the change in vehicle emissions and fuel consumption costs. Next, safety performance functions and crash modification factors were used to calculate the safety impacts as the crash reduction benefits for various CMs. Finally, the life-cycle cost method was used to combine the different components into the total benefit. The Monte Carlo simulation method was used to conduct uncertainty analysis through random sampling from probability descriptions of uncertain input variables to generate a probabilistic description of results. The findings showed, first, that the operational and environmental impacts accounted for a large proportion of the total impacts, which can significantly affect the selection of CMs. Second, the rankings of the CMs differ depending on whether the safety impacts alone are considered or different impacts are considered together. The study illustrates the detailed process of evaluating projects considering multiple objectives. The findings also explain how different objectives can have countervailing effects in improving motorist safety at TWSC intersections.

Time-of-day Visibility-based Pedestrian Gap Acceptance Model for Two-Way Stop Controlled Crossings

Conventional traffic engineering studies at two-way stop controlled (TWSC) pedestrian crossing locations have been largely interested in estimation of capacity and delay impacts due to pedestrian impedance. Review of the literature indicates that pedestrian gap acceptance behavior at TWSC locations has not been investigated in detail. The objective of this research was to obtain and use empirical observations from study sites in Alabama to develop pedestrian gap acceptance models at TWSC pedestrian crossings. Visibility due to daylight conditions was also explored. Discrete choice models with underlying normal and logistic distribution of error terms were developed. From the set of developed models, a probit model was found to be suitable for further empirical validation. Based on this model, gap length, presence of vehicle at minor street waiting for right of way, opportunity to cross the street in lag, and daylight visibility were found to affect pedestrian gap acceptance. This study broadens empirical pedestrian behavior model development to TWSC locations and is the first of its kind to elaborate on visibility impacts.

Operational Performance at Two-Way Stop-Controlled Intersections

When two cars approach the stop-controlled legs of a two-way stop-controlled (TWSC) intersection at the crossing of a major and a minor roadway, driver perception concerning which vehicle should be granted the right-of-way is often unclear. This confusion can increase if one of the drivers intends to execute a left turn. The research described in this paper was performed primarily to identify any safety issues with driver perception or understanding in the case of one left-turning vehicle with an opposing right-turning or straight-through vehicle at the stop-controlled legs of a TWSC intersection. The data collection involved filming and observing vehicle interactions at seven TWSC intersections in the cities of Bryan and College Station, Texas. The way left-turning vehicles responded to the TWSC intersection when an opposing vehicle was present was specifically evaluated. This scenario occurred 113 times for the seven intersection locations during a total evaluation period of approximately 25 h. For these 113 observations, the researchers performed statistical analyses and determined that the minor roadway volume and the first vehicle to approach the intersection significantly influenced driver behavior. The overall study findings confirm the hypothesis that drivers do not fully understand the appropriate (legal) maneuver protocols when stopped at TWSC locations.

Pedestrian Crossing Sight Distance: Lateral Clearance Guidelines for Roadways

No design guidelines are available for pedestrian crossing sight distance (PCSD) and associated lateral clearance on roadways. Guidelines are available only for intersection (vehicle) sight distance (ISD) at two-way stop-controlled (TWSC) intersections. This paper presents a new model for pedestrian crossing time that is used to establish a general model for lateral clearance at crossings located on curved (or straight) roadways. The model is applicable to all crossing types: TWSC intersections, midblocks, and freeway ramps. The model can be used to determine the maximum lateral clearance to the right or to the left of the crossing or the required lateral clearance at a specified location. The distance from the crossing within which on-street parking should be restricted to satisfy PCSD is also determined. A single spreadsheet that is applicable to all crossing types was developed. A comparison with ISD shows that lateral clearance needs for pedestrians are not satisfied by those currently available for vehicles. Design aids for all crossing types are presented. The method presented in this paper promotes pedestrian safety and should be of interest to the highway community.

Multi‐objective analysis of using U‐turns as alternatives to direct left turns at two‐way stop‐controlled intersections

SummaryThis study aims to propose a method to conduct multi‐objective analysis of traffic treatments by taking into consideration multiple external impacts. To illustrate the procedure, the economic benefit of converting a two‐way stop‐controlled (TWSC) intersection to a right turn followed by U‐turn (RTUT) intersection was calculated, considering not only the safety impacts but also the operational and environmental impacts. First, vissim simulation models were developed to obtain the total travel time, vehicle emissions, and fuel consumption for the intersection both before and after the treatment. The operational impact was calculated as the travel time saving benefits. The environmental impact was calculated as the reduction in vehicle emissions and fuel consumption costs. The safety impact was estimated as the crash reduction benefits for the RTUT treatment using safety performance functions and crash modification factors (CMFs). CMFs were estimated using meta‐analysis methods. Finally, the life‐cycle cost method was used to combine different components in the total benefit. The Monte Carlo simulation method was used to conduct uncertainty analysis by using random sampling from probability descriptions of uncertain input variables to generate a probabilistic description of results. The findings showed that, first, the benefits with the use of RTUT treatment can be countervailing even for a single objective. Second, the net present value associated with the RTUT treatment increased with an increase in the proportion of left‐turn traffic from the major street when the percentage of left‐turn traffic from the major street was from 0% to 22% and became stable after that. The study illustrates the detailed process of evaluating projects considering multiple objectives. This process offers policy and decision makers a solid and practical reference using existing guidebooks and software. The findings also provide suggestions about the suitable condition to install RTUT treatments at TWSC intersections. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of an Upstream Traffic Signal on the Capacity of a Downstream Two-Way Stop-Controlled Intersection

This paper investigates the platoon dispersion model that is part of the Highway Capacity Manual 2010 (HCM 2010) and is used to forecast downstream traffic flows for analyzing both signalized and two-way stop-controlled (TWSC) intersections. The paper focuses on the effect of platoon dispersion on proportion of time blocked, conflicting flow rate, and capacity flow rate for the major street left-turn movement at a TWSC intersection. Existing HCM 2010 methodology shows little effect on conflicting flow or capacity for various distances downstream from the signalized intersection. Two methods are suggested for computing the conflicting flow and capacity of minor stream movements at a TWSC intersection that have more desirable properties than the existing HCM method. Further, if the existing HCM 2010 method is retained, results suggest that the upstream signals model be dropped from the HCM method for TWSC intersections.

Impacts of Pedestrians on Capacity and Delay of Major Street Through Traffic at Two-Way Stop-Controlled Intersections

This paper aims to estimate the impacts of pedestrians on capacity and average control delay for the major street through traffic at two-way stop-controlled (TWSC) intersections. A procedure was proposed to estimate the expected delay for major street through vehicles based on the pedestrian arrival time and motorist yielding behavior. Field data were collected to calibrate the crucial parameters in the established models. The proposed models were then validated against field measured data. It was found that the calibrated models provided reasonable delay estimates. Based on the established models, sensitivity analyses were conducted to identify the effects of pedestrian arrival rate and motorist yield rate on the capacity of the major street through lanes at TWSC intersections. The results suggested that the capacity of the through movement would decrease with an increase in the pedestrian arrival rate. It was also found that, with the same pedestrian arrival rate, the capacity would decrease as the motorist yield rate became higher, and the magnitude of the capacity reduction would increase with an increase in the pedestrian arrival rate.

Empirical Evaluation of J-Turn Intersection Performance

Most crashes on high-speed rural expressways occur at intersections with minor roads. Through and left-turn movements on minor roads are especially susceptible. One low-cost alternative for improving safety of at-grade intersections on such expressways is the J-turn. This study evaluated the effectiveness of unsignalized J-turn intersection design in Missouri with field studies, crash analysis, and traffic conflict analysis. Field studies used detailed video-derived data at a J-turn site and a control site. Crash analysis included an empirical Bayes before–after safety evaluation of five J-turn sites. The empirical Bayes analysis found that the J-turn produced a 31.2% reduction in crash frequency for all crashes and a 63.8% reduction in crash frequency for injury and fatal crashes. Annual disabling injury crashes decreased by 91.6%, and minor injury crashes decreased by 67.9%. Annual right-angle crashes decreased from 8.6 to 0.8, a 90.2% reduction. No left-turn, right-angle crashes were reported after installation of the J-turn at any study site. The average time-to-collision conflict measure was four times higher at the J-turn site as compared with the two-way stop-controlled (TWSC) site of minor road turning vehicles; this result indicated greater safety at the J-turn site. The average wait time at the J-turn site (5 s) was half that at the control site (11 s), and the average travel time at the J-turn site was approximately 1 min more than at the TWSC site. Several study findings are transferable to J-turn installations in other states.

Proposed collision warning system for right-turning vehicles at two-way stop-controlled rural intersections

At two-way stop-controlled (TWSC) rural intersections, a right-turning driver who is departing the minor road may select an improper gap and subsequently may be involved in a rear-end collision with another vehicle approaching on the rightmost lane on the major road. This paper provides perceptual framework and algorithm design of a proposed infrastructure-based collision warning system that has the potential to aid unprotected right-turning drivers at TWSC rural intersections. The proposed system utilizes a radar sensor that measures the location, speed, and acceleration of the approaching vehicle on the major road. Based on these measurements, the system’s algorithm determines if there will be any potential conflict between the approaching and the turning vehicles and warns the driver of the latter vehicle if such a conflict is found. The algorithm is based on realistic acceleration profile of the turning vehicle to estimate its acceleration rates at different times so that the system can accurately estimate the time and distance needed for the departing vehicle to accelerate to the same speed as for the approaching vehicle. That realistic acceleration profile is established using actual experimental data collected by a Global Positioning System (GPS) data logger device that was used to record the positions and instantaneous speeds of different right-turning vehicles at 1-s intervals. The algorithm also gives consideration to the time needed by the driver of the departing vehicle to perceive the message displayed by the system and react to it (to start departure) where it was found that 95% of drivers have a perception–reaction time of 1.89s or less. A methodology is also illustrated to select the maximum measurement errors suggested for the detectors in measuring the locations of the approaching vehicle on the major road where it was found that the accuracy of the system significantly deteriorates if the errors in measuring the distance and the azimuth angle exceed 0.1m and 0.2°, respectively. An application example is provided to illustrate the algorithm used by the proposed system.