Adjustments of Speed and Path when Avoiding Collisions with Another Pedestrian

Markus Huber,Stefan Glasauer,Joachim Hermsdörfer,Katrin Faschian,Yi-Huang Su,Melanie Krüger,Markus Lappe

doi:10.1371/journal.pone.0089589

Abstract

When walking in open space, collision avoidance with other pedestrians is a process that successfully takes place many times. To pass another pedestrian (an interferer) walking direction, walking speed or both can be adjusted. Currently, the literature is not yet conclusive of how humans adjust these two parameters in the presence of an interferer. This impedes the development of models predicting general obstacle avoidance strategies in humans’ walking behavior. The aim of this study was to investigate the adjustments of path and speed when a pedestrian is crossing a non-reactive human interferer at different angles and speeds, and to compare the results to general model predictions. To do so, we designed an experiment where a pedestrian walked a 12 m distance to reach a goal position. The task was designed in such a way that collision with an interferer would always occur if the pedestrian would not apply a correction of movement path or speed. Results revealed a strong dependence of path and speed adjustments on crossing angle and walking speed, suggesting local planning of the collision avoidance strategy. Crossing at acute angles (i.e. 45° and 90°) seems to require more complex collision avoidance strategies involving both path and speed adjustments than crossing at obtuse angles, where only path adjustments were observed. Overall, the results were incompatible with predictions from existing models of locomotor collision avoidance. The observed initiations of both adjustments suggest a collision avoidance strategy that is temporally controlled. The present study provides a comprehensive picture of human collision avoidance strategies in walking, which can be used to evaluate and adjust existing pedestrian dynamics models, or serve as an empirical basis to develop new models.

Highlights

When walking in a shopping center or in a train station, pedestrians usually cross their paths with dozens of other people without colliding into them
We investigated whether and how pedestrians, walking at different speeds, adjusted their movement path and speed in the presence of a human obstacle who crossed at different angles without reacting to the pedestrian’s behavior
For the main effect of scenario, post-hoc comparisons revealed that turning started closer to point of minimal distance (PoMD) in the 45u and 90u scenarios than in the 135u scenario, and in the static and 180u scenarios, all p’s,0.05, while the former and the latter groups did not differ amongst themselves

Summary

Introduction

When walking in a shopping center or in a train station, pedestrians usually cross their paths with dozens of other people without colliding into them. Walking path refers to the spatial parameter (i.e., changes in position) of a pedestrian’s trajectory, regardless of the temporal evolution. The combination of these two parameters allows for infinite possibilities to avoid collisions with obstacles, the observed movements appear to exhibit stereotypical trajectories within and across people [1] [2]. This indicates that pedestrians use specific strategies to avoid obstacles while moving towards their intended locations. While the adjustment of path can always lead to successful obstacle avoidance, the adjustment of speed alone may not be sufficient. Imagine a person standing in your way or approaching you in a head-on encounter: collision avoidance in this case cannot be achieved without changing the path

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