South Florida IS too big to evacuate as you are seeing.
The real problem in Houston (I live here) is that the storm went from tropical depression to category 3 on the beach in literally 3 days. I first learned that it was something to be concerned about on Tuesday morning. It hit us Friday night.
South Florida has at least had a few days warning here.
But the fundamental problem in Florida is that there is only one escape route (due North) and it is hundreds of miles long. I have friends and family in Florida and everyone has the same fear - getting stuck in traffic, running out of gas or having no place to stay near Orlando and then having the storm overtake them. Most people seem to think that the best bet is hunkering down at home with food and water nearby and hoping for the best.
Looks like FL is doing pretty well to me, and they haven’t even enacted contraflow yet. I’m sure there are ways to improve, but it looks OK to my mind.
Yes, that can't be said enough. People who are 20 or more miles inland should be sheltering in a sturdy home or a local shelter. 10-20 miles can use their judgment. Anyone in Florida with a mobile home needs to look for a local shelter. But the idea that everyone inland in Florida needs to go north is incorrect.
I don't know the population density around Miami and along the coast (say 10 miles). I suppose it's pretty high and that's a problem
But on the flip side the NHC predicts cat 4 with two caveats. Both caveats will make Irma less than cat 4. The 20-30 mile (inland) destruction zone for Andrew and for Camille will be smaller for Irma.
There are going to be a lot of people on that peninsula hunkered down and riding out the storm.