A multidisciplinary investigation of the influence of the built urban environment on driver behaviour and traffic crash risk

Road trauma is a major source of death and disability which can be addressed by improving the safety of roads. Despite higher crash rates on urban roads than rural roads, less is known about the characteristics of the built urban environment (the road, surrounding environment and road user activity) that influence crash risk. It is essential to identify risk factors for crashes and to understand the underlying mechanisms driving risk before effective countermeasures can be developed. The overall aim of this thesis was to develop and apply a multidisciplinary approach to identify and understand the aspects of the built urban environment that influence crash occurrence. Research Component 1 of this thesis sought to identify characteristics of the built environment that were associated with crashes on complex urban roads. Beyond the effect of traffic volume and intersections, there was a lack of strong evidence regarding the influence of the built urban environment on crash risk, in particular, the effect of the surrounding environment was largely neglected. A comprehensive list was developed of characteristics of the built urban environment that were potential risk factors for crash occurrence. A cross sectional study was conducted using a novel phased modelling approach. It identified that, in addition to traffic exposure and road design, the roadside environment and facilities and amenities were associated with the frequency of multi vehicle, single vehicle and pedestrian vehicle crashes on strip shopping centre road segments in metropolitan Melbourne. Risk factors differed by crash type. Research Component 2 of this thesis comprised a case study to demonstrate how behavioural research methods may be employed to investigate the behavioural mechanisms underlying crash risk. Driving simulation was used to investigate the effect of roadside parking (identified as a risk factor for multi vehicle crashes in Component 1) and speed limit on driver behaviour. Drivers chose a lane position further away from the kerb and weaved less within their lane as the number of cars parked on the roadside increased. Perceived risk, discomfort, task difficulty and effort also increased. Increasing the speed limit of the road caused increases in perceived risk, discomfort, task difficulty, mental effort and physical effort. An increase in speed beyond that preferred in a given parking environment led to significant increases in the effort required to drive at that speed. No such threshold relationship with speed was discovered for ratings of risk, discomfort or task difficulty. As the number of parked cars varied, neither drivers' change in behaviour nor their choice of preferred speed served to maintain a stable level of risk or workload. Recommendations for countermeasures to address crash risk on urban roads with roadside parking were made. This thesis demonstrates a rigorous scientific process for applying two complementary methodological approaches to identify risk factors for crashes and understand their mechanisms. The innovative contribution of this thesis was the synergistic combination of cross sectional modelling and driving simulation to identify and further investigate risk factors for crashes. Implications for future road safety research and practice were discussed.