Key Points
- Location: Roundabout at the M4 Junction 32 (Coryton Interchange) extending over a distance of 1.54km.
- Period: Phased closures for 25 nights starting from Monday 7 September to Monday 12 October.
- Working Hours: The carriageway closures will operate overnight from 8:00pm to 6:00am.
- Access for Residential and Businesses: There are diversion routes planned, which include Merthyr Road and Oldfield Road through Tongwynlais in selected phases.
- Other Routes: A4054 Pendwylltal Road access from south will be diverted to Gabalfa Interchange during phase one.
- Longwood Drive Access: Longwood Drive access is available through most of the operation period except total prohibition for all vehicles except emergency vehicles during the sixth shift on Sunday 13 September.
Cardiff (Cardiff Daily) September 7, 2026 — Motorists travelling through the north of Cardiff are being advised to prepare for significant disruption as essential resurfacing work gets under way at the M4 Junction 32 Coryton Interchange. The comprehensive maintenance project covers a 1.54km section of the Coryton roundabout and is scheduled to be carried out over 25 nights, starting on Monday 7 September and concluding on Monday 12 October. To minimise daytime traffic congestion on one of South Wales’ busiest junctions, highway teams will enforce phased carriageway closures each night between 8:00 pm and 6:00 am. Local authorities have arranged dedicated diversion routes to preserve access for surrounding residential areas and commercial premises throughout the construction window.
How Will the Phased Closures Affect Local Traffic and Diversion Routes?
The resurfacing operation has been structured in distinct phases to prevent the complete shutdown of the arterial junction while ensuring contractor safety. Transport planners have designed targeted diversion routes to accommodate local residents and commercial traffic heading toward neighboring communities.
During phases two and three of the project, direct entry to Merthyr Road and Oldfield Road from the main interchange will be restricted. Motorists seeking to reach these locations will be directed to follow a designated diversion route operating through the village of Tongwynlais.
Additionally, adjustments will affect drivers approaching from the south during part of phase one. Access to the A4054 Pendwyallt Road from southern approach roads will be temporarily rerouted, with drivers required to navigate via the Gabalfa Interchange to reach their destinations.
What Are the Specific Access Restrictions for Longwood Drive?
Because no practical alternative public road network exists for Longwood Drive, transport engineers have prioritised maintaining open access to and from the street for the majority of the 25-night programme. Businesses and residents on Longwood Drive will be able to enter and exit during most operational shifts, albeit with potential minor delays as equipment moves through the zone.
However, a strict exception will take place during the sixth overnight shift, planned for Sunday 13 September. On this specific night, construction crews will be resurfacing the outer lanes of the roundabout directly across the junction with Longwood Drive.
Due to the heavy machinery and active layout of the resurfacing work across these lanes, general vehicular access will be completely suspended. Only emergency services will be permitted passage through this section for the duration of the shift.
Background of the Coryton Interchange Resurfacing Project
The Coryton Interchange, situated at Junction 32 of the M4 motorways, serves as the primary gateway connecting South Wales’ primary east-west motorway with the A470 trunk road heading north toward the Valleys and Merthyr Tydfil. As one of the most heavily trafficked roundabouts in the region, it handles tens of thousands of commuter, freight, and local vehicles daily.
Over time, heavy traffic volumes and harsh weather conditions contribute to wear and tear on the carriageway surface, leading to rutting, potholes, and diminished skid resistance. Scheduled maintenance programmes such as this 1.54km resurfacing scheme are vital to maintain structural road integrity, enhance surface grip, and prevent long-term safety hazards for high-speed traffic transitioning between motorway link roads and local arterial routes.
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What Does This Development Mean for Cardiff Commuters and Local Businesses?
The overnight closures at Junction 32 will directly impact evening commuters, commercial freight operators, and local residents who rely on the Coryton Interchange during night-time hours.
- Commuters and Night Workers: Drivers travelling between 8:00 pm and 6:00 am should anticipate increased travel times due to lower speed limits, single-lane restrictions, and detour routes via Tongwynlais and Gabalfa Interchange. Late-shift workers travelling between Cardiff city centre and the South Wales Valleys via the A470 are advised to plan alternative journeys in advance.
- Local Businesses and Logistics: Freight companies using the M4 and A470 corridor may experience minor logistical delays. Businesses located on Longwood Drive, Oldfield Road, and Merthyr Road must adjust late-night delivery schedules, particularly on Sunday 13 September, when access to Longwood Drive is restricted strictly to emergency services.
- Residents of Tongwynlais and Surrounding Areas: Local neighborhoods along the diversion routes are likely to see a temporary increase in overnight traffic volume, which may result in elevated ambient noise levels while work on the roundabout is active.
