ITD winter road-clearing arsenal features several weapons
NOTE: This is the first of a two-part series on tools and techniques ITD uses to ensure driver safety during winter highway conditions.
A handyman with only one tool in his toolbox is quite limited. If all he has is a hammer, he will have little luck pulling off a tire to re-pack wheel bearings. If he has a pair of pliers, but nothing else, he’ll find it difficult to drive a nail or shingle a roof. But arm that same individual with a variety of tools, and his efficiency is instantly transformed.
Like a well-prepared handyman, ITD has several products in its arsenal to treat highways to remove snow and ice for the safety of drivers. Some of the products are limited to specific regions of the state. Some are used quite extensively. Some are more effective at higher temperatures and give way to other techniques as the highway surface temperatures drop.
Idaho has a diverse landscape, from hills and mountainous terrain to stretches of flat, wind-blown high desert – often within the same region. Temperatures in those regions can vary as much as 20 to 30 degrees.That can make it challenging to find the best product for the area. Sometimes it a full toolbox.
ITD has four primary highway-treatment tools, in addition to plowing, which is undoubtedly the most visible snow-clearing process.
A liquid deicer, mag chloride is commonly used in the northern panhandle and southwestern regions, although it has been part of ITD’s statewide winter road-clearing toolbox for decades. It also is used in south-central Idaho, along with brine (a mixture of salt and water), salt-and-sand mix, and road salt, the rest of the ITD quartet. These other three will be explained later.
Mag chloride often is used as the first line of defense to keep the snow from bonding to the highway surface and creating ice. The amount placed on the road varies with the purpose of the application. In some locations it is not applied directly to the surface nearly as often as it is applied as a pre-wetting treatment for a salt-and-sand mix.
It is most effective when applied just before a storm. The distribution rate in southwest Idaho is usually 25-35 gallons per lane mile, depending on conditions. It has a low temperature range, but the021513 effectiveness of the product decreases as temperatures approach zero. It often is discontinued when temperatures drop. Some districts use it as a deicer in a variety of temperature ranges.
“In southwestern Idaho, we use magnesium chloride, a salt-and-sand mix and straight salt, each to varying degrees,” said District 3 Maintenance Operations Manager Tom Points. “We’ve done a lot of experimenting with different products over the years and have selected our products based on that research. Each area has unique weather patterns, and we have selected products to meet those needs. The products we are using give us the best performance for the lowest cost.”
Dave Dansereau, who operated a plow in the southwestern region the past 15 winters, added that “each of these products has specific conditions they work best in, and some of the variables we deal with are temperature, snow volume and traffic volume.”
“Before a storm event, the crews monitor weather forecasts and base their product selection on that. At times these products are used individually, but more often several products are used in a combination.
“For example, at the beginning of a storm we will pre-treat the roadways with mag, then switch to a straight salt or salt-and-sand mixture. The mountain areas usually do not use as much mag due to the colder temperatures and higher snow volumes - they get more of a salt-and-sand mixture.”
Road salt has been around as long as snow and ice. At lower temperatures, salt is used as a melting agent. ITD often applies salt right behind a snowplow to help melt the remaining snow and ice.
According to Steve Gertonson, ITD’s southeastern Idaho Maintenance Operations Manager, “road salt used during a storm on dry snow requires about an hour to change from the solid to liquid, turning the snow into slush which is then plowed off the roadway. When the snow is wet, or if the maintenance crews pre-wet the pavement, the melting occurs much more quickly. In the right conditions, it can be immediate.”
Rock salt is the most economical option of the four. By itself, it is most effective above 25 degrees F, and remains effective down below 10 degrees. “At the lower temps, it takes longer to get the job done, but it still works well,” said ITD Chemist Ron Wright.
The chloride effectiveness decreases as temperatures fall or precipitation dilutes the product. Field operators must adjust chloride applications based upon amount of precipitation on the highway and the temperature in order to ensure a workable roadway surface for each round of plowing.
(NEXT WEEK: A look at ITD's use of road salt and salt-sand blends.)