Evaluating Safe Distance for Pedestrians on Urban Midblock Sections Using Trajectory Plots

Crossing by pedestrian at-grade on Indian urban roads is a very common phenomenon. Pedestrians cross the road at any undesignated locations to access the residential and commercial lands. Crossing by pedestrians is essentially a gap acceptance process where the pedestrian would evaluate the gap available in all the lanes to be crossed before entering the road. Availability of the gap would depend on traffic volume in the lane and acceptance (or rejection) of the gap would depend upon the perception of the pedestrians about the gap. This pedestrian-vehicle interaction is a complex phenomenon and has deep safety implications. Traffic conflict technique (TCT) is used by many researchers to quantify such interactions and time based surrogate safety measures have been suggested. In the present study, the distance based surrogate safety measure "Safe Distance (SD)" has been introduced based on the profound analysis of 310 separately identified pedestrian-vehicle interaction instances. The position of the pedestrian and the interacting vehicle was tracked, and the trajectory was plotted to visualize their lateral and longitudinal movement. Further, SD value was worked out for two separate cases, namely, vehicle pass first (VPF), and pedestrian pass first (PPF) based on pedestrian-vehicle interaction. Safety-Index threshold value has been developed for different category of vehicles based on vehicle speed as a variable. Results of the study reveal that the pedestrian will be at higher risk when SD is 1.75 m for VPF case and 19 m for PPF case. This study results can be a supplement to the existing guidelines for pedestrian safety, and also provide insight to the practitioners in developing safe and efficient traffic facilities.