This project, delivered under the North Wales Trunk Road Agency Framework, involved the realignment of 650m of trunk road within Snowdonia National Park to improve alignment, ensure the stability of the A470 and remove a bottleneck on the strategic highway network.
The new carriageway was constructed along the existing A470, a key transport link providing a route for local, commercial and tourist traffic. The work consisted of major rock excavation of the land adjacent to the existing road, forming a stable embankment and slope and constructing a new road, including flexible pavement, associated drainage works, service installation, landscaping and fencing.
Where available, works were constructed offline with traffic remaining on the existing A470. Upon completion of the new northbound carriageway, the traffic was switched under extensive traffic management from the existing trunk road to the new carriageway. This allowed the necessary structural fill to be placed over the existing road to facilitate construction of the new southbound carriageway embankment. Localised traffic management was required to complete additional works such as drainage, service installation and finally finishing works prior to removing the traffic management to allow traffic to run on both lanes.
During the early contractor involvement stage we steered design improvements and Value Engineering to deliver more than £200k (10%) of savings, including delivery of a more efficient drainage scheme and redesign of the rock slopes to eliminate retaining walls and reduce visual impacts. We also improved designs for resident accesses. All 100,000 tonnes of rock cuttings were recycled and reused on the scheme, by the local forestry commission and farmers.
The project was located is within Snowdonia National Park, and included several designated and candidate Special Areas of Conservation (SAC/cSAC) and Sites of Special Scientific Interest (SSSI). Tree protection, bat, badger and newts were all addressed in the project and regular monitoring was essential. Good environmental management in line with a strict plan and close liaison with the Environment Agency was essential to the success of this project.