A bylaw banning private vehicle sales on state highways will be used to stop people marketing their cars on State Highway 87's southern entrance to Mosgiel.
Vehicles breaching the bylaw can be towed and stored at the owner's cost, and would-be sellers could be fined $500.
New Zealand Transport Agency (NZTA) area manager Roger Bailey confirmed vehicle owners would be warned before more serious measures were imposed.
A letter would be placed on windscreens, asking the owner to remove their vehicle immediately.
Registrations would be noted.
After that, any vehicle registered to the owner found for sale there - or beside any other state highway - would be towed.
Mr Bailey said roadside sales and marketing was an ongoing and steadily worsening problem beside the road into Mosgiel.
It was increasingly a safety concern as more people inspecting roadside vehicles put themselves in harm's way on the busy highway.
The vehicles could block visibility from entrances and intersections, and cut the amount of road available for cyclists.
They also hindered legitimate day-time parking for residents, businesses and visitors, Mr Bailey said.
Warning signs would be erected over the next few months and no-stopping lines might be used to ensure safer access at some driveways.
