Interplanting different shrubs is a good idea... maybe you might consider wax myrtle! Its drought and flood tolerant, native, gets tall, and suckers so you always have growth filling in the gaps. Its also very dense, responds well to pruning, and even smells great when you trim it or rub the foliage. Another idea that would be awesome is shell ginger. The non variegated kind gets taller, but they both make a very dense grove that will be hardy where you live. The flowers are beautiful as well. Both of these solutions are pretty fast growing. Good luck!

Wax myrtle can be slow growing and somewhat thin until well established - many years from now .
Shell ginger reaches 8 feet - at the most and dies back with every freeze .

Have you considered regular Walter Viburnum - not the dwarf variety ?
"Walter viburnum, in the opinion of some nursery growers, is the very best viburnum for use in central and south Florida.

Walter viburnum will grow well in a site that receives full sun or shade. It is native to acidic wetland forests that are frequently inundated for a period of time during the year, but it tolerates a broad range of growing conditions including moderate drought.

No pests or diseases are of major concern. "

This link says it also attracts butterflies .

My neighbor has a hedge of this and it is absolutely gorgeous - thick and dense and the tiny white flowers are covered in butterflies . He does does baby it with lots of water and fertilizer but will do fine on it's own - just not as quickly . Regular WV can get to be 25 feet tall .

Here is a link that might be useful: Viburnum obovatum Walter Viburnum, Blackhaw

Wax Myrtle is a creeper. I have had a bush for 2 years and still has not come close to 5 foot. Firebush grows like wild fire and is thick if getting full sun. A small firebush will be 5-6 foot in a year. In 2 years 10 foot. Grows 10-12 foot.

I like some of the other suggestions, maybe a mix of stuff. If you cannot stand the road, one type of beetle or fly wipes all similar plants out and there the road is again (or hurricane). Like ficus's getting devastated by white fly right now.

Thicker leaves plants are better for noise where I think thinner leaves better for opacity.

Ever think of tree's? Green or silver buttonwood grow relatively fast and are native. They get about 15 foot wide. 6 or 7 of those and maybe a front line of another bush, coco-plum (native medium speed grower (10-15 foot)) or firebush.

Does the wall side of your yard catch the morning or afternoon sun?

7 Tree's $150 a piece (at bulk)
36 Firebush 7 gallon around $250.00. (3 foot apart)
55 Cocoplum 7 gallon around $390.00. (2 foot apart)

Your looking at $1,500 far better then $5,000. If you were expecting the sting of $5,000, great, make it $2,000 and let someone else do the install! Sit back relax and enjoy some coffee.

Problems:
I think firebush might drop leaves in orlando cold weather. I would check that.

Take a look at this book for idea's.
http://www.swfwmd.state.fl.us/publications/files/waterwise_landscapes.pdf

Has allot of Florida and non-invasive plants to help with xeriscaping

Go check out some of the gulf courses and nicer private communities in orlando and see what tall tree's they are using / bushes to block out roads.

How about silverthorn bushes (Elaeagnus pungens). They are very fast growers and get quite dense. Contrary to the name they don't have thorns.
Another possibility is lorepetulum which is also a fast grower that has unusual looking pink flowers.

The least expensive and fastest growing solution is to use Areca palms. You can buy them in quantity from any nursery in your area. For 110' you'll want 15 of them in 7-gallon cans. Plant them on 8' centers and don't ever prune them! They will go in the ground at six feet tall and double that in two years. When they bloom and the seeds drop, cover them with a thin layer of topsoil and mulch and they will all sprout and fill in any blank spots. If you plant them now, by next Spring you will have your inpervious hedge.

Wax Myrtles have done great for me. There are some dwarf forms available, but most are not. Mine grew very fast and are 10' tall. They take flood or drought as stated, and berries for birds. White or Spanish stoppers are nice, native, provide berries for birds. How about Red Cedar trees if you don't care if they get big? Firebush can be killed to the ground if you get freezing weather.

Gary

How about bottlebrush? Lovely red "flowers" and a bonus - hummers will be drawn to it.

If you like the look of bamboo I have a suggestion that's easier to control and is an even thicker screen. It's called Tiger Grass. It's beautiful, and multiplies but doesn't send out runners. I'm using it for a screen by my swimming pool. Everyone who sees it comments on how pretty it is. (I don't have a picture of it I can post right now but if you are interested let me know and I'll post one later from home.)

I bought mine at a Leu Gardens sale a couple years ago so I haven't shopped for it locally, but I've attached a link to a recent discussion we had about it. A couple people found it on e bay, internet sellers and local nurseries.

Kate

Here is a link that might be useful: Tiger Grass discussion (Feb 09)

Mexican Sunflower aka tithonia. Seriously it will easily grow thick enough to block all sight of the road and hopefully some of the noise too. In zone 10 it can reach 10 or 12 feet in a season or two, not sure if it grows as fast in zone 9.

I have Tithonia as a road block against a divided four lane highway .
It grows to 20 feet and looks gorgeous when it blooms .
In zone 9 it must be cut back to the ground in January/February .
Takes another couple of months to return to full force .
I love mine and get a ton of compliments when it is blooming in the Fall .
I would NOT recommend this as a permanent road block for hedgeasap .
I still vote for full grown Walter Viburnum .

It will grow that tall here, at least by the second season. Mine is taller than the house right now but it's in a very protected spot. The problem in z9 is that a frost will make it drop all it's leaves. So mine is tall, but mostly leafless, although it's coming back quickly. Even if the stalk dies it will come back from the roots, but it can be really ugly while it's recovering.

Afraid Id have to put up a cement wall first LOL