|Length:||13.4 miles (21.6 km)|
|Met (1964):||A4059, B4512, A4058, B4278, A4119|
|Now part of:||A4233|
|Route outline (key)|
The B4277 was a medium-length B-road in north Glamorgan.
The road originally ran down the valley of the Rhondda-fach from the mining community of Maerdy (where it was the only classified road) to Porth on the A4058. At the start of the 1930s the previously unclassified track running north across the mountain from Maerdy to Aberdare in the Cynon Valley was improved as part of an unemployment relief scheme and added to this route.
The 1935 Road numbering revision saw a further, southward extension when the section of the B4278 between Porth and Tonyrefail – although not that between Porth and Penygraig – was added to the B4277.
Today, most of this route is the A4233, although quite a bit of the original urban route is now bypassed.