Minnesota Department of Transportation

511 Travel Info

Maintaining Minnesota's Highways

 

Frequently Asked Questions

How many snowplows does MnDOT have?

MnDOT has 839 snowplows, to cover 30,000+ lane miles operated by 1,500 full-time and 300 backup drivers.

Why do we salt the roads in the winter?

Salt is used to make the roads safer during the winter. Salt lowers the freezing point of snow and ice and keeps the snow “workable” so it is more easily removed. Salt can be used for anti-icing, deicing or melting. Anti-icing is a technique where a chloride is applied to the roadway prior to a storm to prevent the snow/ice from bonding to the pavement. Deicing and melting is when a chloride is applied after the storm has begun in order to break up ice and snow pack or to melt glare/black ice.

What are the limitations of salt?

The minimum practical application range for salt is a pavement temperature of 15-20° F and above. While salt will melt snow and ice down to a pavement temperature of -6° F, it can melt over five times as much ice at 30° F as at 20° F. Thus the effectiveness of salt is sensitive to small differences in pavement temperature. Snowplow operators attempt to apply only the amount required for temperature, time and use, too little and the roadway will refreeze, too much is a waste of money and resources.

When the pavement temperature drops below 15° F the effectiveness of salt is decreased significantly. At lower temperatures MnDOT will begin adding other chemicals to the salt such as calcium chloride or magnesium chloride that will lower the freezing point even further.

Wind conditions must also be considered when deciding to apply salt or other chemicals to the roadway. As temperatures drop and the snow becomes dryer, snow blowing across the pavement will stick wherever there is chemical present. This can create a hazardous condition that would not have existed if no deicing chemical had been applied.

The effectiveness of salt can also be affected by the pavement type. Salt works better on new asphalt (blacktop) than on concrete pavements.

In order to reduce salt bounce and scatter and to help it adhere to the pavement, salt brine or other liquid deicers are sprayed on the salt at the spinner on the back of the truck. This is called pre-wetting. This strategy helps to reduce the overall amount of chloride needed to return the roads to safe winter driving conditions. Pre-wetting also helps to jump-start the melting process, making the salt work more quickly.

How much salt and sand does MnDOT use in a typical winter?

The amounts vary considerably from year to year depending on the severity of the winter. The winter of 2012-13, a particularly severe winter, we used 304.6 thousand tons of salt and 44.3 thousand tons of sand, which compared to 2014-15, considered a more “average” winter we used 173.9 thousand tons of salt and 39.8 thousand tons of sand.

Why doesn’t the department use more sand?

MnDOT will use sand for traction when the temperatures are very cold and chemicals won’t work or during freezing rain events. But the benefits of sand applications are very limited. Sand doesn’t have any ice melting properties. Abrasives are also very easily displaced by traffic. There are also negative environmental impacts such as air pollution and siltation of waterways. Sand costs more than salt when you factor in the higher application rates, frequency of applications, costs of sweeping and disposal.

What is the importance of pavement temperatures? Why can’t you just use air temperature?

The ability of deicing agents to melt snow and ice depends on both the pavement temperature and the air temperature, along with the time of the winter season. During the fall, the pavement is often kept warmer than the surrounding air because of the warm soil. During the spring the reverse may be true. The pavement temperatures can be colder than the air because the soil is still frozen from the low winter temperatures. The sun also has a strong influence on pavement temperatures. Air and pavement temperatures can differ by as much as 20 degrees.

Is it legal to pass a snowplow?

There are no state laws that prohibit you from passing a snowplow. However, it can be very dangerous to pass a plow. Snowplows have wing plows that can be on the left or right side of the truck and can extend from 2-10 feet beyond the width of the truck. It can be difficult to see the wing if there is a snow cloud. The majority of crashes involving snowplows happen when a snowplow is rear-ended or hit when being passed.

Why is it I never seem to see a snowplow during a winter storm?

MnDOT is responsible for snow removal on 30,000 lane miles of roadway. Using the 839 trucks, the cycle time to complete a route can vary from 1-2 hours in urban areas or as long as 8 hours in rural areas. Time is also needed to load, reload and fuel trucks.

Why does MnDOT have its own weather reporting stations?

MnDOT currently has 97 Road Weather Information System (RWIS) stations throughout the state and will be installing 60 more in the next 4-5 years. RWIS stations are located on the right-of-way next to the highway with sensors imbedded in the pavement. These stations collect road surface and atmospheric information. The stations measure air and pavement temperatures, relative humidity, wind speed and direction, subsurface temperatures and depth of precipitation and salt concentration on the roadway. The information is used by superintendents, supervisors and plow drivers to aid in determining what material to use, when to use it and at what rate. RWIS weather data is also used by the National Weather Service and the National Oceanic and Atmospheric Administration and other forecasters on a year-round basis. The weather reporting stations can be accessed at: www.rwis.dot.state.mn.us

Why is there a difference in performance from storm to storm?

There are many factors that combine to make fighting storms challenging. Factors include: dew point/relative humidity, wind speed, gusts and direction, frost/black ice, precipitation type, duration and amounts, air temperature, road temperature, cloud cover, blowing snow, and surface pressure. At the end of each season each district uses these factors to calculate a single relative number or severity index. The winter of 2013-14 had a statewide severity index of 128 and the winter of 2014-15 was 87.

Why are you spraying water on the road on a perfectly clear day?

MnDOT is actually anti-icing, spraying a liquid salt solution on the roadway that will help keep snow and ice from bonding to the pavement. Anti-icing is similar to spraying oil in a frying pan to keep food from sticking to the bottom of the pan. The salt solution acts as a barrier so the snow and ice won’t form a strong bond to the pavement thus making it easier to plow off snow accumulation. In many locations MnDOT will anti-ice bridge decks the afternoon before a predicted frost. This application helps prevent frost from forming on bridge decks overnight.

Who is responsible for the winter road conditions report I see on the internet? Where can I get road condition information?

511 is a public service of the Minnesota Department of Transportation to help travelers access information about road conditions, traffic incidents, commercial vehicle restrictions, and weather information via the phone or the Web, 24 hours a day, seven days a week. During a Winter Weather Event, MnDOT’s 511 systems is the best way to get updated information for road conditions. Transportation department field crews provide information to update the system when conditions change to reflect the current conditions. Additional information comes from the Minnesota State Patrol, the National Weather Service, and the Road Weather Information System. 511 can be accessed at: http://511mn.org

Why does MnDOT close roads?

If weather conditions are so severe that it is unsafe for plows to operate, snowplows are pulled off the road until conditions improve. This only happens in the most severe conditions and is coordinated with the Minnesota State Patrol and is reported on MnDOT’s 511 systems.

What is the typical size of trucks in the department’s fleet?

MnDOT utilizes two basic categories of trucks in winter operations. A typical tandem-axle dump truck has a capacity of about 7 yards and a typical single-axle truck has a capacity of about 4.5 yards. Trucks are usually kept for 14 years and then sold at auction.

Who is responsible for plowing snow on a state highway in a city or town?

It could be MnDOT or it could be the city or county’s responsibility. In some communities, agreements between MnDOT and the city or county give the city full maintenance responsibility including the removal of snow and ice on the state highway through that location. These agreements can help provide for better continuity of service.

 

For more information, contact us here: http://www.dot.state.mn.us/information/submit.html.