Prevalence and Self-regulation of Drivers’ Secondary Task Engagement: An Investigation of Behaviour at Intersections Based on Naturalistic Driving Data

Using data from the large-scale European Naturalistic Driving project (UDRIVE), this thesis explored the prevalence of engagement in secondary tasks whilst driving through intersections and investigated whether drivers self-regulate such behaviour in response to variations in roadway and environmental conditions. The thesis also examined the possible influence of secondary task engagement on turn signal usage at intersections. To these ends, 1630 intersection cases were randomly sampled from the UDRIVE dataset for coding and in-depth analysis. In-vehicle video recordings and recordings of external scenes in the selected sample were coded for precisely defined categories of secondary tasks and related contextual variables. The findings indicated that nearly one-quarter of the total driving time at intersections was spent on secondary activities and that such engagement decreased with increasing age. The drivers were less likely to occupy themselves with secondary tasks as they passed through an intersection itself, as opposed to the approach (upstream) and exit (downstream) phases. The drivers also tended to perform secondary tasks less frequently when their vehicles were moving than whilst they were stationary, when they did not have priority to pass through intersections compared with when they had priority and in bad weather conditions than in fine weather situations. Lastly, the drivers showed less inclination to use turn signals when they were engaged in secondary tasks than when they were driving under normal baseline conditions. In conclusion, the drivers appeared to self-regulate secondary task engagement according to road and driving situations, specifically when the primary task of driving becomes progressively challenging. This self-regulation behaviour was particularly strong for more complex and, therefore, more demanding secondary activities. The outcomes provide initial evidence that can serve as reference in targeting countermeasures and policies related to safe driving and managing distractions.