Live updates as crash brings traffic on the M4 and A48(M) to a crawl The incident is causing delays on the motorway and there are also a number of train cancellations (Image: Google Maps) A crash on a junction leading to the M4 is causing long delays between Cardiff and Newport and a number of train cancellations is causing disruption on the railways The A48(M) between Cardiff and Newport is partially blocked northbound, with traffic very slow due to the crash on J29 of the M4. One lane of two is partially blocked heading onto the M4 off the A48.