The tunnels and adjacent M4 motorway Usk bridge were originally planned by Newport Corporation in August 1959 in a plan submitted to the Ministry of Transport. Work started on the £3m tunnels project - led by engineer Sir Owen Williams on 10 September 1962. Both structures were complete and open to traffic on 5 May 1967. During the 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 and prompting questions in the House of Commons.
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 (Junctions 25-26).
M4 sliproads at Junction 25 (Caerleon Road) are diverted to reduce traffic through the tunnels. M4 Westbound traffic joining at Junction 25 is diverted via Junction 25A/A4042 (Heidenheim Drive)/A4051 (Malpas Road) to Junction 26. Similarly eastbound traffic wishing to exit at Junction 25 is diverted from Junction 26 via the A4051/A4042/Junction 25A. This adds to congestion on Malpas Road and other local roads near Newport city centre at peak times.
A new M4 relief road south of Newport was proposed, but on 15 July 2009 the scheme was dropped by the National Assembly for Wales. Hence the A48 Southern Distributor Road, a two-lane dual carriageway connecting M4 junction 24 to junction 28, remains the alternative route.