Yr unig eithriad yw'r M4 yng Nghasnewydd, lle y nodwyd mai gosod terfyn cyflymder o 50mya drwy'r system terfyn cyflymder newidiol, mewn cyfuniad â gwyriadau amrywiol posibl oedd y camau mwyaf priodol.
The one exception is the M4 at Newport, where the setting of a maximum 50mph speed limit via the variable speed limit (VSL) system in combination with potential variable diversions were identified as the most appropriate measures.