|Length:||18.2 miles (29.3 km)|
|Meets:||A48, B4591, A4051, M4, B4596, B4236, B4051, A472, B4269, A40, A465|
|Former Number(s):||A472, A4125|
|Old route now:||A4051|
|Route outline (key)|
The A4042 is an important north-south road in Monmouthshire.
The route begins at a light-controlled junction with the A48 Southern Distributor Road in the south of Newport and travels northwards as Usk Way through the city's docklands. It continues as Kingsway in the city centre and then becomes an elevated roadway known as Heidenheim Drive through the Crindau district. Here the road meets the M4 and J25A, with a spur running alongside the motorway to J25. The A4042 gains primary status from here and continues north as a dual-carriageway road with the occasional roundabout.
The road bypasses Cwmbrân to reach the A472 at Pontypool. It is now the dominant number in a multiplex east until that road turns off at the end of the dual carriageway at Little Mill. The A4042 now becomes a winding single carriageway through a few small villages. Eventually it crosses the River Usk which it ran alongside back in Newport, before ending at a roundabout to the south of Abergavenny, where it meets the A40 and A465.
In 1922 the A4042 ran only from Newport to Pontypool. It still follows this route although it has been heavily bypassed and very little is on its original route.
The southern end of the A4042 was on the A48 in the centre of Newport. It then headed north along what is now the A4051 until the end of the dual-carriageway section. A few villages later, it ended on the A472 in Pontypool.
The A4042 was extended north to Abergavenny in 1935 along what was the A4125, although this required a multiplex with the A472. It became the dominant partner in the multiplex when it was deemed the main route, at a similar time to the building of the Cwmbrân Bypass.
At the southern end, the A4042 was extended south of the A48 along what was the A4052 to just past Newport Transporter Bridge. This section was declassified with the building of the current Usk Way, the road's present southern end.