I work as a Traffic Planner.
Basically, I plan out temporary road works and the speeds that traffic has to go through them. I don't make you all go 40km/h for the hell of it... There's a lot of QLD law and legislation and safety requirements behind that simple 40 speed limit. So keep at 40, you make the Traffic Controllers happy (and you don't want to piss them off. They will stop you for up to 15mins if you do), and you're making all the workers perform in a safer working environment