A third layer people forget about
The Greater Miami Expressway Agency (GMX, formerly known as MDX) owns and maintains Miami-Dade's tolled expressway system — SR 836 (Dolphin Expressway), SR 112 (Airport Expressway), SR 874 (Don Shula Expressway), SR 878 (Snapper Creek Expressway), and SR 924 (Gratigny Parkway).
That includes the land under and around those roads, not just the driving surface — the fenced strips beneath overpasses, embankments along the shoulder, and the areas between the expressway and the frontage road.
The example that trips people up
Large debris piled behind a fenced area under an underpass is a textbook GMX issue, not a city Public Works or county Solid Waste one — even though it looks like ordinary illegal dumping or storm debris. Sending it to the city first is why these reports so often bounce between departments before landing anywhere useful.
Quick check
If the issue is on, under, or immediately alongside one of the expressways above — especially anything behind expressway fencing — start with GMX instead of the city or county.