Wrong way lights

[VNA]

Then there's a "No Right Turn" sign on the left and two No Entry signs at the junction on the "wrong way" slip road, so there's certainly adequate signage for anyone who's paying attention.

Plus, the road markings.  Which would be my one suggestion – keep all the road markings on such motorway and dual carriageway junctions fresh.
I think the exit is standard width, and is that width so that articulated vehicles can exit with ease.  Yes the M9 is busy. 
Lets see how the trial goes…..