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When a storm pounds the Wasatch Front the army of UDOT snowplows take to the roads to try and keep the commuting public mobile. It's a tough battle when the snow is coming down hard and temperatures drop. But they do have a major tool on their side, which we often see covering our cars windshield: salt.
Luckily Utah has a lot of salt mined locally, because many states have had problems getting it. And we spent part of this morning with Roger Frantz, a UDOT station supervisor in Parley's Canyon, to find out what it takes to wage the war against icy roads with salt.
Before the storm
When the word comes in that a snow storm is approaching the plow drivers hit the road. They take out the trucks with large liquid tanks and the spray liquid brine on the road as a barrier to prevent ice from forming. The brine lowers the temperature at which water freezes. The idea is the liquid keeps the snow from freezing to the road which makes it much easier to push snow and ice off the road with a snowplow.
What is brine?
The brine solution is about as simple as you can get. It is salt and water, nothing else. To make it they use a front-end loader to dump salt into a large metal mixing tank. Water bubbles up from the bottom of the tank into the salt and then the solution filters into a holding tank. They keep running the solution back through the salt until it's saturated and can't hold anymore salt.
The brine is then pumped into large storage tanks where it sits until it is pumped into a snowplow. They also have a pump system which helps them collect all the water used to make the brine at the Parley's canyon maintenance station.
The parking lot has a drainage system that leads to collecting ponds. All the snow that melts off the parking lot is stored until it's pumped to the mixer to make more brine.
Salt vs. Brine
Frantz says the biggest advantage to the brine is that it seeps down to the road surface and breaks bonds between the ice and the road. So it's the preferred method to get rid of black ice.
Salt alone takes about an hour to work completely. Once the salt is spread on top of the snow it starts turning the snow to water and works its way down. This helps give motorists better traction on snow and ice, but it's a long process. So, plow drivers want to get the salt as close to the road surface as possible.
During heavy snowfall Frantz says it's a waste to drop a lot of salt on the road because if the plows return to the same section in half an hour and plow again, they basically push all the salt off the road before it finished working.
UDOT estimates they use 224,000 tons of salt a year on the roads as well as 1.82 million gallons of salt brine. Frantz says one of their normal snowplow trucks can carry 10 yards of salt. If you estimate salt at around $20 a ton -- this price often varies -- that means every time the truck empties a load of salt on the road it costs around $200. Brine on the other hand stretches the use of the salt.
In every gallon of brine there is 2 pounds of salt in the mix. The snowplow trucks with liquid tanks hold 1,800 gallons of brine. So a truckload of brine costs around $36.
Temperature is a major factor in how quickly both the salt and brine works, which in turn affects how well the plows can get snow and ice off the road. The salt and brine work together to melt the ice, but they don't work well below minus 6 degrees Fahrenheit, which is a salt solution's freezing point.
So if it's minus 6 degrees outside it takes 1 pound of salt to melt three pounds of ice, which is not cost effective. If the temperature is 30 degrees, one pound of salt can melt 46 pounds of ice. So the plow drivers adjust the amount of salt they dump per mile based on the temperature.
Temperature is the key to getting the right amount of salt or brine on the road. The plows are equipped with sensors, which let the driver know the air temperature and the road temperature. An infrared sensor on the driver's side mirror bounces pulses off the road to get the road temperature. The driver then sets the salt level on the truck and the truck's system automatically adjusts the salt spreader according to the speed. So the driver can speed up and slow down and still spread the correct amount of salt.
The driver also has what they call the "blast" button. It's for when they go over bridges or other structures where the road surface typically is colder or needs an extra dose of salt or brine. Pushing the "blast" button literally blasts out extra salt. Some of the salt trucks also have small brine tanks near the back. These tanks spray the salt as it comes out of the truck; making the salt wet makes it start working faster.
The trucks, which carry only brine typically apply 30 gallons of brine per lane mile when it's extra cold and they can go around 44 miles before needing to refill.
Then a few plow drivers get to drive what they call a "half-and-half." It's a snowplow that hauls salt and is also equipped with a large brine tank. Frantz says it's the best of both worlds to spread salt and brine all together.