TechnicallyNotDeaf
Ugh. Accidentally copy/pasted wrong info above but I can't edit it. comment should have said:

Just before the Bunyip River crosses the Princes Highway (inbound), the speed limit used to change from 110km/hr down to 100km/hr but the road signs have been changed so it now drops to 80km/hr at that point. 

(The authorities changed this for safety reasons as some local traffic joins/crosses/leaves the highway at this point.)

This note is to mark the end of the 80 km/hr zone - here, it returns to the existing 100 km/hr limit.