The M27 motorway will be closed completely in both directions between Junctions 9 (Whiteley) and 11 (Fareham), from 8pm, 24 December 2025 to 4am on Sunday 4 January 2026.

The closure is required to put in place a new four-lane wide underpass beneath the M27, using a ‘box slide’ engineering technique. Using this method means that many months of lane restrictions, speed limits, and overnight works can be avoided.

The giant pre-constructed concrete structure – weighing approximately 8,500 tonnes – will be slid 65 metres into a deep trench cut into the motorway embankment, from its current construction location on the north of the motorway. The motorway will then be fully reconstructed above it.

Before the sliding operation, 24,000 cubic metres of material – which could fill around 10 Olympic size swimming pools – will be excavated from the existing embankment to accommodate the new underpass, before the M27 above is reconstructed and reopened to traffic.

The underpass will provide two traffic lanes in each direction connecting with new westbound entry and exit slip roads and a new eastbound exit slip road. It will also accommodate a shared footway/cycling route connecting with Fareham Common to the south, and the Welborne Garden Village development to the north.

An animation of the box slide is here:

(Picture – Hampshire CC)