I've personally 3 accidents in my lifetime caused by sudden changes to the speed on a highway, 2 of them came in the last few years since they released the new law that requires you to slow down to 40km/h if police are on the side of the road.
Admittedly, the rule itself isn't that bad, but as usual it was released with no consideration of the average Aussie driver. Unfortunately there are still people who drive in the right hand lane and then slam on their breaks when the flashing signs show a need speed limit. Had it go down from 110 to 70 the other day - the car in front didn't bother slowing down gradually, as soon as he saw the flashing sign he slammed his brakes to make sure he was under the speed limit right at the time he passed the sign. Needless to say there were about 6 cars that luckily escaped.
They really need to change this rule to allow leniency for drivers to slow down gradually. Cant expect someone to go from 110 to 70 in just a few metres on a highway.