The £13m design and build project, which is funded by Transport Grant from the Welsh Assembly Government, will improve access to one of the largest industrial estates in Wales, with more than 300 companies providing in excess of 7,000 jobs.
Work on design will commence immediately, with construction works due to start in May.
The existing highway access is gained via unclassified roads and suffers from congestion, particularly at peak times.
The new northern access comprises 3.2km of new two-lane dual carriageway with three at grade roundabout junctions and a new bridge.
At the southern access, 1.2km of new single carriageway road will be constructed, with three new or enlarged junctions.
This part of the scheme includes a new bridge over the River Clywedog, scour protection retaining walls, two culverts and a sheet piled flood protection barrier.