St John's Road in St Helier will be one-way for three months from the end of August.
The lower end of the road - between Parade Road and Cheapside - will become northbound only.
Temporary bollards will be installed to create more space for pedestrians
Motorists heading towards town (southbound) will be directed to use Tower Road and Westmount, unless their destination is on St John's Road.
Local traffic on St John's Road will be able to use Parade Road.
Infrastructure Minister Deputy Tom Binet says the trial will allow officials to gauge the impact of the change before he and the St Helier Roads Committee decide whether it should be permanent.
"The section of road near Cheapside is very narrow, as are the current pavements.
We hope that changes in layout at the Tower Road junction should mean that those coming from the top of the hill will reroute via Tower Road and Westmount.
We anticipate that traffic patterns on Parade Road will also change."
It is estimated the change will increase traffic on Westmount Road by 431 vehicles in the morning rush hour and 341 vehicles in the afternoons.
Plans for the trial will be on show at the Town Hall on Thursday (29 June) 5.30-6.30pm