I regularly call Vic Roads... usually about traffic sensors that don't detect bikes (ever been stuck at a light that doesn't change?)... and they usually have a crew out to fix it them within a week.
Fixing a sensor often requires cutting new loops in the road... so it's not a minor thing (but not horrendously expensive either).
I deal with them regularly and have found them overall to be the most responsive of all the government entities I deal with.
Vic Roads are expert managers of risk and have an appreciation of consequences that is unusual in a government entity... so if it's likely to get them sued, create a future liability or get the minister on their back they will do something about it.
Writing a letter setting out the problem is often a good way to get their attention... as then the problem is clearly documented and may be used against them in a court of law.
If you can figure out how to fix the problem even better... then they can't say they didn't understand.
I do most of this by email then you're not wasting time on the phone and everything is clearly documented.
Just ring them and find out who the responsible person is and then follow through with that person until the problem is resolved.
Their managers seem to keep an eye on things (unlike many government departments) so issues don't simply get ignored: try to avoid staff who don't action issues.
Vic Roads has a higher than average IQ for an organisation... and that probably helps get problems resolved rather than just shuffled around.
Vic Roads also seem to be the most open to constructive dialogue (although they will stone wall you on some issues). Mostly staff also have a good technical knowledge which makes such a dialogue possible.
Mostly it seems that the squeaky wheel does get the oil.