Climate and its many weather manifestations can help explain annual variations in fatalities and casualty crashes. Part 1 of a 3-part series identifies the breadth of weather factors which collectively contribute to crash risk reviewing and consolidating relevant research. The series identifies the need for interventions in advance of and during certain weather events, providing pathways for further research. The key climate drivers for Victoria produce complex interactions forming short-term (hours, days, weeks) and long-term (months, years, decades) weather patterns that influence crash occurrence and their spatial and temporal distribution across the state. Although analysis of Victorian crash records found weather was involved in at least 10% of fatal and casualty crashes, this is considered under-estimated as many weather-related events are not recorded nor considered in crash analysis. Spatial distributions of annual and daily crashes show alignment with movement of weather patterns across Victoria observed in Bureau of Meteorology synoptic charts, particularly in relation to low pressure systems and troughs, duration of damp pavement conditions, suddenly changing/unseasonal events, and periods of extreme heat and cold. Understanding how climate influences variations in crash occurrence can be used to develop appropriate strategies to improve road safety and help reach the target of zero deaths.

This paper is Part 2 of a three-part series illustrating how climate phenomena and weather metrics vary within a year and between years that can effect road safety. Part 1 identified the breadth of weather factors collectively contributing to crash risk and consolidated relevant research. The key climate drivers for Victoria produce complex interactions forming short-term and long-term weather patterns influencing crash occurrence and their spatial and temporal distribution across the state. The study found that the Southern Annular Mode (SAM) with its roughly 14-day cycle has the most significant influence on Victorian casualty crashes (also cyclic). A Chi-Square Goodness-of-Fit Test showed a statistically significant association (at the 0.05 significance level) between casualty crash numbers and each of the climate drivers. For fatal crashes, however, there was no statistically significant association, likely due to low numbers and randomness. Whilst this paper focuses on Victoria, other jurisdictions can use the approach presented using their local context of climate, latitude, and geography to identify patterns and influences on crashes. Understanding climate influences on crash occurrence within and between years assists strategy development for improving road safety and reaching the target of zero deaths.

This paper is the last of a three-part series. Part 1 identified the breadth of weather factors collectively contributing to crash risk and consolidated relevant research. Part 2 illustrated the cyclic nature of climate, weather, and crashes and how they vary over time. In part 3, the differences in weather conditions on days with high and low casualty crash numbers, days with high fatal crash numbers, and long sequences of days with and without fatal crashes were analysed using readily available Bureau of Meteorology (BOM) metrics: maximum and minimum daily temperature, daily rainfall, 6-hour synoptic charts, daily solar radiation, and water vapour pressure (for 9am and 3pm). The results showed marked differences between high and low casualty crash days. Spatial distributions of daily crashes show alignment with the movement of weather patterns across Victoria as observed in synoptic charts, particularly in relation to low pressure systems and troughs, likely duration of damp pavement conditions and periods of extreme heat and cold (well above or well below average for that time of year in that location). Understanding how specific climate and weather events can influence crash risk may help develop additional strategies to improve road safety and reach the target of zero deaths.

Changes in the way the road network is used over recent decades have altered the quantity, types and causes of crashes on all roads, especially those with high traffic demand such as motorways. As “flow” increases, density rises, vehicles drive closer together more frequently, and the required reaction time is often less than the headway between vehicles. Vehicles are now heavier, wider, and taller, and in heavy traffic, drivers’ forward vision is greatly reduced. Dynamic traffic conditions (nucleations, shockwaves, congestion) make driving tasks more complex, elevating crash risk. Often conditions are beyond human and vehicle capability. Newly available metrics allow new questions to be asked, highlighting unsafe headways and clearance distances, underestimation of lane changing, and changing crash proportions. There are opportunities for new initiatives to be implemented to utilise this expanded understanding and to address the changed driving context.