|Length:||13.8 miles (22.2 km)|
|Met:||A487, B4343, A44|
|Now part of:||A4120|
|Route outline (key)|
It ran along the left bank of the Rheidol east from Aberystwyth via Devil's Bridge, to join the A44 at Ponterwyd (where that road crosses the Rheidol).
The road quickly became upgraded to Class I status, becoming the A4120 in the mid-1920s. It remains this number.