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Why doesn’t the DOT salt the roads when freezing rain is forecast?

UNC71-00

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We are supposed to have a big ice storm starting around 2am and I noticed that the roads weren’t being treated at all. Yet if the forecast is for only an inch of snow, the DOT puts down brine before it starts.

How come that be?
 

Cooper

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We are supposed to have a big ice storm starting around 2am and I noticed that the roads weren’t being treated at all. Yet if the forecast is for only an inch of snow, the DOT puts down brine before it starts.

How come that be?
What is the temperature forecast where you are? if the temp is too low salt is not effective. The colder it gets the less effective it is and at 10° or below it doesn’t work.

Depending on your location supply may be tight as well.
 

UNC71-00

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What is the temperature forecast where you are? if the temp is too low salt is not effective. The colder it gets the less effective it is and at 10° or below it doesn’t work.

Depending on your location supply may be tight as well.

It will get to about 30 tonight. I’m in NC and unless the DOT forgot to place their annual order, we should have plenty.

The only thing I can come up with is that freezing rain hits the ground as water and then freezes. Maybe the rain washes the brine off and then it just freezes as if it were never put down?

I dunno
 

Jakethedog

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It will get to about 30 tonight. I’m in NC and unless the DOT forgot to place their annual order, we should have plenty.

The only thing I can come up with is that freezing rain hits the ground as water and then freezes. Maybe the rain washes the brine off and then it just freezes as if it were never put down?

I dunno

That was my thinking but I'm no brine expert
 

AgEngDawg

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I think it has to do with the dissolving of the salt or further diluting the brine is an exothermic process. It releases heat/energy.

Hence, if you do it before the cold temperature you don't get the benefit.
 

STMF2X

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I think it has to do with the dissolving of the salt or further diluting the brine is an exothermic process. It releases heat/energy.

Hence, if you do it before the cold temperature you don't get the benefit.

SarcasticSnoopyCanary-max-1mb.gif
 

UNC71-00

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I think it has to do with the dissolving of the salt or further diluting the brine is an exothermic process. It releases heat/energy.

Hence, if you do it before the cold temperature you don't get the benefit.

I don't think this is it because they brine the roads before a snow comes- it's a liquid brine though. The rock salt goes down after the snow.,
 

AgEngDawg

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I don't think this is it because they brine the roads before a snow comes- it's a liquid brine though. The rock salt goes down after the snow.,
I googled it:

How Road Salt Works​

Road salt works by lowering the freezing point of water via a process termed freezing point depression. In a nutshell, the salt breaks into its component ions in a small amount of liquid water. The added particles make it more difficult for the water to freeze into ice, lowering the freezing point of the water. So, for road salt to work, there needs to be a tiny bit of liquid water. This is part of the reason why road salt is not effective in extremely cold weather when water would freeze too easily. Usually, an extra source of water is not necessary because there is enough liquid water present, either coating the hygroscopic salt pieces or produced by friction from traffic.


When cold weather is forecast, it is common to pre-treat roads with brine, which is a solution of salt and water. This helps prevent ice from forming and reduces the amount of road salt needed to de-ice the surface later. Once ice starts to form, road salt is applied in gravel or pea-sized chunks. Road salt may be mixed with dry or damp sand to aid the process, too.
 

UNC71-00

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I googled it:

How Road Salt Works​

Road salt works by lowering the freezing point of water via a process termed freezing point depression. In a nutshell, the salt breaks into its component ions in a small amount of liquid water. The added particles make it more difficult for the water to freeze into ice, lowering the freezing point of the water. So, for road salt to work, there needs to be a tiny bit of liquid water. This is part of the reason why road salt is not effective in extremely cold weather when water would freeze too easily. Usually, an extra source of water is not necessary because there is enough liquid water present, either coating the hygroscopic salt pieces or produced by friction from traffic.


When cold weather is forecast, it is common to pre-treat roads with brine, which is a solution of salt and water. This helps prevent ice from forming and reduces the amount of road salt needed to de-ice the surface later. Once ice starts to form, road salt is applied in gravel or pea-sized chunks. Road salt may be mixed with dry or damp sand to aid the process, too.

Which brings us back to my original question- why do they brine the roads before snow but not before freezing rain?
 

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