Congestion in Perth is worse in the morning, with freeway speeds reduced to only 20km/h.
These are the key findings of the first travel time study conducted across the metropolitan area to identify the extent of Perth's congestion problem during morning and afternoon peak times.
The RAC-commissioned study concentrated on 21 routes - covering more than 500km of road, three freeways and seven highways.
It found that in sections of Perth's freeway system - where the speed limit is 100km/h - motorists were travelling at average speeds as slow as 20km/h.
Traffic on Tonkin Highway near the intersection with Horrie Miller Drive fell to an average 14km/h.
The study also found that congestion was not only affecting traffic coming into the CBD but also east-west travel.
"The travel time study shows the enormity of the transport task," RAC head of advocacy Matt Brown said.
"Rapid population growth, major developments around the CBD and our strong economic performance have created the perfect storm in terms of congestion.
"With the RAC's own modelling projecting an additional one million motorised vehicles on WA roads by 2020, the need for increased investment in more efficient roads and better public transport is critical."
Of the freeways, the Mitchell performed the worst. Between Clarkson and the city, motorists spent half their commute in congestion. In the morning peak, it took an hour to travel from Clarkson.
The RAC has used the study results to produce interactive maps of 13 key routes that show average speeds on separate sections of each journey.
For example, on the Fremantle-to-Perth route, it found the worst morning congestion was on Stirling Highway between Napoleon Street and Queenslea Drive where average speeds fall to 19-21km/h.
In the afternoon, it is worse from Leura Avenue to Stirling Road. Slow segments are also apparent near the University of WA, the Fremantle traffic bridge and Peppermint Grove.
"The travel time study has been released by the RAC to contribute to the debate around congestion, assist in identifying traffic hotspots and promote the importance of land use and its planning," Mr Brown said. The data was collected by timing journeys four to six times between 7-9am and 4-6pm.More information on the study is available at http://rac.com.au/ractime
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