Why do highway department put up "Guardrail Damage Ahead" signs?

Same reason McDonald’s has to warn consumers that their coffee is hot.

Law Suits.

Excellent question.
They’re saying “Don’t plan your accident here. Move on down the road.”

If you pull off the road onto the shoulder, and are counting on the guardrail being there to guide how far you can go to the side, a gap could mislead you down an embankment or set you up to gore your car on the rail where it starts up again.

Why does each good rail not have a sign that says “Good,
Usable Guardrail Ahead”?
Because people are both stupid and greedy; to run into a fully working and functional guardrail there is no money in it, and supposedly it will do what it is supposed to. To run into a guardrail that is busted may not, so if you lose control you had best try to use something else to stop you because if you use that one you can end up down a ravine and be injured more. Not to be told that fact is certainly someone else’s fault, and some greedy whore lawyer will help you find someone, anyone, so as long as they have deep pockets and want to settle out of court.

@dabbler Many roads have no guard rails at all. Rely on your senses and experience to not put yourself down an embankment. Similarly, we have warning signs here that say “Soft Shoulder” (so you may not be able to pull your rear wheel drive Miata out of the gravel).
Somebody who claims their accident was worsened by lack of signage, I don’t mind having out of the driving pool.

Apparently, it’s regional as I’ve never seen such a sign here in the Midwest.

I agree that it’s likely lawsuit based…there was probably a large award in your state. Similarly, I’ve always been annoyed that Indiana has a sign every few miles saying [about] “No sitting, standing or walking on shoulder.” Like the pastime in Indiana is hanging out on the freeway shoulders and the citizens have to be warned off.

Sometimes, they have to wait for materials to arrive or be fabricated before they can fix it. It’s a courtesy and a way to prevent lawsuits. Maybe people will be extra careful if they see the sign. Probably not, but at least they can say “I told you so”.

It’s cheaper to put up a sign than fix the rail.

Same idea as “Bumpy Road Ahead”

@elbanditoroso and “Bridge Out; Slow to 60”?

My sisters ex-husband took out a large section of a guardrail. The charged him for it and it was fantastically expensive.