M1 motorway closed after serious accident near Watford The M1 is closed in both directions near Watford in Hertfordshire after a serious accident. The southbound carriageway is closed between junctions five and four and is not expected to re-open until mid-morning at the earliest. The northbound carriageway of the motorway is closed between junctions one and two but is expected to re-open by 07:00 GMT. The link road from the A41 westbound to the M1 northbound is also closed. Drivers are advised to use the A1, A40 or M40.