I’ve come up with a couple of routes around Miami.
The first takes in the downtown, weaving its way through the skyscrapers with a double crossing of the river and a brief glimpse of the Bayfront Park. THe streets are between 2 and 4 lanes wide but it does suffer from the typical American street circuit problem of 90 degree corners. Comes in at just shy of 3km.
The second has far more varied and flowing corners, and is set alongside the more famous Miami Beach. Trouble is the roads are narrow and it’s 0.5km too long, being 4000 meters in length. 3.5km is a really tough length to stick to! Anyway, it’s not eligible, but here it is anyway as I think it’s pretty interesting and follows a nice curvy road alongside one of the river/lake/lagoon things that Miami has