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photograph of the bypass

We have built a bypass from the Goat roundabout on the A499/A487 junction to the Plas Menai roundabout, around Llanwnda, Dinas, Bontnewydd and Caernarfon.

Region / County:
north Wales
Start date:
early 2019
End date:
early 2022
£139 million
First published:
14 September 2017
Last updated:


Why we did it

We wanted to: 

  • make it easier to travel without traffic jams
  • make it easier to travel between Llyn Peninsula, Porthmadog, Bangor and the A55
  • reduce noise and air pollution for people who live along the A487
  • make it safer for people to travel between towns
  • make it easier for heavy goods vehicles to travel in the area
  • make it safer to travel between Caernarfon, Bontnewydd by walking and cycling.

We wanted to prevent:

  • longer queues at the A499/A487 Goat roundabout
  • high volumes of vehicles passing through towns along this route
  • queues and delays on the A487, particularly at Eagles Junction, St David's and Morrisons roundabouts in Caernarfon, and at Plas Bereton.

What we did

We have:

  • completed 9.8km of new road between the Goat roundabout (A499/A487 junction) and Plas Menai Roundabout linking the bypass with the A499 and A487 Felinheli bypass
  • built 17 new structures including:
    • 2 viaducts, over the Afon Seiont and Afon Gwyfrai
    • 3 overbridge structures carrying local side roads over the bypass
    • 12 underbridge structures (including a crossing over the Welsh Highland Railway)
  • put in 25 new culverts for water and animal crossings
  • changed both the Plas Menai and Goat and 14 existing local side roads
  • built a safe crossing for cyclists, pedestrians and equestrians at the Goat roundabout to provide continuity with Lon Eifion and A487 Bontnewydd
  • built a walking and cycling route linking where the bypass crosses Bethel Road with a route to/from Bethel

The route has:

  • created a western bypass to Llanwnda, Dinas and Bontnewydd
  • crossed the existing A487 south of Caernarfon
  • crossed Afon Seiont
  • passed south of the Cibyn industrial estate to form a junction with the A4086
  • crossed the B4366.

It has involved constructing 22 structures including culverts and 7 bridges. The bridges are:

  • a crossing over the Welsh Highland Railway
  • a 300m viaduct over Afon Seiont
  • a 280m viaduct over Afon Gwyrfai and its flood plains
  • 4 bridges carrying existing roads under or over the new road.

We also made space for wildlife and biodiversity along the road. This included:

  • creating burrowing and foraging habitats for water voles
  • putting in a number of culverts to allow bats, fish and otters to cross the road
  • installing swift and dipper boxes on the two main viaducts
  • creating soft verges under one of the viaducts to allow wildlife to pass
  • installing amphibian-friendly drainage into road gullies
  • using a local seed source to plant flowers along the verges.

The project supported local businesses and employed local people. About £70 million was been spent on Welsh businesses, £12 million of this on small to medium enterprises. The construction workforce spent about £2 million on local shops, businesses and services.

We will also improve the existing A487 to improve existing junctions.

We have also worked with Gwynedd County Council to make the existing A487 through Caernarfon and Bontnewydd into a county road.

The brochure and more detail about the project can be found under the publications section of this page.

Aerial video of the works to build the Caernarfon to Bontnewydd bypass


Public consultation exercise: 2010 to 2011
Preferred route announced: spring 2013
Appointment of contractor: end 2014
Site investigation and surveys: throughout 2015
Preliminary design: end 2015
Orders exhibition: autumn 2016
Public local inquiry: summer 2017
Start of bypass construction: early 2019
Bypass opening: early 2022

How we consulted

Four bypass options were presented to the public as part of a consultation exhibition in March 2010. 972 people attended these exhibitions and 498 completed questionnaires were received.                                         

The responses from these questionnaires demonstrated that the public was in favour of the bypass. Further consultations took place towards the end of the year before we announced our preferred route.

We had meetings with landowners, businesses and residents to understand the impacts of the scheme.

Latest announcements

Announcements and notifications


Reports, environmental statements and plans


The legislation required for the project to proceed including drafts for public comment

Help and support

Ask a question about the project or report an issue

You can claim from the 18 February 2023 to 18 February 2029 for land depreciation as a result of this project.

Find out more

Balfour Beatty Jones Brothers (Ruthin) have a site office on Seiont Mill Road, Caernarfon LL55 2YL, open during normal business hours.

For appointments you can contact the Public Liaison Officer, on 07786 513571 or