Meh, shut the road till its safe.
Genuine curiosity...how do you bring cars to a stop from 100km/hr without leadup signage when you shut the road, compared to slowing them down to 40 or 25 ?
eFlares attached to cones if there's a bend in the road.
Otherwise, Mr/Ms Public should see the flashy/blinky lights on the big truck(s) from a goodly distance.
General rule of thumb is to give the punters four seconds to wake up and do something.
I've seen something, somewhere that says if the speed limit is 100 km/h, set your first sign 150 metres away (i.e. 1.5 times the speed limit in metres). Seems pretty reasonable.
Advice I give people new to traffic control, "Always assume the public are drunk/stupid/homicidal and have at least two escape routes."
As OIC, if I don't like the scene, the road gets closed.
Safety of my crew is more important.