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Old 06-12-2019, 09:06 PM
elfkin477 is offline
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Sanded road?


About a week ago, I saw a road sign I've never seen before. This one, set just before an overpass type bridge, warned that there was a "sanded road." In June. Sure enough, though, there was sand scattered across the road. Why??

As you can imagine, asking google just brings up cites about slippery winter roads.

I thought perhaps there had been a mishap with a truck bringing pool sand somewhere, but it wouldn't explain the professionally made road sign. They don't put up signs warning you that roads have been sanded in the winter - of course they are - so it's not a leftover sign being repurposed.

They're now doing some bit of construction with metal plates on the end of the bridge, very close to where they sanded the road last week, so I assume this is connected to the purpose of the sand.
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Old 06-12-2019, 09:39 PM
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Around here they use fine gravel instead of sand, but either can be used. What they typically do is put down a thin layer of tar or asphalt and cover it with sand or gravel, whichever happens to be the less expensive option in your area.

It's a cheap way of resurfacing the road and making it last longer, so that they don't have to do a more expensive resurfacing quite as often.

I'm guessing in your case they are using it to smooth out the road surface after doing some work.
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Old 06-13-2019, 12:50 AM
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Something similar is/was the explanation for the otherwise mysterious sign you might see in rural areas of the UK: "Loose Chippings".
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Old 06-13-2019, 01:45 AM
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How dangerous is such a road? Driving down an ordinary paved road at 65 mph, what happens if you suddenly come to a section with a thin layer of fine gravel?
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Old 06-13-2019, 02:30 AM
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My whole length of county road is sanded tar, over a wash gravel road bed. It's not slippery. It is a mess when they redo it. That tar gets everywhere.

Last edited by Beckdawrek; 06-13-2019 at 02:31 AM.
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Old 06-13-2019, 03:18 AM
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https://en.m.wikipedia.org/wiki/Chipseal
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Old 06-13-2019, 06:10 AM
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How dangerous is such a road? Driving down an ordinary paved road at 65 mph, what happens if you suddenly come to a section with a thin layer of fine gravel?
There was one such road near me, it was one side (prong) of a fork in the road, it was fun taking it at speed where it would cause the car to slid sideways 'just a bit' making that turn and a vacant flat open field to end up on if the slid went a bit more then planned. Speed here would be about 35-40 mph. I found that out accidentally the first time I took that turn without that 'helper' sign to warn me.
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Old 06-13-2019, 06:18 AM
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How dangerous is such a road? Driving down an ordinary paved road at 65 mph, what happens if you suddenly come to a section with a thin layer of fine gravel?
I've never seen this on anything but back roads with low speed limits. Sounds fun and dangerous on the highway, noisy, scratching the hell out of paint, undercoatings, and brakes. Add this to the road hazards facing motorcyclists along with steel grate bridges and grooved pavement.
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Old 06-13-2019, 06:36 AM
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There was one such road near me, it was one side (prong) of a fork in the road, it was fun taking it at speed where it would cause the car to slid sideways 'just a bit' making that turn and a vacant flat open field to end up on if the slid went a bit more then planned. Speed here would be about 35-40 mph. I found that out accidentally the first time I took that turn without that 'helper' sign to warn me.
In my area, there's a side street that comes off the main road at an acute angle rather than 90 degrees. Because of this, if you're using that road (for a side street it's somewhat busy) you can just veer off to the left and barely slow down. Last summer it was covered in gravel before being resurfaced. However, the gravel was about the same color as the old asphalt so it was easy to miss. The first time I did it, my car actually fishtailed. I talked to a few other people that did the exact same thing.
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Old 06-13-2019, 07:26 AM
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Originally Posted by elfkin477 View Post
About a week ago, I saw a road sign I've never seen before. This one, set just before an overpass type bridge, warned that there was a "sanded road." In June. Sure enough, though, there was sand scattered across the road. Why??
How much sand, and what color? Were there freshly painted markings on the road?

One possibility is that they had recently painted lines on the road and coated them with glass-bead retroreflectors. The procedure I've seen is that they paint the line, and while the paint is still wet, a second spray head applies tiny spherical glass beads, which partially embed themselves in the paint:

Quote:
Originally Posted by Washington Post
Much more common is special retroreflective paint. Actually, itís not the paint thatís retroreflective but the thousands of little glass beads that are dropped into the still-wet paint ó or into hot and sticky thermoplastic ó just after itís applied. (How little? The beads range from 0.0024 to 0.034 inches in diameter.) The top 40 percent of each bead sticks up from the paint, casting light back at vehicles.
Those beads reflect incident light back approximately toward their source - so when your car headlights illuminate those painted lines on the road, the light gets sent back toward them, and - more importantly - to your eyes. This is why those lines look so bright at night.

In the situations I've seen, construction crews deposit a wretched excess of these beads, leaving a lot of them on the surrounding roadway. It looks like very fine white sand on the pavement. As the beads are smooth and round, they (when loose) are a major hazard for motorcyclists; if there are enough of them on the road, they act like a layer of tiny ball bearings under your tires. Perhaps this is what the warning signs were for?

Another possibility is that they were sandblasting metal parts of the bridge to remove rust before repainting, and they were warning motorists about waste sand that may have landed on the roadway.
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Old 06-13-2019, 07:49 AM
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Originally Posted by Machine Elf View Post
One possibility is that they had recently painted lines on the road and coated them with glass-bead retroreflectors. The procedure I've seen is that they paint the line, and while the paint is still wet, a second spray head applies tiny spherical glass beads, which partially embed themselves in the paint:



Those beads reflect incident light back approximately toward their source - so when your car headlights illuminate those painted lines on the road, the light gets sent back toward them, and - more importantly - to your eyes. This is why those lines look so bright at night.
Those beads are subjected to a lot of daily punishment just being driven over, and they get a little dull/dim over time. The solution is to spread a light coat of abrasive sand on the road and let traffic do the work or polishing those beads back into a reflective state.
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Old 06-13-2019, 08:16 AM
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How dangerous is such a road? Driving down an ordinary paved road at 65 mph, what happens if you suddenly come to a section with a thin layer of fine gravel?
(My question was of specific interest to me due to a nightmarish event I may have recounted before on these boards. Would hitting gravel at speed possibly send a car soaring completely off a 2-lane road?)
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Old 06-13-2019, 08:21 AM
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Originally Posted by PatrickLondon View Post
Something similar is/was the explanation for the otherwise mysterious sign you might see in rural areas of the UK: "Loose Chippings".
That was the name of the village you were passing through.

When I was living in Carson City there were two ways into the neighborhood where we lived, one way paved, the other about three miles of dirt road. When they resurfaced US50 at the other end of the dirt road, they used the milled detritus to improve the surface of the dirt road.
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Old 06-13-2019, 08:24 AM
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One of the jobs the work crews did in "Cool Hand Luke" was sanding over a freshly tarred country road. Must have been awful work in the southern heat.
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Old 06-13-2019, 09:27 AM
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Originally Posted by septimus View Post
How dangerous is such a road? Driving down an ordinary paved road at 65 mph, what happens if you suddenly come to a section with a thin layer of fine gravel?
One of the routes I take home did this. I believe they put down oil and then sanded over it but, in any event, there was a "Loose Sand" warning on a road that's listed as a 55 which means everyone does 65. I slowed down to 45 for the stretch and it wasn't exactly fun but not treacherous either. Like driving on a lightly snowed street. But I also knew it was coming versus random sand patches on the road unannounced.
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Old 06-13-2019, 10:11 AM
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(My question was of specific interest to me due to a nightmarish event I may have recounted before on these boards. Would hitting gravel at speed possibly send a car soaring completely off a 2-lane road?)
Where I grew up they would put tar and gravel on some of our roads every few years to resurface them. The clatter of gravel bouncing off the underside of your car was enough to slow everyone down. I don't think I ever saw any accidents as a result, it was just like driving on a rough dirt road.
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Old 06-13-2019, 10:19 AM
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One of the routes I take home did this. I believe they put down oil and then sanded over it but, in any event, there was a "Loose Sand" warning on a road that's listed as a 55 which means everyone does 65. I slowed down to 45 for the stretch and it wasn't exactly fun but not treacherous either. Like driving on a lightly snowed street. But I also knew it was coming versus random sand patches on the road unannounced.
In the incident I'm thinking of, the gravel layer was rather thickish than thinnish. It was an almost-empty road at night-time; there was a yellow diamond sign (I think it just implied 'construction ahead' rather than anything more specific), but some drivers might miss or ignore the sign. The speed was somewhere between 65 and 70 mph (Though in a country that uses kph).

May I ask the Board's excellent physicists? What are typical outcomes when the driver suddenly hits this gravel at 67 mph? It was a cheapish passenger car or pick-up if it matters.

ETA: Perhaps the gravel was thicker than just 'rather thick'.

Last edited by septimus; 06-13-2019 at 10:21 AM.
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Old 06-13-2019, 11:15 AM
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I'm not a physicist of any sort, but I would expect that if you don't supply any inputs to the vehicle (accelerate, decelerate, steer) you would pass over the gravel/sand with no problem (aside from potential paint chipping as mentioned). I grew up driving on a lot of gravel roads, and unless the gravel had just been put down, we crazy teenagers (and some of the grizzled farmers) would easily hit highway speeds (50-70 mph). And the slowing for new gravel was more about throwing rocks around then handling (although there was a handling component).
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Old 06-13-2019, 11:32 AM
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They definitely haven't paved.

Do you think sand blasting could have exposed the metal plates to the bridge, though? As I said, it's an overpass bridge so I assume that the plates were under pavement until recently.
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