Defining and applying surrogate safety measures and behavioural indicators through site-based observations

Abstract

This dissertation looks into surrogate safety measures and behavioural indicators that are collected through site-based observations. Surrogate safety measures are defined as measurements that are used to describe the relationship between two road users in a traffic event for the purpose of quantifying the crash probability and/or the potential crash severity in a meaningful way. The main goal of this dissertation is to contribute to filling methodological knowledge gaps in site-based observations of surrogate safety measures and road users’ behaviour, and to investigate how such observations can be used to study road safety issues for which crash data appear to be less suitable. The dissertation includes a scoping review that investigates in a comprehensive and quantitative way how surrogate safety measures have been applied so far. The theoretical framework and first implementation of a new indicator, Extended Delta-V, are presented. Three case studies have been conducted that aim to further investigate how site-based observations of road users’ behaviour and interactions could supplement or even replace surrogate safety measures, especially when severe events take place infrequently and/or dispersed. The case studies relate to: 1) the safety of bicyclists on bus lanes shared with bicyclists, 2) drivers’ behavioural adaptions caused by wind turbines alongside the roadway, and 3) differences in drivers’ interactions at right-hand priority intersections and priority-controlled intersections. The case studies provide some safety-relevant insights into topics that have rarely been addressed in scientific literature before. Policy and design implications are discussed.