You know when you are driving along on the highway, you see either yellow or white reflectors on the road. These reflectors mark the lanes on the road, and they thump a little bit when you drive over them to let you know you are drifting out of your lane.
Then there’s the blue reflectors. Every once in awhile there will be a blue reflector located randomly along the highway. What the heck are those blue reflectors for? My WAG is they mark the route of a pipeline under the road.
Any ideas?
Here in Honolulu the blue reflectors indicate a fire hydrant is adjacent to the roadway on the side of the blue reflector.
Yeah, I vote for fire hydrant as well:
I will take note of that and see if they mark fire hydrants here (FL). Thanks.
I guess what I find strange is that they don’t seem to always be located in the same area of the road. Some are on the stripe, some are in the middle of the lane, some are just here or there.
Hydrants in Cal too.
CC, it’s a standard here in Florida too.
OK, I believe you. Thanks.
And hello neighbor 
St. Pete here.
Here in the UK, as well as the normal reflectors, we also have “Active” reflectors (or “cats eyes”). These actually have LEDs in them and are therefore not dependent on a passing car’s lights. They are red along the edges of the road, white marking the centre of the road and orange on intersections.
However, back to the OP, I have also seen an experimental version of these ‘cats eyes’ that are normally white but turn to blue as a warning that there is ice on the road. Pretty Cool…
Wow, that is very cool, very nice technology. I remember in Chicago when the season changed to winter, the roads would get icy but sometimes you couldn’t see it, they called it black ice. The only warning I ever saw for black ice was some other car’s headlights spinning around and then shining out from the ditch.
Yep… The reflector rule also applies in TX
In the mountains of Colorado, they are used to mark driveways, or where a culvert passes under the road.
This allows road crews to find the culverts in the winter.
On a late night drive down a divided highway, I too tried to suss out their meaning. I noticed that every time I saw one there was a cut through the grassy median dividing the lanes (you know, the kind that says ‘emergency or authorized vehicles only’) within half a mile.
I suspect the reflectors are so cops and rescue personnel needing to make a u-turn on the divided highway can rush along at high speed without having to go slow to look for the cut-through. Once they see the reflector, it’s a sign to slow down and prepare for the u-turn.
No hydrants here in Ohio, I see these alonge interstates where there are on hydrants.
For the straight skinny on this zombie thread, there is a Manual on Uniform Traffic Control Devices issued by the U.S. A. Federal Highway Administration that all states and local governments are required to use for all traffic control devices (although the states have been able to pass laws that disagree with it in some cases). Secton 3B.11 (on page 379) says: “Blue raised pavement markers are sometimes used in the roadway to help emergency personnel locate fire hydrants.” So that is a permitted usage. Link:
Before they were invented, cats kept bumping into things. 
I didn’t know about the hydrant thing in Florida either.
I didn’t catch the zombie thread status either. I’m off to a great evening here on the SDMB.
I was wondering this exact same thing… I kept seeing random blue reflectors in the middle of the right lane every so often and it was bugging the hell out of me wondering what it was for. I’ll have to look for a fire hydrant now!
Here in SC we have the same blue reflectors designating fire hydrants, as well as the yellow reflectors in the center of the highway. Several of them were inadvertantly scraped-off the highway in front of my house by snowplows during a rare measurable snowfall last February and have yet to be replaced.