Microscopic Traffic Risk Assessment at Signalized Intersections of a Bus Rapid Transit System

Bus rapid transit (BRT) systems have generated a tremendous positive change in road safety and public transport operations. However, the literature reveals the need for a quantitative preventive risk evaluation from a microscopic approach, integrated with outcomes from accident-based and behavioral research, which is the primary purpose of this paper. Its scope includes five components: (1) a novel risk diagnosis and mapping for three selected signalized intersections of the BRT system of (Columbia) City, using an event-based exposure definition of encounters, the Swedish Traffic Conflict Technique, and T-Analyst. (2) Cross-comparison of risk outcomes between intersections, in search for risk factors. (3) Validation of encounters against traffic volumes. (4) Exploration of the relationship between the number of observed conflicts and the number of reported accidents, using an American predictive model. (5) Discussion of the microscopic findings against the behavior declared locally and the limitations of the literature. As a result, the method provides detailed risk verdicts from 61 h of video data. BRT turning buses, and risky pedestrian behavior, are risk factors. Many pedestrians crossed intersections, taking risks without evident cause. The findings provide evidence for the hypothesis that such behavior is caused by several sources of overstimulation. In conclusion, encounters define the conflict frequency, overcoming the limitations of aggregate indicators. Traffic volumes do not fully explain the risk because most events were due to disobedience. The number of reported accidents was much higher than expected, considering the number of conflicts observed as evidence of aggressiveness. Cars and taxicabs drivers declared risky attitudes coinciding with our observations. BRT drivers’ behavior was acquiescent in most of the events observed, because the characteristics of BRT infrastructure. The findings comparison between signalized intersections and roundabouts allows for validating the methodology transferability.

The preventive approach herein proposed for microscopic traffic risk assessment, based on the traffic conflicts/encounters ratio, objectively provides detailed risk outcomes for an entire intersection or particular areas. The preventive risk ratio overcomes the limitations of the traditional indicator (crashes/exposure) by using a traffic conflicts technique, i.e., conflicts as surrogates for crashes, and an event-based exposure definition of encounters. This methodology allows practitioners to hypothesize the observed events’ causality and formulate countermeasures based on the exposure or the risk. A number of encounters and conflicts involved pedestrians crossing intersections at risk, without an apparent cause. Hence, this situation allows for identifying possible overstimulation sources for pedestrians, as a causality hypothesis. The proposed method helps to reduce traffic risk by verifying and rescheduling clearance times at signalized intersections according to the lengths of the BRT system vehicles. Moreover, traffic signs and sound signals reinforce the information about the imminent danger in case of recurrent distracted pedestrians at traffic lights. The process is also valid in roundabouts with mixed traffic, applying to any intersection.