Attribute	Description
Vehicle Fleet	Larger (wider, longer), heavier and taller (higher centre of gravity) fleet, creating instability particularly in emergency manoeuvres and stopping. Heavier vehicles have longer stopping distances due to kinetic energy (not considered in vehicle safety testing) [@199654] Increasingly, private vehicles are now SUV, larger 4WD or utility vehicles (which are more like commercial vehicles so don’t have the same stability and braking performance of cars) Changes and improvements to vehicle safety standards, resulting in stronger, thicker, and wider A, B and C pillars in vehicles, restricting visibility Taller and wider vehicles in high density traffic restrict the forward vision of drivers, creating more blind spots affecting forward, side, and rear vision Vehicle technologies and/or their deployment have not adequately advanced to cover the additional risks associated with context change (multi-lane, high “flow”, and high-density)
Traffic Conditions	Doubling of daily traffic volumes, with increased exposure to high “flow” and high-density traffic conditions leading to longer periods of peak travel demand (increased from 1-2 hours over five days to 3-8 hours seven days a week). As much of the urban arterial road network reached capacity in the early 2000’s, the motorway system has absorbed much of the traffic growth Changing motorway trip patterns from carrying longer trips (average of 20-30 km) to shorter trip (averaging 10-15 km). Shorter trips mean higher concentrations and turnover of trips with many more vehicle interactions (lane changes, smaller gaps) to be negotiated by drivers Increased exposure to heavy traffic conditions accelerates driver fatigue
Trip Purpose	Change in trip purpose from transition to a service-based economy, with increased consumption of goods and services per capita linked to rising affluence, with motorways being an efficient conduit for cross-city and cross-suburb distribution and delivery to homes and businesses Around 80% of road travel is not commuting-related and the delivery of services and goods has shifted from being between the 500,000 premises of industry, business, and retail to all 2 million residential dwellings now potentially being daily service points with online shopping and many home-based services including delivery of meals and supermarket shopping. These daily service-based trips generally only require a driver (no passengers) and this is reflected in the increase in single-occupant crashes in Victoria (83% in 2021 compared to 70% in 1999) Changed driving patterns where people who drive for a living face different and often unfamiliar driving patterns everyday as they navigate to various businesses, suburbs, neighbourhoods and dwellings
Road Geometry	Motorways have been progressively widened from 2-3 lanes to 4-6 lanes, resulting in a non-linear increase in conflict points and necessary lane changes, markedly increasing lateral friction in the carriageway. The increased induced lane changing, when exposed to high-density traffic, compounds the complexity for drivers Often in widening motorways, running lanes and/or emergency lanes have been narrowed, leaving less room for vehicles to manoeuvre in emergency braking situations