Trucks will be banned from using the far-right lane on the Monash Freeway in a nine-month trial.
The restriction will apply in both directions, between Huntingdale in Mount Waverley and Jacksons Road in Noble Park.
The trial will determine whether the ban is to become permanent. It will begin on February 5.
Acting Premier Tim Pallas said the trial aimed to improve journey times and safety for all drivers.
He said the most common cause of crashes on the Monash Freeway involved lane changes and side swipes.
Heavy vehicles make about 40,000 trips on the freeway each day.
Mr Pallas said car drivers needed to allow trucks to do their job by making sure they could use the lanes available to them efficiently. He said truck drivers would also need to adjust to the new conditions.
"It will place a challenge on the trucking industry to adhere to these rules," he said.
VicRoads, police and cameras will enforce the rules but truck drivers who flout them will not be fined.
Roads Minister Luke Donnellan??? said there would be discussions with truck operators who continue to use the right-hand lane.
"There won't be fines; this is a trial," he said. "This is very much about trying to change driver behaviour both for trucks and drivers."
Trucks are already banned from using right-hand lanes on the Princes Highway from Geelong to Melbourne and on some parts of the Eastern Freeway.
Mr Donnellan said the Australian Road Research Board would evaluate the trial. He said the evaluation would consider the entire performance of the road under the trial, including safety and flow rates.
The Victorian Transport Association backed the trial. Its chief executive Peter Anderson said the higher concentration of trucks using the middle lanes meant car drivers would have to adjust their behaviour to keep the roads safe.
He urged motorists to remember that trucks needed greater stopping distances, refrain from excessive lane changing and "never cut off a heavy vehicle".