Llangyfelach Interchange

The Llangyfelach Interchange, junction 46 of the M4, was built over a period of about 30 years between 1972 and the mid 2000s. Prior to 1972 the junction was a simple T-junction, with the B4489 descending a rather steep hill to the A48, which was the main east-west trunk road of its day.

The junction was selected as the western terminus of the M4 Morriston Bypass (known during development stages as the A48(M)) and to accommodate the new motorway, a new roundabout was built. The roundabout is essentially the main roundabout that exists today, except that both carriageways of the M4 tied into the roundabout at the point where the westbound off-slip does now, the westbound off-slip being a remnant of the westbound carriageway.

In 1977, the M4 was extended west to bypass Pontarddulais. To achieve this, a new eastbound slip road was built from the roundabout, bridging over the line of the new motorway, and rejoining the eastbound carriageway. This enabled the original eastbound carriageway and the westbound carriageway to be re-modelled to form a limited-access junction with the extended motorway. West-facing slips were not provided at this stage as this movement was accommodated at the Penllergaer Interchange to the west.

North-west of the interchange lies the former Felindre Steelworks site, accessed from a T-junction west of the Llangyfelach interchange. When this site was redeveloped it was deemed necessary to provide west-facing slips at Llangyfelach as well as a direct link to the development site. A second bridge was built to the east of the 1977 bridge, and at a slightly higher level in order to provide adequate forward visibility onto the main roundabout. The two bridges were linked at the northern end by a half roundabout arrangement which turns the two bridges into a "longabout". The link to the development site was built here, the eastbound on-slip was modified to suit the new arrangement, and a new eastbound off-slip built to link from the M4 main line. The westbound on-slip was built from the original roundabout to the main carriageway.

Routes

Route	To	Notes
M4	Caerfyrddin / Carmarthen	For A4138 Llanelli
M4	Caerdydd / Cardiff	Formerly A48(M) For A465 Castell-nedd / Neath
A48	Amlosgfa Treforys / Morriston Crematorium, D.V.L.A, Treforys / Morriston	For Ysbyty Treforys / Morriston Hospital
A48	Parc Busnes Penllergaer / Penllergaer Business Park	For Bryntywod, Afon Tinplate, and A483 Abertawe / Swansea
B4489	Llangyfelach
B4489	Parcio a Rhannu / Park and Share, Felindre