What is it? Where is it?

[HiloJulie]

Need more hints. Is this something I would encounter while biking, or is it a sign a driver would miss at car speeds?

kalianna had it real close with the guess of the roller coaster roads that are part of the Ainaloa/back roads to the Belt Rd.?

But as I mentioned earlier, depending on the direction you're going, you could be volcano bound, where if you are going the other direction, where you would have seen this sign, one could say you are Pahoa bound 

You could see it biking, and in a car driving reasonable speeds. The key is in the direction you are going.

One additional hint which no doubt will give it away, but the road it was on has a number and a name!