Beyond the billboard: A review of other external sources of driver distraction.

Road corridors contain countless sources of distraction, each carrying the potential to draw drivers' eyes and minds off roads, thus increasing the risk of a crash. While the impact of billboards on driver distraction has received considerable attention, empirical data for other types of roadside advertising signs is very limited. Furthermore, the existing research examining other potential external sources of distraction is fragmentary, which makes it difficult to develop evidence-based road safety policies to mitigate risk. Therefore, the aim of this study was to conduct an exploratory review to ascertain and synthesise the available distraction-related literature for various types of roadside advertising signs (excluding billboards) and other potential external sources of distraction in the road corridor. Based on distraction-related theory and existing literature, 58 predefined categories of potential distraction sources were developed to guide an exploratory literature search using the Scopus database. Fourteen documents relating to external distraction sources were identified in the database search with a further five studies found using a backwards citation chaining search (N=19). However, no studies for non-billboard types of roadside advertising signs were found. Studies included those that investigated driver distraction in relation to construction zones, commercial logos contained within official traffic management Dynamic Message Signs (DMS) and service (logo) signs, drones, murals, roadside memorials and wind turbines. While one study investigated whether an external source of distraction can have a positive effect on driver behaviour, the remainder focused on the potential negative impacts on road safety of these sources of distraction. A key finding of the review is that crash risk increases when drivers continue to visually and cognitively engage with a source of distraction. Overall, the studies provide insights into the types of distractions that can be encountered in road corridors and the impact they can have on driver behaviour. However, more research is required before the mechanisms and pathways involved in these types of distractions can be effectively conceptualised, and thereby mitigated to reduce the burden of distraction risk and road trauma.