• Driver behaviours in moving passenger and heavy vehicles were covertly recorded.
• Driver distractions included mobile phones, reaching/holding and eating/drinking.
• 8.6% of passenger vehicle drivers and 14% of heavy vehicle drivers were distracted.
• Drivers were less distracted in high speed zones compared to low speed zones.
• Illegal mobile phone use was 2.0% and almost always concealed.
The diversion of a driver's attention from the essential tasks required when driving a vehicle has been demonstrated to significantly increase the risk of having a road crash. Mobile phone use by drivers is widely recognised as increasing crash risk, while many other common distractions, such as eating or adjusting vehicle controls, are also problematic but less well understood. This study was aimed at objectively measuring the prevalence of various in-vehicle distracting driver behaviours in moving traffic. Covert video surveillance was deployed, using specialist video camera systems at four elevated locations on South Australian roads. Video was recorded and then analysed by multiple independent researchers. A total of 920 drivers were observed in the footage, and 8. 9% of all drivers were observed to be potentially distracted. The majority of drivers were in passenger vehicles (94.6%) and among these drivers 8.6% were distracted in comparison to 14% of heavy vehicle drivers. The most prevalent driver distractions observed included mobile phone use (2.5%), reaching for, or holding an object (1.8%), eating or drinking (1.5%) and wearing headphones (0.9%). A higher speed zone was associated with a lower proportion of distracted driving behaviour. Reducing mobile phone use in vehicles through blocking technologies and police enforcement will decrease distracted driving and distraction related crashes; however, other in-vehicle distractions are also pervasive and require interventions to reduce distracted driving. Importantly, this methodology can be used to objectively monitor the prevalence of distracted driving behaviours over time and to evaluate interventions aimed at changing distracted driving behaviour.