Mae Ymchwiliad Cyhoeddus yn cael ei gynnal ar hyn o bryd i weld ai Prosiect yr M4, ar y cyd â Metro Dinas-ranbarth Caerdydd, yw'r ateb cynaliadwy a hirdymor i'r problemau difrifol − sy'n prysur waethygu − ar yr M4 o amgylch Casnewydd.
A public inquiry is ongoing to scrutinise whether the M4 Project, in collaboration with the Cardiff City Region Metro, is the long-term, sustainable solution to the serious and worsening problems associated with the M4 around Newport.