:Rhondda by-pass

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File:B4278 passes under the Rheola Bridge, Porth - geograph.org.uk - 3590518.jpg on the by-pass at Porth]]

The Rhondda by-pass, also known as the Porth and Lower Rhondda Fach Relief Road,{{cite news|url=https://www.chandlerkbs.com/projects/porth-and-lower-rhondda-fach-relief-road|title=Porth and Lower Rhondda Fach Relief Road|work=ChandlerKBS|accessdate=13 June 2020}}{{cite news|url=https://www.rctcbc.gov.uk/EN/Resident/PlanningandBuildingControl/LocalDevelopmentPlans/LDPEvidenceBaseLibraryandAnnualMonitoringRe/RelateddocumentsEvidenceBase/EB87.pdf|title=Transportation Topic Paper|work=Rhondda Cynon Taf County Borough Council|accessdate=13 June 2020}} is a relief road running through the Rhondda, a valley in South Wales. It is built partly on the former Maerdy Branch of the Rhondda Line and a former branch line to Cymmer Colliery.

The road runs from Trehafod at the eastern edge of the Rhondda to Pontygwaith in the Rhondda Fach via Porth. The route includes the Rheola Bridge, which crosses near the point the Rhondda Fawr and Rhondda Fach divide. It opened in December 2006, and a plaque commemorating the road was unveiled by the First Minister for Wales, Rhodri Morgan, the following year.{{cite news|url=http://news.bbc.co.uk/1/hi/wales/south_east/6974274.stm|title=Morgan opens £98m Rhondda by-pass|work=BBC News|date=3 September 2007|accessdate=25 February 2017}} Local residents have complained about the noise on the road, as the imposing local geography of the Rhondda means it has to pass as close as {{convert|40|ft|m}} to residential streets.{{cite news|url=http://www.walesonline.co.uk/news/local-news/residents-angry-over-rheola-bridge-1922122|title=Residents angry over Rheola Bridge|work=Wales Online|date=8 April 2010|accessdate=25 February 2017}}