New research has helped explain the frequency of motorcycle collisions with cars, finding drivers are slower to notice motorbikes when there are fewer motorbikes on the road.
Dr Vanessa Beanland, from the Australian National University's (ANU) Research School of Psychology, found motorists would see and react to motorcycles up to three seconds faster when more motorbikes were on the road.
"When motorcycles were high frequency, drivers detected them on average 51 metres further away, compared to when they were at low frequency," Dr Beanland says.
"At a driving speed of 60 km/h, this allowed the driver an extra three seconds to respond."
More than 200 motorcyclists are killed on Australian roads each year, with 211 killed in 2013. Latest figures for 2011 found more than 7,500 motorcyclists were treated for injuries.*
Dr Beanland said the results could also help explain collisions between cars and bicycles. Government figures show 50 cyclists were killed on the roads in 2013.
Along with colleagues from Monash University and the University of Nottingham, Dr Beanland examined how the frequency of a specific type of vehicle in traffic can influence a drivers' ability to detect and respond to them.
They used a driver simulator to measure how quickly drivers saw motorcycles and buses on roads, with 40 adult drivers taking part. Half of the group encountered a high frequency of motorcycles and fewer buses, and half encountered fewer motorcycles and more buses.
"Being able to accurately see and identify objects around us is crucial to ensuring safe driving and avoiding collisions," Dr Beanland says.
"The results suggest that drivers have more difficulty detecting vehicles and hazards that are rare, compared to objects that they see frequently."
* Data from the Bureau of Infrastructure, Transport and Regional Economics, Road Deaths Australia, 2013, and the Australian Institute of Health and Welfare.