ASSESSMENT OF PEDESTRIAN SAFETY AT SIGNALIZED INTERSECTIONS USING TRAFFIC CONFLICT TECHNIQUE

Abstract

The interaction between pedestrians and vehicles at a signalized intersection is a usual scenario in urban locations where both share a common space on the road. Due to the rapid growth of vehicular traffic in developing countries like India, pedestrian-vehicle conflicts are increasing tremendously. The exposure of pedestrians to the risk of crashes remains a subject of attention for transportation planners and engineers. Historical crash data are often used to analyze the safety of road users at the intersections. However, safety assessment based only on crash records has many limitations. Unreliable crash data and under-reporting of crashes are some of the major issues that makes the safety assessment difficult. These limitations have led to the development of using a proactive approach commonly known as ‘Traffic Conflict Technique’ (TCT). The ‘Traffic Conflict Technique’ is an indirect, short-term, proactive safety technique that is being used as an alternative to historical approach for the reliable and faster safety evaluation. The first objective of the thesis aims to evaluate pedestrian safety by examining the interaction between pedestrians and right-turning traffic (left-hand driving) at signalized intersections using Traffic Conflict Technique. Five time-based conflict indicators, namely, Post Encroachment Time (PET), Time to Vehicle (TTV), Deceleration to Safety Time of pedestrians (DSTped), TTA (Time to Accident) and Deceleration to Safety Time of vehicles (DSTveh) have been utilized in this study to analyze the conflict situation. TTA is defined as the time that remains until a collision happens if the road user (pedestrian or vehicle) maintains the same speed and path when it realizes an abrupt change in traffic conditions (Archer and Young, 2010). Vehicle TTA and Pedestrian TTV are used separately for vehicles and pedestrians, respectively. Deceleration-to-Safety Time (DST) is defined as the necessary deceleration to reach a non-negative PET value if the movements of the conflicting road users remain unchanged (Archer, 2005). Again, DST has been calculated separately for both the road users- vehicles and pedestrians as DSTveh and DSTped, respectively. The K-mean clustering technique has been utilized to classify the conflict indicators into four levels of severity. The risk-taking behaviour of the pedestrian was decided on the basis of the values of the conflict indicators lying in the range of highest risk degree. A binary logistic regression model is developed to identify significant contributing factors on the risk-taking behavior of pedestrians. i The unsafe interactions among road users are often seen on urban networks of India. The conventional transportation planning method deals with this problem by segregating different modes to minimize intermodal conflicts. However, another school of thought recommends that the spaces should be designed to ensure minimum segregation between road users by removing physical barriers and eliminating rules. Once the rules are lifted, the road users become attentive towards the surroundings, and hence, spontaneous order takes place. The second objective of this study is to explore the yielding behavior of road users during conflicts and analyze the spontaneous order developed at intersections. The modal dominance was examined in terms of whether pedestrian yields to a vehicle or vice versa. Two multiple linear regression models were developed to analyze the effect of various factors such as speed and volume of pedestrians and vehicles, and size of intersection) on the number of conflicts and the proximity of conflicts. When a pedestrian yields to a vehicle while crossing, the dominance of the vehicle exists at the intersection. When a vehicle yields to a pedestrian while crossing, the dominance of the pedestrian exists at the intersection. The dominance of pedestrians and vehicles was predicted with the help of the binary logit model. The third objective of the study examines the violation behaviour of pedestrians at the signalized intersections in India. The study results show that approximately 44.6% of pedestrians that arrive during the red phase violate the signals. The violation prevalence is high is in the latter half of the red-light period. Further, the pedestrian-vehicle conflicts during the signal violations have also been explored in this study. The yielding behaviour of the road users during conflicts is found to vary in the beginning, middle and end of the red phase. The study utilized the conflict indicator ‘Post Encroachment Time’ (PET) to determine the proximity of conflicts during the violation. The severity levels of the conflict were determined with the help of the Swedish Traffic Conflict Technique (STCT) using ‘Time to Accident’ (TA) and ‘Conflicting Speed’ (CS). A generalized ordered logit model has been utilized to identify the factors (i.e., traffic conditions, personal characteristics, and situational characteristics) that affect the severity level of pedestrian-vehicle conflicts. The results highlight the need for engineering countermeasures, education, and enforcement to deal with the non-compliance behaviour of pedestrians. Finally, the fourth objective focuses on pedestrian violation behavior while crossing at signalized intersections. With the help of hazard-based duration models, the waiting duration of red-light violators has been analyzed. In addition, the response time of pedestrians during conflict has also been modeled with the help of a hazard-based duration approach. Kaplan Meier survival curves have been plotted for both the duration, i.e., waiting time and response time. With the help of the semi-parametric Cox proportional hazard model, various factors have been identified related to the pedestrians' survival probability during crossings. The parametric accelerated failure time (AFT) model was utilized to identify the multiple covariates that affected the waiting time and the response time. The Weibull model was found to be the best fit for waiting duration analysis, while the Log-Logistic model was observed to be best fit for the study of response time. The developed models can help understand the external factors and personal features of the pedestrians in relation to the risk involved during violation crossings. The present study comprehensively evaluated the pedestrian safety at urban locations using a proactive approach. This study evaluated the interaction between pedestrians and right turning traffic at signalized intersections and road users' yielding behavior during conflicts to predict the dominance of pedestrians and vehicles. Also, this thesis examined the non compliance behaviour od pedestrian while crossing the signalized intersections. The findings of this study can help to identify various factors that affect pedestrian-vehicle conflicts at signalized intersections. The comprehensive study of waiting time and response time can help to understand the behavioral characteristics of pedestrians while crossing at the intersections. The study results highlight the need for engineering countermeasures, education, and enforcement to deal with the pedestrian-vehicle conflicts at the signalized intersections.