In article , Roland Perry
writes
The only disruption will come at the end, when the traffic is diverted to
the new route. My guess is that the northbound traffic will be moved first,
with a few weeks of lane 1 closures required while they connect the new to
the old carriageways, then an overnight closure for the final switch to be
made. The same procedure would then be followed a few months later to
divert the southbound carriageway to the new alignment.

The amount of work you would be expecting them to do "overnight" beggars
belief.

I disagree.

Build the two new carriageways. At each end, cut them off very close to
the edge of northbound lane 1 (there's no hard shoulder, right? if there
is, adjust description accordingly).

Cone off northbound lane 1. Spend a week or two filling in the narrow
gap between the old and new northbounds at each end.

Not sure that you even need a closure to switch over. Simply move all
the cones.

Repeat for the southbound (though this time you're closing lane 4).

--
Clive D.W. Feather