90 is pretty good traffic-wise. Actually, I have cycled them all.Traffic density is really reasonable. Avoid Orlando, US 1, and such main arteries where many cars come and go. Parts of highway 27 are Florida's suicide route in winter. Farther north 27 is good. Our Gov said FL is no longer the "dive or die state" for cyclists. Well, uhh, I think the Gov hasn't bike toured the state. The ST is fairly good for motorized traffic density. However, many cyclists get creamed here. In 20 years in my small town (16,000 people) eight people I knew have been killed on their bikes. I did not count the surviving injured. Maybe 20-25. The eight were people I had known to some extent in this town. Many others I did not know have been killed or injured. I have experienced such blatant negligent disregard of myrights as a cyclist by motorists it could be described as gross criminality. Even with many witnesses and police present nobody said a word as though it was acceptable behavior which it most certainly was not.
In short, your interaction with traffic will depend on where in particular you cycle.The ACA ST route is quite safe. Use it.