We discussed this at the Shed yesterday, and also spoke about slowing down for flashing lights on workers trucks on the opposite side of the road. If there is a median strip/plantation between the opposing lanes, it is not necessary to slow down if the lights are on the opposite side. If there is no median strip, vehicles travelling in both directions must slow down.
My daughter told me this afternoon that a tradie who works on those sites told her and the other school crossing supervisors on her corner that those trucks are being fitted with speed cameras to catch drivers who don't slow to 40 kph in the marked zones. They reckon they'll catch hundreds.