Interstate “Candy Canes”?

Although I’ve traveled through a good chunk of the United States, most of that has been through the air. I haven’t really driven all that much outside Georgia, Florida and the Carolinas.

This may be a regional thing here in this part of the world… but for years I noticed these weird “candy canes” on the side of interstates here in the South.

• They’re made out of metal, and look to be about the same diameter as dryer duct.
• They’re always painted the same shade of green as the electrical or telephone boxes you sometimes see on the edge of people’s yards, although they’ve usually been sitting there so long that they’ve beached to a milky green shade.
• They appear to be slightly larger than a mailbox.
• They are usually located well off the road, as if they’re not for public use. In other words, they don’t appear to be covering up one of those call boxes you used to see on side of the road, for instance.
• The “hook” of the cane always points towards the road, never away from it.
• I’ve never seen any writing on one, and I feel they’re too common and too uniform in appearance to be some weird “Jesus Saves” kind of thing.

Are there any civil engineers out there who know what those things are? When I was a teen, I thought they might be venting some type of gas, but they seemed too numerous for that, and why have the hook facing the interstate? As I got older, I wondered if they were capturing some type of air quality data, but then… why the “candy cane” form factor?

Having said all that, I don’t think I’ve actually seen one in a while. At any rate, this is one of those things I’ve googlefailed at for years, and it’s really been bugging me. Anyone who could answer this would be my hero or heroine!