By the 2010s, the M4 had 49 junctions. Junction 18 was located south-east of Chipping Sodbury and intersected with the A46. Junction 19 was located south-west of Chipping Sodbury. Junction 34 was located to the north-east of Cowbridge and north of Bonvilston. Junction 35 was located north-west of Cowbridge. Junction 36 was located north of Bridgend. Junction 37 was located between Pyle to the north and Porthcawl to the south. (TV: The Categories of Life) Junction 38 was located between Pyle and Port Talbot and intersected with the A48. (TV: The Categories of Life, PROSE: Bay of the Dead) Junction 47 was located to the north-east of Gorseinon. Junction 48 was east of Llanelli. The M4 terminated at junction 49, where it intersected with the A483 and the A48. (TV: The Categories of Life).
On her wedding day, 24 December 2007, Donna Noble got into a taxi which she hoped would take her back to the church, but instead it turned onto the M4 and headed along the Chiswick Flyover. The Tenth Doctor, in his TARDIS, was able to rescue her. (TV: The Runaway Bride).
Gwen Cooper drove along the M4 towards the Severn Bridge when on her way from Cardiff to East Grinstead to interview Clement McDonald in 2009. (TV: Children of Earth: Day One) The following day, Gwen and her husband Rhys travelled to London along the M4 in the back of a potato lorry. (TV: Children of Earth: Day Two).