Planning for winter starts long before the snow falls


The weather is getting chilly, and you know what that means: winter is on the way.  Salt is the main chemical we use to treat roads in the winter. There are many ways to use salt including mixing it with water and spraying that salt brine on the road to help keep snow and ice from sticking. In the right weather conditions, solid rock salt can be used to help melt the slick stuff. However, getting the solid rock salt to stay where we put it can be a challenge. One that our snowfighters meet head-on, starting with testing the effectiveness of our salt spreaders.

Recently our winter research and steering committees, district maintenance managers, district mechanics, and researchers from the Institute for Technology at Iowa State University conducted testing on six different versions of salt spreaders from our garages around the state.

Tina Greenfield from our Maintenance Bureau led the testing. She said, “Our field forces are always coming up with new ideas and better ways of doing things. Three of the spreaders that we tested were developed, manufactured, and implemented by our own garage employees. The other three were commercially available options that are widely used in our 101 garages. It’s always great to see the innovation from our folks and how that stacks up to what’s available in the marketplace.”

Innovative ideas to deliver salt more effectively
With more and more of our trucks hauling trailers during winter operations, our crews have gotten creative with flexible salt chutes that can stand up to getting beat up by a trailer and still keep the material on the road.

The mudflap

Shop-built mudflap from Urbana

This innovation was originally developed in the Corning garage in 2010 after a discussion around the break table. It is now being used on several trucks in Southwest Iowa as an inexpensive way to get salt on the road and be indestructible while pulling a trailer.

Brandon Brim, highway maintenance supervisor in the Creston circle, says this salt distribution system works as well as it does because, “It is flexible and the sides are taller, which keeps the salt and brine concentrated in the wheel track better.”

The discharge hose

Shop-built discharge hoseThe Coralville shop has a history of innovation. This discharge hose was designed in 2017 by mechanics Jay Schwake and Tim Portwood. The design is pretty simple but very effective. The rubber hose holds the material together longer, puts the salt in the wheel track, and does not get plugged.

The premise of the design is to have a more flexible chute to distribute solid material when pulling a tow plow. The standard chute design and spinner would not work when towing a tow plow as these would get bent or damaged when turning corners.

Johnny Shanahan, the highway maintenance supervisor in Coralville, said, “There are currently five trucks with this design, but will be adding more this season to outfit all of our mainline trucks which will put us up to 13.”

The half-pipe

Shop-built PVC tile from CrestonWhile this innovation is designed to go on a truck pulling a trailer or tow plow, Mike Gallup’s crew in Urbana brought a half-pipe version to the testing. This innovation was developed a few years ago in Coralville as a cheaper and more efficient way to apply salt and brine, and not need a spinner, hydraulic motor, and hydraulic lines.

It is currently being used on four trucks, with four more being outfitted for next winter.  Gallup says the double wall tile does not let much if any salt fall off the sides like other chutes that have much lower sides. Also, more of a (bowl) design keeps all the brine/salt on the chute till it is on the roadway.


Putting the spreaders to the test

Since salt is only effective in melting snow and ice when it stays on the road the basic premise of the testing is to determine which of the spreaders keeps the most salt where it needs to be. This includes adding a bit of water to the rock salt, a tactic we call pre-wetting, to start the chemical reactions and help it stick to the road.

There were three variables used for this process.

  1. The spreader system
  2. The amount of water used to prewet the rock salt – five prewet rates were tested, starting with dry salt.
  3. The speed of the truck dropping the salt – three different speeds were used – 25 mph, 35 mph, and 40 mph.

Before testing, the spreader systems on each truck were calibrated at the De Soto garage by a team of our mechanics and operators. All trucks were loaded with salt and water from the same location. The testing was conducted at the Dallas County weigh scales, where an impermeable, smooth rubber mat was bolted to the parking area to simulate a 24-foot wide, two-lane road.  A grid of three-foot-by-three-foot squares was painted on the mat and each of the 10 grid squares was marked with a letter from A through J. 

Scatter grid

Each truck drove over the mat, with the spreader centered on box E. Using all the different configurations of the spreader system, prewet rate, and speed, a total of 57 test runs were made.

IMG_8437Following each run, the salt from each square was carefully collected and bagged. Once testing was complete, the 570 bags were taken to our materials testing lab where the salt was dehydrated and weighed. The data on the weight of salt in each bag was recorded and used to evaluate the effectiveness of each spreader system. Greenfield explained, “There is a lot of data to go over, but it’s pretty simple. In looking at all three variables in the testing, the more salt that stayed in the center portion of the grid, the more effective the treatment will be.”

In addition to the salt collection, the Iowa State University researchers recorded each run in slow motion to allow evaluation of the salt distribution frame-by-frame. Greenfield said, “It is important to have both of these data sources. The numbers from the salt collection can tell us ‘what’ is left on the road. The video can tell us ‘why’ that salt goes where it goes.”


The results are in

Greenfield said, “We were very pleased that the three systems developed by our own folks tested very well. In some cases, the new systems exceeded the performance of the older spreaders. The three ‘home-grown’ systems tested very similar to each other.”

Shop-built results
Average results of 25mph runs at 20 gal/LM and 10 gal/LM at both bar and spreader.


She continued, “As we have seen in previous testing in 2013, increased speed had a negative effect on the impact on all spreader systems. This round of testing also confirmed data from the 2013 testing that adding liquid tightened the spread pattern of the salt and reduced loss compared to dry salt.”

For DOTers who would like more information about these innovations or the testing, please reach out to Tina Greenfield in Maintenance or your district maintenance manager.  


Process-improvementEditor’s note: This post is part of a series related to our 5-year priority goal of “Supporting a Culture of Innovation” at the Iowa Department of Transportation. We are working to find innovative ways to improve processes, tools, & relationships to create positive experiences for our customers.

I found this very interesting and especially like the fact that employees who are "out there on the road" had the opportunity to work together to come up with multiple ways to improve the process of trying to keep the traveling public safe. Good job!

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