Air Foil A device placed on the back of a dump body or materials spreader that redirects and accelerates air passing over the truck. This is intended to keep the rear of the truck and materials spreader reasonably clear of snow build-up.  

            Angle of Attack The horizontal angle (less than 90^o) formed in plan view where the plow blade face deviates from a position that is parallel to the front grill of the plow truck 

Blade or Cutting Edge The replaceable portion of a plow that is closest to and is in contact with the pavement surface 

Ice blade A specialized plow blade that is designed to cut ice; these blades are usually placed on underbody plows that have down pressure capability 

Moldboard The portion of a plow between the top and the blade 

One-Way Plow or Funnel Plow A front mounted plow that will only cast snow in one direction (usually to the right) 

Rake Angle The vertical angle of the plow blade (cutting edge) relative to a perpendicular line from the pavement surface    

Reversible Plow A front mounted plow that is adjustable to cast snow: left, right, or straight ahead 

Snow Blower, Snow Thrower or Rotary Plow. A front mounted device, comprised of augers that move the snow to an impeller that throws the snow through a chute 

Underbody or Belly plow A plow that mounts between the front axel and the drive axel(s) of a truck or motor grader            

            “V” Plow A front mounted plow that simultaneously cast snow to the left and right 

            Variable Geometry Plow This is a front mounted plow with the ability to change the geometry of the moldboard 

Close Echelon Plowing.  Snow plows that are arrayed across the pavement in a way that prevents traffic from passing the operation. This prevents traffic from passing through windrows of plowed snow and is the safest and most cost effective procedure for high volume multi lane highways. 

            Snow Plowing The displacement of snow from paved surfaces with plows and wing plows. 

Snow Removal Physically relocating areas of accumulated snow.  This is usually a slow operation that may be accomplished with loaders and snow blowers     

           Tandem Plowing Snow  plows that operate in sequence, at a distance apart, that allows traffic to safely pass the operation. 

Windrow or Berm A linear (parallel to highway center line) accumulation of snow cast by a plow, other equipment or wind.             
 

Deicing. This is a reactive strategy for dealing with snow or ice that has already bonded to the pavement surface.  Deicing is most effectively accomplished by spreading a coarse graded (rock salt) solid or pre-wet solid ice control chemical on the surface of the bonded snow or ice.  The coarse particles will melt through the snow and ice, break the bond, and then produce a chemical solution that flows across the pavement surface between the packed snow/ice and road surface.  Any loose snow or ice should be removed by subsequent plowing.  Sufficient time is necessary to allow the salt to work before plowing commences. 

            Delayed Treatment. Delaying or not applying ice control materials is a tactic that may be used in support of the anti-icing strategy.  Road and weather conditions must be closely monitored to ensure success with this tactic.  This tactic should be considered when pavement temperature is likely to remain above freezing, or during “dry” snow and blowing snow events where pavement surface temperature is below 15^o F and there is no residual ice control chemical on the pavement.  Chemicals should not be applied in conjunction with plowing operations at these low temperatures or when plowing blowing and drifting snow at these low temperatures.  Usually snow will not bond to the pavement and can be effectively removed by plowing alone.  Traffic will whip the rest of the snow away.  In this situation chemicals, or the chemicals in abrasives, may make the snow stick to the pavement, causing icy spots that require continuing treatment. 

Level of Service (LOS) Desired or observed pavement conditions at various points in time, during and after winter weather events 

            Temporary Friction Improvement. This is an immediate and short- term improvement in surface friction that is achieved by spreading abrasives or abrasives/chemical mixtures on the snow/ice surface.  This method may be used in low level of service situations and where low pavement temperatures exist (below 15^o F). It is also useful on unpaved roads (with no chemical or the least amount of chemical possible). A major disadvantage of this method is that its effectiveness degrades quickly with traffic. Therefore, it is very important to monitor road conditions to determine if additional treatment is necessary.
 

            Anti-caking Agent A substance added to solid ice control chemicals to prevent caking or adhesion of the individual particles 

            Brine A solution of one or more salts 

Chemical Concentration. The percent (by weight ) of a chemical in a liquid or solid product 

Chemical Dilution Reducing chemical concentration by adding water or other substances 

Chemical Form The physical state of the chemical (solid or liquid) 

Endothermic Absorbs heat or becomes colder when going into solution 

            Eutectic Concentration The solution concentration that will produce the eutectic temperature. 

Eutectic Temperature The lowest temperature that an ice control chemical will melt ice or prevent ice from forming 

            Exothermic Gives off heat or becomes warmer when going into solution 

Gradation or Grain Size Distribution This is the proportion of solid material that is retained on specified screen sizes 

Hydrometer A device used to measure the specific gravity of liquids 

            Hygroscopic The property of having the ability to draw water from the air 

Ice Control Chemical. Any chemical applied to surfaces that will prevent ice from bonding or melt ice that has already formed 

Liquid Chemical The liquid form of a chemical or combinations of chemicals; usually a solution 

Mixed Abrasives A mixture of abrasives and ice control chemicals 

Phase Diagram A graph that shows the relationship between: solution concentration, solution freezing point and solution (pavement) temperature 

Solution A generally clear combination of water and other dissolvable substances
 

Automatic Anti-Icing /Deicing Systems Liquid chemical distribution systems that are placed at strategic highway and bridge locations that automatically apply liquid ice control chemical to the road when specified conditions are present

Dry Run Driving the snowplow route, beat or run in non- snow and ice conditions to become aware of features that may impact snow plowing and spreading materials 

Circle of Safety A visual technique used by equipment operators to gain awareness of evolving situations all around the equipment 

Passive Snow Control The control of blowing and drifting snow by using snow fence, plantings or highway design features 

Pre-Wetting Adding a liquid ice control chemical, or water to solid ice control chemicals before placement on the road 

Pre-Treating Placing an ice control chemical on the road before the beginning of a winter weather event 

          Snow, Beat, Route or Run Maps These are maps that show individual or groups of snow plow routes under various level of service and available equipment conditions; hazards and special treatment areas are usually identified  

           Treatment Cycle Time The time it takes for a truck to return to retreat a point on the beat/run, after treatment, including any reloading time; if reloading is required for every treatment run, it could be the time between leaving the loading point for successive treatment runs 

Calibration The procedure for determining that the desired rates of discharge are capable of being delivered by the materials spreader, and what settings of the control features will produce the desired rates 

Discharge Rate The amount of material being discharged, per mile, by the spreader or distributor (pounds pr mile or gallons per mile) 

Spread Pattern The transverse distribution of the ice control product across the highway (middle third, full width, high side wheel path, strips, etc.) 

Ground Speed Control the material being distributed by the spreader is automatically controlled to deliver the proper application rate, regardless of ground or truck speed 

Blow-Over A relatively minor accumulation of snow on the road that is primarily deposited by the wind. Road or lane closure would be unlikely if not removed. 

Damp There is a light coating of moisture on the pavement, with no visible water drops 

Dry No wetting is apparent on the pavement surface 

Frost A “white” non-homogenous coating of ice that usually forms on surfaces when the air temperature is above freezing 

Hard Pack or Snow Pack This is formed when saturated snow is compacted by traffic, usually accompanied by a drop in temperatures and the resulting ice is bonded to the pavement.   

Ice/Pavement Bond Compacted snow or ice that adheres to the pavement so strongly that only ice control chemicals or increasing pavement temperature will break the bond 

            Loose Snow Unconsolidated snow that can be blown by the traffic or wind into windrows, or off the road 

Slush An accumulation of snow that lies on an impervious base and is saturated with water in excess of the freely drained capacity.  It will not support any weight when stepped or driven on but will “squish” until the base support is reached. 

Snow Drift A significant accumulation of snow on a road that is primarily deposited by the wind. If not removed timely, road or lane closure could result. 

Thick Ice A much thicker coating of ice on the pavement than thin ice, formation may result from: freezing rain, freezing of ponded water, or freezing of melt water that is not able to drain properly. It may be clear or milky in appearance, and is generally smooth although it can have a rough surface 

Thin Ice A thin, clear coating of ice where the pavement surface can be seen; often called black ice 

            Blowing Snow Airborne snow that is primarily being transported by the wind; precipitation may or may not be occurring            

            Drizzle Light rain that is characterized by very small individual water droplets 

Freezing Rain.  Super cooled droplets of liquid precipitation falling on a surface whose temperature is below or slightly above freezing, resulting in a hard, slick, generally thick coating of ice commonly called a glaze or clear ice or non-super cooled raindrops falling on a surface whose temperature is well below freezing will also result in a glaze. 

Frost.  Also called hoarfrost.  Ice crystals in the form of scales, needles, feathers or fans deposited on the surfaces cooled by radiation or other process.  The deposits may be composed of drops of dew frozen after deposition and of ice formed directly from water vapor at a temperature below 32^o F (sublimation).  Frost most often occurs when air temperature is above32 degrees F and pavement temperature is 32^o F or below and is at or below Dew Point. 

Heavy Rain Rain, seemingly falls in sheets; individual drops are not identifiable; heavy spray can be observed several inches above the pavement surface 

Heavy Snow Snow that is falling at a rate of more than 1 inch per hour and visibility is less than ¼ mile 

Light Rain Small liquid droplets falling at a rate such that individual drops falling on a wet surface are easily detectable  

Light Snow. Snow falling at the rate of less than ½ inch per hour: visibility is greater than ½ mile 

Moderate Rain Liquid drops that are falling are not clearly identifiable on the pavement surface and spray form the falling drops is observable just above surface 

            Moderate Snow.  Snow falling a rate of ½ inch to 1 inch per hour per hour; visibility is greater than ¼ mile and less than ½ mile 

            Radiometer or Infra Red Thermometer A non-contact device that measures the surface temperature of pavements and other objects 

            R.W.I.S. (Road and Weather information System) A system that is comprised of atmospheric and weather sensors, pavement temperature and chemical sensors, a computer and software system for arraying data and data analysis and a communications system to move the data from point of measurement to the end user  

Sleet. or Ice Pellets  A frozen  mixture of rain and snow (pellets) that had been partially melted by falling through a layer of the atmosphere having a temperature above freezing, and subsequently refrozen by a colder layer or air near the surface of the earth 

White-out A short duration situation, within a snow storm, where visibility drops to only a few feet.

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