Road Safety Commissioner Kim Papalia has welcomed positive signs from early testing results within the Forrest Highway average speed safety camera zone.
The six month testing period of the camera technology used within the zone concluded on 30 April.
Mr Papalia said he is pleased that early data shows a downward trend in the number of speeding vehicles within the zone between Lake Clifton and Binningup.
"Although these cameras have not started issuing penalties against speeding drivers, the data has shown that they already act as a deterrent for speeding drivers," said Mr Papalia.
"Early data from the Australian Road Research Board (ARRB) tells us that soon after the cameras were installed, there was a 5-6% reduction in drivers recorded as speeding within the zone, that equates to around 25,000 drivers.
"The preliminary results from the Australian Road Research Board also found that in the first three months of the testing period, 35% of vehicles were found to speed within the zone.
However, 90% of those vehicles were found to be at low level speeds (0-9kmh), with 10% of those vehicles were travelling at more than 10kmh over the speed limit.
Between January 2012 and October 2016, there were five fatal and 15 serious injury crashes on that stretch of the Forrest Highway.
There were no crashes between October 31 2016 and December 31 2016, and no fatalities within the zone this year. Serious injury data for 2017 is not yet available.
“That stretch of the Forrest Highway was chosen as the test site for this technology in Western Australia, as it is a known crash black spot," said Mr Papalia.
"The crash statistics since the inception of the average speed safety camera zone provide positive evidence of their effectiveness at reducing speed travel speeds and the reduction of crashes resulting in death and serious injury.
"Slow down and we can save lives."
ARRB will compile the final report on test period results for the average speed safety camera zone once all remaining data has been compiled.