If the speed limit on the Southern Outlet is not reduced, Transport Commissioner Gary Swain fears another fatal crash would occur.
On Thursday, the Department of State Growth announced it would be reducing the speed limit in both directions.
From the Howick Street intersection, to the Bass Highway interchange, the speed limit will become 90km/h.
The change is off the back of a fatal crash in 2018.
There have been nearly 140 crashes at the site in the past six years, which Mr Swain said was "very high" when compared to similar roadways.
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The reduction will result in a 16 second longer journey, Mr Swain said.
"In aggregate that's a big time loss, but to individuals it's very small," he said."What it tends to do is smooth out the traffic flow. We'll monitor how that road is operating as a consequence of the change and will fine tune the traffic lights as needed to maximize the flow of traffic."
Research showed even a 10km/h reduction in speed can leave a 25 per cent reduction in serious casualties.
Mr Swain said speed reduction doesn't always spot crashes but it reduce the severity.
"At the current rate I'd be very worried about a repeat of November 2018."
There are about 28,000 vehicle movements per day on the outlet. Mr Swain said consideration was given to the community's views provided during public consultation in May which about 560 people took part in.
"You very rarely get the community embracing speed reductions. I think we got 50 per cent opposed, about 40 per cent supportive and 10 per cent who were unclear. That's a reasonably strong evidence for a reduction," he said.
RACT executive general manager membership and community Stacey Pennicott said the RACT broadly supports the speed limit change.
The motoring body's submission asked the department to implement variable speed limit signage to limit reductions to specific times, and to do a communication strategy around the changes and implement a grace period for the motorists.
Following a review of the feedback, clear themes were identified throughout the submissions including poor driver behaviour, the need for better signage, additional lanes and or longer merging lanes, policing and enforcement of current speed limit and right lane rule, and support for variable speed limit signage.
The changes will come into effect next week when the new signs are installed next week.
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