The Brynglas Tunnels carry the M4 motorway under Brynglas Hill in Newport. The 1,200 ft-long twin-bored tunnels were the first tunnels in the British motorway network and are still the only bored tunnels.
The tunnels and adjacent Usk bridge were originally planned by Newport Corporation in August 1959 in a plan submitted to the Ministry of Transport. Work started on 10 September 1962 and both structures were complete and open to traffic during the first week in May 1967.
Almost as soon as the M4 Newport bypass (junctions 24-28) had opened, the traffic levels had grown to such a degree that the road had to be widened to three lanes in each direction. This was finished in 1982 but with the exception of the tunnels and Usk bridge which remained as dual two-lane sections. During the original construction several houses on Brynglas Road (where the modern Newport Lodge Hotel now stands) had to be demolished due to structural weaknesses caused by the tunnelling. Therefore the technical challenges and risk associated with widening the existing tunnels in a highly built-up area were found to be too great. The tunnels remain a bottleneck on the motorway and as of 2004 an entirely new bypass south of the city has been proposed.