The evaluation of the surrogate safety measures along a pedestrian confined ramp of an old bridge

Abstract

Pedestrians walk daily to meet their basic needs. Therefore, over the years it has been attempted to make urban context more livable, respecting the needs of weak road users. Pedestrian mobility is also growing strongly from the point of view of tourism, especially in the areas where government measures are taken to reduce vehicular flow in order to let the architectural and landscape assets more usable. Often tourist itineraries are made of narrow areas crossed by numerous pedestrians, leading to possible critical circumstances. The criticality is connected to a likely reduction of safety and use (comfort and possible delays). Confined spaces such as small streets or pedestrian bridges well exemplify the described situation. Particularly, pedestrian bridges are often composed of ramps with variable slopes and consist of different floors, making walking difficult and therefore reducing travel speed and limiting the mobility of users such as handicapped or elderly people. Starting from the geometrical evaluation of the old bridge of Mostar (BIH), this article provides some ideas for evaluating the safety of pedestrians during the journey on the bridge, under different flow conditions. The analyses were carried out starting from an estimate of pedestrian flows from video monitoring. Safety was then assessed thanks to the calculation of surrogate measures, based on the trajectories of individuals, obtained through tracking tools. Camera monitoring and inspections to survey infrastructure’s geometric features ease the procedure of data entering into image processing software. The evaluation of individual pedestrian trajectories and/or their interactions allows to estimate the movement variations through the study of parameters such as speed variation, pedestrian density and surrogate safety factors. Surrogate safety measures, indeed, are indicators calculated for a chosen pair of users interacting in the detected scene. Among these factors there are: relative speed (Delta-V), Time-To-Collision (TTC), Time Advantage (TAdv) and T2. All the above-mentioned kinds of measures are interesting to study generally the behavioural aspects of road traffic and, specifically, safety level and factors influencing it. The purpose of this work is to estimate the effects of induced pedestrian mobility on Mostar’s Ottoman bridge in terms of safety, with the aim of preventing negative scenarios that could lead to a bad infrastructural level of service. Keywords: road safety; pedestrian trajectories; surrogate safety measures.