You certainly have done a lot of research on the noise problem, but it’s not clear to me what you are expecting to be done, and by whom.
So far a I’m aware the purpose of the Legislation is to provide building design / construction guidelines to permit the habitable areas of new residential developments (and others) to meet target noise levels given their proximity to certain noise sources, such as arterial roads in your case.
I’m not familiar with all the provisions of the Legislation that you’ve referenced, but I know that such provisions are generally reflected at the development planning level by a State Environmental Planning Policy (SEPP) and at the development consent level by a Local Environment Plan (LEP).
Based on your research, your building’s compliance with the Local Council’s LEP with regard to road noise impacts upon habitable areas was met by way of a private certification prior to the sale and occupation of the Units therein, so that is as they say “it”.
If traffic movements on the nearby arterial roadway have increased or if the original assessments were in error such that you and a few other residents are now adversely affected, I don’t expect that either the Council or NSW Roads & Maritime Services will do anything at this stage to ameliorate those impacts; and really you shouldn’t expect them to.
So what’s the solution?
Well the external windows of the building are almost always Common Property (unless they’re facing a balcony or similar area that’s part of the “Lot”), and therefore the Owners Corporation (O/C) is responsible for the maintenance and repair of those.
So IF you’re an Owner your best option would be to speak with the Secretary of your Executive Committee or the Strata Manager about whether the windows of concern are Common Property, and if they are, about the possibility of then including a suitably worded Motion on the Agenda of the next General Meeting of the O/C to consider that fitting double-glazed windows (at some locations) or the retrofitting of a membrane to some existing windows are indeed maintenance items.
If they go for it, maybe have your window/s “maintained” by the method preferred by those at the General Meeting in the first instance to assess the results.
If the windows of concern aren’t Common Property or if the O/C doesn’t consider that insulating those is a maintenance issue, then you would need to seek the O’C’s consent to undertake those works yourself, and perhaps ask (nicely) for a O/C contribution.
If you’re a tenant and the noise levels are really that bad, then I’d be looking to terminate your Lease on the basis that the Unit’s not habitable.
I guess that covers all the options; good luck.