Surrogate safety indicator for unsignalised pedestrian crossings

• Published in: Transportation research. Part F, Traffic psychology and behaviour Traffic psychology and behaviour, 2020-04, Vol.70, p.25-36
• Main Authors: Olszewski, Piotr, Dąbkowski, Paweł, Szagała, Piotr, Czajewski, Witold, Buttler, Ilona
• Format: Article
• Language: English
• Subjects: Automation; Blinking; Braking; Deceleration; Drivers; Image processing; Pedestrian crossings; Pedestrian safety; Pedestrians; Research projects; Signs; Surrogate safety indicator; Traffic accidents & safety; Traffic conflicts; Traffic control; Traffic flow; Traffic safety; Traffic speed; Vehicles; Video
• ISSN: 1369-8478; 1873-5517
• DOI: 10.1016/j.trf.2020.02.011

•Video-based safety assessment is proposed using detection of dangerous encounters.•Dangerous events are identified using vehicle speed, deceleration and min. distance.•A Dangerous Encounter Index is proposed as a surrogate safety indicator.•Crossing two lanes involves more risk than crossing one lane, given similar traffic.•Improvement of safety was observed with active signage involving blinking lights. Although the road safety situation in Poland is generally improving, the number of accidents at pedestrian crossings has not decreased in the last four years. This paper presents the results of the MOBIS research project, the aim of which was to develop surrogate safety indicators, based on detection of pedestrian-vehicle conflicts using video analysis. Pedestrian and vehicle traffic was filmed at two unsignalised pedestrian zebra crossings in Warsaw and Wrocław for over 40 days. Motion trajectories of vehicles and pedestrians were determined based on video processing. Several variables describing pedestrian-vehicle interactions were calculated, such as speed, post-encroachment time, distance between the participants, decelerations, etc. Classification of encounters was based on interactions of pedestrians and vehicles i.e. drivers yielding to pedestrians, vehicles passing just in front of, or behind pedestrians. Criteria for identification of dangerous encounters were selected with the assumption that it should be possible to automate the assessment process. The selected variables were: pedestrian-vehicle passing distance and the vehicle speed at that moment. Other criteria were used in cases of abrupt braking – deceleration exceeding 4 m/s2 and vehicle speed. A Dangerous Encounter Index is proposed as a surrogate safety indicator for pedestrian crossings. It relates the occurrence of dangerous events to exposure, defined as the number of pedestrian-vehicle encounters. The proposed index shows that crossing two lanes involves more risk than crossing one lane, given similar traffic flow. Some improvement of safety at both types of crossing was observed after active signage involving blinking lights had been introduced. The proposed method is a step towards automation of safety assessment.