O 4 Hydref ymlaen, mae Llywodraeth Cymru wedi rhybuddio y gallai modurwyr sy'n gyrru’n gyflymach na'r terfynau cyflymder 50mya ar rai o'r ffyrdd mwyaf llygredig yng Nghymru gael llythyr neu ddirwy drwy’r post.
From 4 October, motorists exceeding the 50mph speed limits on some of the most polluted roads in Wales could receive a letter or fine through their doors, the Welsh Government has warned.