Sun or shade? Either way, think about that low growing yellow lantana that's everywhere. It will grow with no additional water at all and when it does rain, won't mind being swamped for a while. The traffic won't bother it either.

Ajuga would do nicely if it's sort of shady.

In addition to the above suggestion, I think some thing small that can thrive on it's own like a succulent may be in order. Sedum comes to mind as one that may work, many mini varieties that grow very low so will not obstruct the view of traffic. I read that the genus ranges from frost tender to frost hardy. Bold to beautiful. A few are tall yet many are small and delightful.

Ankrara's Hobby Corner

If it's a sunny area, for something really low growing, but spreading, try portulaca aka moss rose. Great drought tolerant plant that blooms all the time and reseeds itself readily.

Jeanni

I was going to suggest moss roses! I had some volunteer in my yard and I love it! great low-maintenance stuff... (how does one spell maintenance anyway??)

Can anyone suggest a sedum that grows well in Savannah?

Asian Jasmine!

I have some Portulaca and it grows great, just to break up the "mass", I have some society garlic, it has stalks with pretty purple flowers on it. Among that, you can plant some Coleus, they are easy to control too. I see alot of people planting Coleus aroung mail boxes, etc... They don't need a lot of care, although you might need to sprinkle them with a little water if it gets too dry.

I have a mailbox garden like what you describe, and I have daylilies, crocosmia, achillea, Milkweed, Kniphofia and brown-eyed susan vines. Very low maintenance. I hardly ever do anything out there and it always looks great!

Moss verbena should do good there as well. It will grow in the cracks of asphalt and concrete. Doesn't like to be watered and blooms profusely if neglected. But a flood of water won't effect it either. Perfers sun but shade won't bother it. Doesn't mind foot traffic and grows low so a site problem wouldn't be an issue.

Heck, I have it filling about an 18 X 4' area of CONCRETE. It grows out of a half-inch crack where I jammed a stem of it some months ago; I stuck some good soil in after it and since then it has survived on canine effluence and air plus runoff from my other plants. Inexplicably, one I had in a pot formed several tubers and inside the tubers (one broke when I pulle it out of the pot) was WHITE. So you have a black-purple leaf and a white tuber.
But it does not die (at least in Zone 9.)

What did you decide on and how did it work out?
I'm planning my own curb planting now.