Motorway lane allocation sign
A blue sign with a diagram showing the left lane exiting and two others continuing, and the following text.
Left lane destinations: Port Talbot; A48.
Right-hand two lanes destinations: Abertawe; Swansea; M4.
Junction number: 38.
The third lane departs here, and for the most part the M4 will now have just two lanes for most of the rest of its journey.