Winter Maintenance - Plows and De-Icer

How does MDT prepare for the snow and ice season?

This winter, MDT will have approximately 900 trained maintenance personnel working to clear Montana's 25,000 lane miles of highway of ice, slush and snow. These employees will use a variety of winter maintenance vehicles including; snowplows, pre-wetters, spreaders, loaders and rotary snow blowers. If a snow storm covers the entire state, the miles required to plow the whole system equates to 2 times around the earth and will be accomplished within 24 hours!

During the year maintenance personnel prepare for the snow season by stockpiling necessary supplies. In the fall, the same trucks that have been used during the summer for stockpiling, patching and other maintenance operations are equipped with snowplows. Employees also receive training to operate new equipment and safety procedures.

What do the various road conditions mean?

Good Driving Conditions
Roads may be dry or wet. Visibility is not affected by weather conditions.

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Fair Driving Conditions
Roads are slushy or have scattered snow and/or ice. Snow covered roads are also considered fair driving conditions.

Slushy Scattered snow or ice Snowcovered
snowcovered road
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Severe Driving Conditions
Roads are covered with ice, black ice or a combination of snow and ice. Visibility is reduced due to blowing and drifting snow.

Ice/Black Ice
Reduced Visibility
Snow and Ice
Blowing and Drifting
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Road closed due to extremely hazardous conditions or accident. Blocked lanes (i.e. avalanche, rock slide, accident) may also force a road closure.

How does MDT decide which roads to clear first?
MDT considers these factors for clearing roads in the state highway system:
  • Traffic volumes
  • Accident reduction
  • Availability of manpower and equipment resources
  • Potential economic impact

MDT may apply winter maintenance chemicals to roads in many areas before a storm arrives or in the early stages of a storm to prevent snow and ice pack (anti-icing). MDT snowplow operators use "just-in-time anti-icing" guidelines to avoid unnecessary applications based on inaccurate forecasts. Once the anti-icing work is completed, MDT responds to winter storms as they occur and attempts to clear all roads as the snow continues to fall. However, in situations where a storm covers a large area, resources can be stretched beyond available limits. In these situations a system of priorities is followed to provide the best service.

Interstates and roads that have the highest volume of traffic are cleared first. Workers continue to clear roads with top priority placed on the most-traveled roads down to areas with lower volumes of traffic.

Some routes, because of concerns for public safety, high difficulty and cost of winter maintenance, may be closed for short durations until manpower and equipment resources are available for snow removal.

Materials Used for Winter Maintenance

Magnesium chloride is a salt compound extracted primarily from the Great Salt Lake, with added corrosion inhibitors, used to prevent or remove the buildup of ice and snow on the road. The effective working temperature for magnesium chloride is above 10 F on the road surface.

Sodium chloride is used in liquid and solid form and is primarily extracted from the evaporation of sea water. The effective working temperature for sodium chloride is above 15 F on the road surface.

Traction sand is crushed aggregate extracted from local gravel sources. Sand doesn't have any melting characteristics and is applied to provide temporary traction during a storm event. Unlike chemicals, sand doesn't lose its performance as the temperature drops. During extended below zero cold snaps, sand accompanied by a snowplow and educated operator may be the only tool left.

Chlorides work like anti-freeze by lowering the freezing temperature of water and preventing ice from forming a strong bond to the road. It helps keep roads from becoming slick, improves safety and reduces accidents.

Why do workers spray liquid onto the roadways before a big storm arrives?

If you live in Montana, you've probably asked yourself that question. It may seem dangerous to add liquid to a road that might freeze, but that liquid can be your best friend when winter driving conditions are at their worst. That liquid, can prevent snow from sticking to the road and prevent frost or black ice. It's one of the newest weapons against icy roads. Thanks to liquid chlorides, winter driving can be a safer experience. The following commonly-asked questions and answers will help you learn more about winter maintenance chemicals and the benefits they can offer motorists.

Is it safe?

Unlike sand, it won't crack your windshield or chip your car's paint. Tests have shown that the proper application of magnesium chloride or sodium chloride produces no negative effects on ground water, surface water or vegetation.

"Colorado Department of Transportation (CDOT) has completed a three-year study into the effects of magnesium chloride on the roadside environment and has found that the product does not significantly harm aquatic or plant life. Liquid de-icers or anti-icers are highly diluted in their usage and are even more diluted when they leave the roadway, mixing with melting water on the highway. The products are virtually undetectable within just a few feet of the roadway. The products do not add air pollutants to the environment and improves air quality by offsetting usage of sanding material. What's more, research into the use of liquid anti-icers and de-icers indicates that they have less negative impact on highway bridge decks, trees and vegetation, and water supply than any other method of winter road treatment utilized in the past. Liquid anti-icers and de-icers are the best products available for protecting many environmental resources."

Montana has not done a traffic safety benefit study, however, according to the Colorado Department of Transportation (CDOT), snow, ice and slush related accidents have also been drastically reduced statewide since the winter of 1995/1996 when CDOT began widely using liquid anti-icers and de-icers. Such reductions include a 76% reduction on I-70 west of Glenwood Springs in South Canyon, a 53% reduction on I-70 in the Vail area, a 89% reduction on SH 82 near Basalt, a 53% reduction on I-25 at the Mousetrap and a 64% reduction on I-70 at the Mousetrap.

How are liquid chlorides used?

Anti-icing: A light application of the liquid is made to a road before a storm to prevent a hard bond of ice, reduce snow buildup and speed snow and ice breakup after the storm.

De-icing: The liquid is applied to remove a thin layer of snow-pack or ice already on the road. It can be very effective for melting black ice and freezing rain.

Pre-wetting: Wetting traditional sanding material with liquid chlorides causes sand to stick to snow-pack better. Keeping sand on the road is nearly impossible in some circumstances, especially in very cold weather and in cases where there's traffic at highway speeds. Liquid chlorides can keep more of the sand from blowing to the shoulder of the road.

How does MDT determine when to use anti-icing and de-icing techniques?

A variety of factors are taken into account when deciding upon a course of action to treat winter roadways. Product application combinations are chosen after maintenance workers evaluate many factors including air temperature, pavement temperature, humidity levels, dew point temperatures, exposure to solar radiation, type and rate of precipitation, weather forecast, weather radar data, and satellite data. MDT monitors road conditions using infrared sensors, thermal mapping, and Road Weather Information Systems (RWIS).

Operational treatments are continuously evaluated by MDT before, during and after a winter weather storm. Road treatments and applications are modified through all phases of a storm based on careful analysis of intensity, duration and type of precipitation.

What can I do if I drive on roads where chlorides are used?

Wash your car on a regular basis. Chlorides (along with slush and dirt from the roads) can splash onto your car and build up after time, leaving a filmy residue on your car. Make car washing part of your regular maintenance routine, and you'll help keep residue from the winter roads off of your car.

As with any form of winter road treatment including sand or salt, liquid anti-icer and de-icer residue should be removed from vehicles with soap and water following winter weather storms. The products are no more damaging to the finish of vehicles than conventional sodium chloride-based products and will wash away with a good commercial car wash cleaning.

In making winter road conditions safer, the application of anti-icing and de-icing materials can create some road conditions that require particular attention on the part of motorists. Because liquid road treatments lower the freezing point of moisture on the road, travelers should be prepared for wet conditions. MDT recommends that motorists carry plenty of windshield wiper fluid in order to clear away any backsplash from the roadway, and are prepared to use their automobile's defrost system in the event that rising moisture may fog windows. Additionally, MDT reminds all drivers to obey posted speed limits with extra care on wet roads and to observe speed advisory plaques posted on curve warning signs. In fact, even the posted speed limit usually is too fast during adverse weather conditions. When liquid anti-icers and de-icers are applied, the road will be wet. Remember that when a highway is wet for any reason, traction is reduced and the chance of hydroplaning increases.

Why not use sand?

In many cases chlorides work better by preventing or removing snow-pack and the need for sand. It keeps snow from firmly sticking to the pavement and helps ensure a faster return to bare pavement. Sand can be crushed by traffic and produce airborne dust, which contributes to pollution (ten communities within MT don't meet Federal Clean Air Act standards and must use anti-icing chemicals instead of sand) - Because sand is easily blown off the road by traffic, it requires repeated applications. Washington, Oregon, Idaho, British Columbia and Montana joined together to develop standards for anti-icing products. Tests confirm the anti-icing chemicals in use on State highways produce no negative effects to water quality, vegetation, or wildlife.

Why does the sand product used by MDT include some larger debris more like gravel?

Sand and sand/salt mixtures are abrasives used to increase traction on slippery and icy roadways. Sand particles must be of significant size in order to provide effective amounts of traction. Additionally, finely ground sand would disperse into the air and contribute to pollution levels without providing sufficient coverage for traction. Current specification requires all crushed material to fit through a 5/16" opening.

For more information on MDT's winter maintenance program contact MDT's Maintenance Administrator: 406.444.6157.