Incorporating Speed in a Traffic Conflict Severity Index to Estimate Left Turn Opposed Crashes at Signalized Intersections

2021 ◽  
pp. 036119812098616
Author(s):  
Alireza Jafari Anarkooli ◽  
Bhagwant Persaud ◽  
Craig Milligan ◽  
Joel Penner ◽  
Taha Saleem
Keyword(s):  
Methodological Approach ◽  
Score Function ◽  
Severity Index ◽  
Signalized Intersections ◽  
Linear Regression Models ◽  
Video Analytics ◽  
Left Turn ◽  
Traffic Conflicts ◽  
Traffic Conflict ◽  
Severity Levels

Rigorous evaluation of implemented safety treatments, especially for innovative treatments and those targeted at rare crash types, is challenging to accomplish with conventional crash-based analyses. This paper aims to address this challenge for treatments at urban signalized intersections by providing a methodology that uses surrogate measures of safety obtained from video analytics to predict changes in crashes. To develop this approach, left turn opposed traffic conflicts based on post-encroachment times, along with corresponding conflicting vehicle speeds, are first measured from video observations at signalized intersections. The conflicts are then classified into three severity levels using a risk score function defined by these measures. Multiple linear regression models are developed to relate left turn opposed crashes at the same intersections in the period 2009–2014 to the correspondingly classified conflicts. The results show strong relationships between the classified conflicts and crashes (adjusted [Formula: see text] of 85% and 94% for total and fatal/injury crashes, respectively). The results also reveal that the contribution of conflicts to the risk of crashes varies based on speed dimension of their severity, suggesting that neglecting speed as a factor in conflict severity levels may be at the expense of losing meaningful information. The models can be applied to estimate the change in crashes following a safety treatment by observing, through video analytics, the change in conflicts and speeds and using the crash-conflict-speed model. The methodological approach is viable for quickly evaluating all treatments and, in particular, innovative ones for which knowledge on safety effects is sparse or non-existent.

scholarly journals Safety evaluation of unconventional outside left-turn lane using automated traffic conflict techniques

2016 ◽  
Vol 43 (7) ◽  
pp. 631-642 ◽  
Author(s):  
Yanyong Guo ◽  
Tarek Sayed ◽  
Mohamed H. Zaki ◽  
Pan Liu
Keyword(s):  
Urban Areas ◽  
Safety Evaluation ◽  
Signalized Intersections ◽  
Video Data ◽  
Contributing Factors ◽  
Left Turn ◽  
Time To Collision ◽  
Traffic Conflicts ◽  
Traffic Conflict ◽  
The Right

The objective of this study is to evaluate the safety impacts of unconventional outside left-turn lane at signalized intersections. New designed unconventional outside left-turn lanes are increasingly used at signalized intersections in urban areas in China. The unconventional outside left-turn lane design allows an exclusive left-turn lane to be located to the right of through lanes to improve the efficiency and increase the capacity of left-turn movements. However, the design also raises some concerns regarding potential negative safety impacts. The evaluation is conducted using an automated video-based traffic conflict technique. The traffic conflicts approach provides better understanding of collision contributing factors and the failure mechanism that leads to road collisions. Traffic conflicts are automatically detected and time to collision is calculated based on the analysis of the vehicles’ positions in space and time. Video data are collected from a signalized intersection in Nanjing, China, where both traditional inside and unconventional outside left-turn lanes are installed on two intersection approaches. The other two approaches have only inside left-turn lanes. The study compared frequency and severity of conflict for left-turning vehicles as well as the percentage of vehicles involved in conflicts from the inside and outside left-turn lanes. The results show that the intersection approaches with outside left-turn lanes had considerably more conflicts compared to approaches without outside left-turn lanes. As well, the approaches with outside left-turn lanes had significantly higher conflict severity than the approaches without outside left-turn lanes. As such, it is recommended that the trade-off between the improved mobility and negative safety impact of outside left-turn lanes be carefully considered before recommending their installation.

Analysis of Pedestrian Conflicts with Left-Turning Traffic

1996 ◽  
Vol 1538 (1) ◽  
pp. 61-67 ◽  
Author(s):  
Dominique Lord
Keyword(s):  
Data Collection ◽  
Statistical Tests ◽  
Computer Programs ◽  
Signalized Intersections ◽  
Laptop Computer ◽  
Expected Number ◽  
Positive Correlation ◽  
Data Collection Process ◽  
Traffic Conflicts ◽  
Traffic Conflict

The interaction between pedestrians and left-turning vehicles at signalized intersections are examined using the traffic conflict technique. Paramount was a comparison of the safety of left turns at two types intersections: T-intersections and X-intersections (cross-intersections). Previous research has indicated that T-intersections are more dangerous to pedestrians. In preparation for the comparison several traffic conflict definitions and their applications to pedestrians were evaluated. Use of a laptop computer for data collection was tested. Eight sites taken from intersections in Hamilton, Ontario, Canada, were selected. A conflict recording methodology was developed for T-intersections and X-intersections that consisted of recording data at various times along the paths of pedestrians and left-turning vehicles, and recording traffic conflicts. Two computer programs were written for the data collection process: one for vehicles and one for pedestrians. Several statistical tests to relate traffic conflicts and the expected number of accidents were performed. These tests indicate that a positive correlation between traffic conflicts and expected number of accidents exists; they also suggest that T-intersections have a higher traffic conflict rate than X-intersections.

Comparison of Traffic Conflict Indicators for Crash Estimation using Peak Over Threshold Approach

2019 ◽  
Vol 2673 (5) ◽  
pp. 493-502 ◽  
Author(s):  
Lai Zheng ◽  
Tarek Sayed
Keyword(s):  
Confidence Intervals ◽  
Signalized Intersections ◽  
Estimation Methods ◽  
Crash Data ◽  
Time To Collision ◽  
Considerable Research ◽  
Traffic Conflicts ◽  
Peak Over Threshold ◽  
Traffic Conflict ◽  
Threshold Approach

Traffic conflict techniques have drawn considerable research interest and a number of conflict indicators have been developed. Previous studies have qualitatively analyzed indicator differences from their definitions and empirically investigated their similarities based on identified traffic conflicts. This study compares conflict indicators from a validity perspective by comparing crashes estimated from conflict indicators with observed crashes. The peak over threshold (POT) approach was employed for crash estimation. Four commonly used indicators are compared: time to collision (TTC), modified time to collision (MTTC), post encroachment time (PET), and deceleration to avoid a crash (DRAC). Based on the conflict and crash data collected from three signalized intersections, POT models are developed for different thresholds in the appropriate ranges, and crash estimation methods were proposed for individual conflict indicators. The identified conflicts and estimated crashes associated with different indicators are then compared. The results show that traffic conflicts identified by the four indicators vary, with MTTC generating the most accurate crash estimates. The crash estimates from TTC and PET are also reasonable but there is a tendency of overestimation for TTC and underestimation for PET. The crash estimates of DRAC are all outside the confidence intervals of observed crashes, which is likely related to the uncertainty of vehicle braking capacity.

scholarly journals Signal Control Method for through and Left-Turn Shared Lane by Setting Left-Turn Waiting Area at Signalized Intersections

2021 ◽  
Vol 13 (23) ◽  
pp. 13154
Author(s):  
Xiancai Jiang ◽  
Li Yao ◽  
Yao Jin ◽  
Runting Wu
Keyword(s):  
Control Method ◽  
Signalized Intersections ◽  
Signal Control ◽  
Signal Timing ◽  
Left Turn ◽  
Traffic Conflicts ◽  
Vehicle To Infrastructure ◽  
Waiting Area ◽  
Integrated Performance ◽  
Cooperation System

This paper proposes a signal control method for the through and left-turn shared lanes at signalized intersections to solve traffic conflicts between left-turn vehicles and opposing through vehicles by setting left-turn waiting area (LWA). Delays and stops are weighted to form an integrated performance index (PI) in a vehicle-to-infrastructure cooperation system. The PI models pertaining to all vehicles are established based on the LWA intersection. In addition, an optimized method of signal timing parameters is constructed by minimizing the average PI. VISSIM simulation shows that the average PI decreases by 6.51% compared with the original layout and signal timing plan of the intersection, since the increased delay of the side-road left-turn vehicles is insufficient to offset the reduced delay of the side-road through vehicles after the improvement. The sensitivity analysis shows that the greater the traffic volume of the phase including the through and left-turn shared lanes, the higher the operation efficiency of the LWA intersection compared with the typical permitted phase intersection. When the left-turn vehicles of the shared lanes in each cycle are less than the stop spaces, the LWA intersection can effectively reduce the average PI of the shared lanes. Furthermore, the more the stop spaces in the LWA, the lower the average PI in the same traffic conditions.

Modeling Traffic Conflicts between Pedestrians and Vehicles at Signalized Intersection Based on the Cellular Automata

2012 ◽  
Vol 178-181 ◽  
pp. 1881-1886
Author(s):  
Xiao Meng Li ◽  
Xue Dong Yan ◽  
Jiang Feng Wang
Keyword(s):  
Cellular Automata ◽  
Signalized Intersections ◽  
Signalized Intersection ◽  
Intersection Safety ◽  
Vehicle Density ◽  
Conflict Model ◽  
Traffic Conflicts ◽  
Traffic Conflict ◽  
Pedestrian Crossing ◽  
Main Factor

The traffic conflict between pedestrian and vehicle is a main factor that influences the intersection safety and capacity. In this paper, a conflict model that simulates the pedestrians and vehicles’ crossing behaviors when passing the pedestrian crossing area at signalized intersection is presented based on cellular automata method. Evolution rules for pedestrians, vehicles and conflicts between them are assigned. Four types of traffic conflict events and conflict areas are categorized and defined. On the basis of the simulation results, the pedestrian delay owning to traffic conflicts, the number of pedestrians’ conflicts, the conflict event and their relationships with the vehicle density as well as the pedestrian density are analyzed and discussed. This model reproduces realistic pedestrian-related traffic phenomenon effectively and can be used in more complex traffic environments at signalized intersections.

scholarly journals Safety evaluation of signalized intersections with automated vehicles at various penetration levels based on conflict analysis of simulated traffic

2021 ◽  
Author(s):  
Maria Espinosa
Keyword(s):  
Prediction Models ◽  
Safety Evaluation ◽  
Driving Behavior ◽  
Signalized Intersections ◽  
Automated Vehicles ◽  
Crash Frequency ◽  
Left Turn ◽  
Intersection Safety ◽  
Potential Safety ◽  
Traffic Conflicts

Automated vehicles (AVs) are expected to offer great benefits by potentially reducing crashes. The safety at signalized intersections is influenced by several factors, one of them being the driving behavior. By introducing AVs on the roads, the unpredictability of this factor will potentially decrease and eventually, reduce crashes. By using microsimulation, it was possible to use simulated traffic conflicts as indicators of potential crashes, to analyze the potential safety of signalized intersections in the presence of automated vehicles. The objective was to compare crash frequency for signalized intersections at various AVs penetration levels (0%, 50% and 100%) by using prediction models that relate crashes to conflicts. Furthermore, the effect on crashes of introducing hypothetical left turn treatments was also evaluated. The results indicated that intersection safety may improve in the presence of AVs. However, the safety effects of treatments may be reduced compared to the effects with no AVs.

scholarly journals Safety evaluation of signalized intersections with automated vehicles at various penetration levels based on conflict analysis of simulated traffic

2021 ◽  
Author(s):  
Maria Espinosa
Keyword(s):  
Prediction Models ◽  
Safety Evaluation ◽  
Driving Behavior ◽  
Signalized Intersections ◽  
Automated Vehicles ◽  
Crash Frequency ◽  
Left Turn ◽  
Intersection Safety ◽  
Potential Safety ◽  
Traffic Conflicts

Automated vehicles (AVs) are expected to offer great benefits by potentially reducing crashes. The safety at signalized intersections is influenced by several factors, one of them being the driving behavior. By introducing AVs on the roads, the unpredictability of this factor will potentially decrease and eventually, reduce crashes. By using microsimulation, it was possible to use simulated traffic conflicts as indicators of potential crashes, to analyze the potential safety of signalized intersections in the presence of automated vehicles. The objective was to compare crash frequency for signalized intersections at various AVs penetration levels (0%, 50% and 100%) by using prediction models that relate crashes to conflicts. Furthermore, the effect on crashes of introducing hypothetical left turn treatments was also evaluated. The results indicated that intersection safety may improve in the presence of AVs. However, the safety effects of treatments may be reduced compared to the effects with no AVs.

Modeling Capacity of Through Movement at Signalized Intersection Affected by Short Left-Turn Bay under Different Signal Settings

2021 ◽  
pp. 036119812110064
Author(s):  
Zihang Wei ◽  
Yunlong Zhang ◽  
Xiaoyu Guo ◽  
Xin Zhang
Keyword(s):  
Cycle Length ◽  
Signalized Intersections ◽  
Signalized Intersection ◽  
Essential Factor ◽  
Highway Capacity ◽  
Left Turn ◽  
Highway Capacity Manual ◽  
Proposed Model ◽  
Vehicle Demand ◽  
The One

Through movement capacity is an essential factor used to reflect intersection performance, especially for signalized intersections, where a large proportion of vehicle demand is making through movements. Generally, left-turn spillback is considered a key contributor to affect through movement capacity, and blockage to the left-turn bay is known to decrease left-turn capacity. Previous studies have focused primarily on estimating the through movement capacity under a lagging protected only left-turn (lagging POLT) signal setting, as a left-turn spillback is more likely to happen under such a condition. However, previous studies contained assumptions (e.g., omit spillback), or were dedicated to one specific signal setting. Therefore, in this study, through movement capacity models based on probabilistic modeling of spillback and blockage scenarios are established under four different signal settings (i.e., leading protected only left-turn [leading POLT], lagging left-turn, protected plus permitted left-turn, and permitted plus protected left-turn). Through microscopic simulations, the proposed models are validated, and compared with existing capacity models and the one in the Highway Capacity Manual (HCM). The results of the comparisons demonstrate that the proposed models achieved significant advantages over all the other models and obtained high accuracies in all signal settings. Each proposed model for a given signal setting maintains consistent accuracy across various left-turn bay lengths. The proposed models of this study have the potential to serve as useful tools, for practicing transportation engineers, when determining the appropriate length of a left-turn bay with the consideration of spillback and blockage, and the adequate cycle length with a given bay length.

Derivation of Decision Boundaries for Left-Turn Treatments at Signalized Intersections

2017 ◽  
Vol 2620 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Andrew Raessler ◽  
Jidong J. Yang
Keyword(s):  
Decision Making ◽  
Signalized Intersections ◽  
Maintenance Costs ◽  
Left Turn ◽  
Practical Guidelines ◽  
Decision Boundaries ◽  
Boundary Curves ◽  
Benefits And Costs

A new methodology is proposed to establish practical guidelines for four incremental left-turn treatments: ( a) permissive single left-turn lane, ( b) protected–permissive single left-turn lane, ( c) protected dual left-turn lanes with equal lane use, and ( d) protected dual left-turn lanes with unequal lane use. Decision boundaries were derived from the equilibrium at which the delays of two incremental treatments were equal. The benefits and costs associated with different left-turn treatments—including safety impact and construction and maintenance costs—also were considered. These benefits and costs effectually shift the boundary curves for more realistic decision making.

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