An analysis of more than 31,000 car accidents in Perth last year has revealed a growing proportion of rear-end and overtaking crashes - a trend considered systematic of congestion and gridlocked traffic systems all over the world.
The Main Roads WA analysis shows 44.9 per cent of last year's accidents were rear-end crashes - 5 percentage points higher than the total figure for the past five years.
And crashes involving overtaking accounted for 8 per cent of accidents, compared with the five-year rate of 6.4 per cent.
The data supports a 2012 assessment of RAC insurance claims that recorded a jump in rear-end accidents.
International studies over the past decade have found a direct link between rear-end car crashes and increased traffic congestion.
But while the frequency may have increased, rear-end accidents on congested roads are usually relatively minor because cars are travelling slower.
Interestingly, the Main Roads data for last year shows a fall in the number of accidents where speed was a factor.
In the US recently, an insurance company study in Atlanta found most rear-end accidents occurred during peak times and were caused by one car following the car in front too closely or by a distracted motorist.
Studies by the Institute for Road Safety Research in Amsterdam found rear-end accidents often occurred at the end of congestion queues, particularly when drivers were surprised by the gridlock.
A University of Adelaide study in 2005 found rear-end accidents occurred more often in congested traffic, at intersections and when vehicles turned right.
It found these factors increased the likelihood of hitting slowing or stationary vehicles.
Shadow transport minster Ken Travers said the increase in the proportion of overtaking accidents was a clear sign of congestion and the frustration it caused motorists.
"We need to be investing in a balanced transport system that sees the expansion of our rail and targeted road upgrades," he said.
"We need a long-term, soundly based plan to address congestion across Perth."