Why brine and not just plain salt?
Simply put, mixing rock salt with water and applying it that way gets more bang for the buck. Tina Greenfield, with the Iowa Department of Transportation’s Office of Maintenance, said, “More often than not, we just brine to treat the roads, instead of using salt alone. There’s nothing magical about brine. It’s simply a mixture of salt and water. When the water evaporates, it leaves a film of salt that says on the road.”
Greenfield continued, “Mixing the brine ourselves allows us to take advantage of brine’s tendency to stick to things. This tendency actually reduces the amount of dry salt we need to use. Dry salt bounces a lot when it lands on the pavement; some studies estimate up to 30 percent soon ends up in the ditch when applying the completely dry material. When it makes more sense to use dry salt or sand instead of brine, we spray it with water as it is dispersed from the truck so it sticks to the road better. Since more material stays put, we can use less and reduce waste.”
Why spray on a clear, sunny day?
You may have noticed Iowa DOT snowplows out on the roads spreading brine on clear, sunny days. While it may seem counter-intuitive, the work we are doing is really important in keeping you safe and moving on the roads. Once the ground starts to cool down, the cold, clear nights provide the perfect conditions for frost to form on roadways. This is especially true on bridges and overpasses that don’t have warmer earth underneath them. That frost can be very slick and patchy, and few drivers are prepared for it.
In addition to making the roads safer by preventing slick spots, this process of anti-icing can save the Iowa DOT time and money because it allows roads to be treated during normal business hours when Iowa DOT garages are at full staff and not incur overtime to bring employees in overnight.
How concentrated is the brine we use?
For liquid brine, we use a salt and water combination 2.2 pounds of salt to 1 gallon of water for a 23.3 percent brine concentration. Dry salt will also form brine when it mixes with snow and slush on the road, although the concentration will vary.
How much does rock salt cost?
To help control costs, the Iowa DOT contracts for a year’s worth of salt at once. Craig Bargfrede, the Iowa DOT’s winter operations administrator, said this year’s statewide average salt price is around $70 per ton. He said, “Because of the way our contracts work, we are also able to offer cities and counties the opportunity to use our volume contract price to buy salt for themselves at lower prices than they could receive by buying themselves. Government entities must also go through a competitive bidding process when buying materials. Buying from us eliminates the need for them to go through the bidding process on their own, especially for smaller cities and counties with limited staff.”
We look at the five-year average salt usage to determine an amount to contract every year. Bargfrede said, “For the 2017-2018 winter season, we contracted for 150,850 tons of salt. We work with our field offices to come to an agreement on how much salt each of our 102 garages will need for the season. We work hard every spring to make sure the salt storage is full at the end of one winter season so we’re ready in case next season’s fall frost crops up earlier than expected.”
So now you know. The next time you see an Iowa DOT truck spraying salt on a sunny afternoon, you’ll know to be prepared for possible frost or ice on untreated roads overnight.