Pedestrian Danger Index – a novel surrogate measure of pedestrian safety at unsignalized crossings

Abstract

Objective The aims of the study are to assess pedestrian safety at unsignalized crossings and to develop a new surrogate measure to evaluate risks associated with vehicle-pedestrian interactions. The primary goal of developing a novel safety metric was to provide quick insights into pedestrian safety levels and conduct site assessments rather than predictive analyses. Methods Video surveys were conducted at multiple unsignalized crossing sites in Poland to record vehicle-pedestrian interactions. Vehicle and pedestrian trajectories were extracted using video image analysis. An interaction classification algorithm was introduced, based on relative movements of the two road users involved. Using selected video recorded interactions, an expert opinion survey was conducted in order to evaluate pedestrians’ perceptions of risk. The level of risk was modeled with a "danger degree function", incorporating passing distance, vehicle speed, and deceleration. Results Analyses revealed that smaller passing distance and higher vehicle speeds are linked to increased danger levels. Pedestrian Danger Index (PDI) was introduced as a new measure to assess pedestrian safety by averaging danger levels for all the observed pedestrian-vehicle interactions. Based on the sensitivity analysis, it is recommended to use a minimum of 4 survey days when calculating the PDI indicator. Conclusions The PDI offers a novel method for evaluating pedestrian safety at unsignalized crossings, though it has some limitations. This user-friendly surrogate safety measure relies on three key variables for computation: passing distance, vehicle speed, and vehicle deceleration rates. The formulated PDI equation can be used for analyzing pedestrian crossings without traffic signals. Further research is recommended to refine the PDI and enhance its effectiveness.