Guardrail posts

At least around here, guardrails along the sides of highways always have metal posts along the bulk of the rail, but the first half-dozen or so posts are wooden on either end. (There's an exception when an end of the railing curves away enough, or when there's only a short gap in the railing.) I have been wondering why.

The exceptions make me think that the point of the wood is that that part of the railing is most likely to be blowed into headlong -- that's why it wouldn't apply in short gaps where you wouldn't easily be able to hit one end headlong without bouncing off the other segment, and in places where it curves out of the way.

But what purpose could the wood have there? Is it because it might absorb the blow more gently, or even shear off, and this would be better than being stopped dead (possibly literally)... whereas the kind of blow likely to hit the middle part of a guardrail is a lot more likely to be oblique or glancing.

I often wonder things like this, even though I can probably never find out about them, and get made fun of for wondering. (Which suggests a topic for tomorrow's blog post, actually.)