Average speed cameras are set to be installed on Rhuallt Hill between J30 and J28 and one in between at J29.
It comes after research found that more than half of drivers have been speeding on the stretch of road.
The radar collection system collected information from 394,326 vehicles and found that 217,642 had been travelling at speed in excess of 70mph on the westbound downhill carriageway.
Transport Secretary Ken Skates has said “Safety on our roads is an absolute priority and this latest data of vehicle speeds is clear proof why we are taking action on the A55 at Rhuallt Hill westbound.”
“The number of vehicles found to be travelling beyond the speed threshold on this part of the carriageway is of great concern and the measures we will now put in place will improve the safety of the travelling public, help cut the amount of collisions in the area and strengthen the resilience of the A55 .
“We must remember that road safety is a matter where we all have a part to play.”
Mr Skates also added “Collisions on the road can happen for a number of reasons, and excess speed is one of the most common causes.”
“The trial of average speed cameras in the area of the Rhuallt Hill is one of a number of interventions we are making following the A55 resilience study I commissioned last year and will help traffic flow in a safer environment.”
To reduce the amount of disruption caused, the cameras will be installed at night, with the system expected to be fully operational around mid-May, once they have been fully tested.