Snow and Ice Removal
About the measures
MnDOT measures the ratio of liquid to solid de-icing chemicals applied to reduce overall chlorides used on the roadway for snow and ice control in a winter season. Salt chlorides play a key role in keeping roads safe during winter months by lowering the freezing point of water. MnDOT is working to better manage pollutants by increasing the use of liquid chlorides compared to dry during snow and ice operations.
Based on traffic volumes, every state highway is assigned one of five time frames for clearing snow and ice after a winter event. These time frames, or targets, range from 0 to 3 hours for high traffic roads to 9 to 36 hours for less-traveled roads. The percent of bare lane targets measure tracks the frequency with which MnDOT achieves highway-specific targets over an entire winter season.
MnDOT uses a winter severity index to simplify the comparisons of winter severity from year-to-year. It also provides general context in which to review a winter season’s maintenance activities. At the end of each season, MnDOT districts use the following factors to calculate a single relative number: dew point/relative humidity, wind speed gusts and direction, frost/black ice, precipitation type and duration amounts, air temperature, road temperature, cloud cover, blowing snow, and surface pressure.
Recent trends
In the 2022-23 winter season, 54 gallons of liquid were used for every ton of salt, which continued the trend of increasing the use of liquids to de-ice roads. For snow and ice clearance, bare lane targets were reached 84% of the time. MnDOT has exceeded its 70% goal for all the of the previous 12 winter seasons. Additionally, MnDOT conducts a statewide public opinion survey asking people in Minnesota about their snow and ice removal perceptions. On average, respondents rated MnDOT’s performance 7.5 out of 10 (the highest possible score).
Also, for the 2022-23 winter season, the statewide winter severity index was 164, which was the highest value compared to the previous eight seasons. By MnDOT district, the winter severity index varied with District 1 receiving the highest value (177) and District 7 receiving the lowest value (75).
Where we want to go
MnDOT research has shown that at rates at least greater than 100 gallons per ton a 25% reduction in total chlorides can be realized. MnDOT’s target is to increase the frequency of using liquids to de-ice roads to 200 gallons per ton of solid by 2027. The transition from dry chlorides to liquid chlorides requires multiple investment areas, including equipment and staff education. Usage of the method varies across the state. Clearing snow and ice within the specified target reduces the impact of winter weather on people in Minnesota. Snow removal performance is affected by weather conditions, timing of the event, and the moisture content of the snow. In severe winters, districts may redirect summer maintenance funds to snowplowing activities. MnDOT uses technology and innovative strategies to increase efficiency.