Midwest Research Institute Overview

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Midwest Research Institute
Solutions through science and technology
Guidelines for Snow and Ice Control Materials
and Methods Robert R. Blackburn Duane E.
Amsler Karin M. Bauer 10th AASHTO/TRB
Maintenance Management Conference Duluth,
Minnesota July 13-17, 2003
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Research on Snow and Ice Control Issues

• 1994SHRPs Development of Anti-Icing
  Technology
• 1996FHWAs Manual of Practice for an Effective
  Anti-icing Program
• 1999AASHTOs Guide for Snow and Ice Control
• Others

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Guidelines for Snow and Ice Control Materials and
MethodsNCHRP Project 6-13
Overall Objective
Develop guidelines for selecting roadway snow and
ice control strategies and tactics for specific
ranges of climate, site, and traffic conditions
found in the United States
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Definitions

• StrategyA careful plan or method directed at
  achieving a specific goal or goals
• TacticsThe systematic employment of available
  means or resources to accomplish a desired end
  condition of a strategy

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NCHRP6-13 Objective Coverage

• Guidelines apply to both state and local highway
  agencies
• Strategies and tactics refer to combinations of
  materials, equipment, and chemical and physical
  methods used in snow and ice control operations
  to achieve a defined LOS

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Level of Service (LOS)

• LOS for snow and ice control operations is a set
  of operational guidelines and procedures that
  establishes

• Timing
• Duration
• Type, and
• Frequency of treatments

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LOS Goals

• Distribute existing resources on a priority of
  treatment basis. (Resource-oriented policy)
• Assign pavement condition goals at certain times
  during a storm to various priority highway
  elements and then determine necessary personnel,
  material, and equipment to achieve goals.
  (Results-oriented policy)

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LOS Goals (cont.)
Two time frames of a winter weather event are
important for LOS goals

• Within-winter-weather-event LOS Amount of loose
  snow/ice/slush allowed to accumulate between
  plowing cycles Condition of the
  snow/ice/pavement interface (bonded or
  unbonded)
• After-end-of-event LOS Time to achieve
  particular pavement surface conditions

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Performance-Based LOS

• Pavement conditions at various points in time
  during an event (visual)
• Performance indices that relate amount of time
  pavement areas are snow/ice covered to total
  storm time (visual)
• Report cards (customer satisfaction surveys)
• Friction measurements at various points in time
  during an event

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Pavement Snow and Ice Conditions
(PSIC)Definitions
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Snow and Ice Control Operational Considerations
Relating to LOS

• Cycle time
• Type of material treatments
• Climate
• Weather

Precipitation type and amount Visibility
Wind speed and direction Air temperature
Relative humidity or dew point
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Snow and Ice Control Operational Considerations
Relating to LOS (cont.)

• Site conditions

Pavement temperature Amount of snow/ice
remaining after plowing and/or before chemical
treatment Presence or absence of ice/pavement
bond

• Traffic considerations

Traffic flow rate variations Traffic
speeds Blockages
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Snow and Ice Control Strategies

• Anti-icing
• Deicing
• Mechanical removal of snow and ice together with
  traction enhancement
• Mechanical removal alone
• Traction enhancement
• Combinations of strategies

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NCHRP 6-13 Field Data Collection

• Field-tested five strategy/tactic combinations
• Three-winter periods

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Strategy/Tactic Combinations Tested

• Anti-icing strategy with appropriate chemical
  forms on lower-volume primary highways and local
  roads
• Anti-icing strategy with appropriate chemical
  forms at selected highway locations
• Anti-icing or deicing strategy with appropriate
  chemical forms on lower-volume primary highways
  and local roads

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Strategy/Tactic Combinations Tested (cont.)

• Anti-icing strategy with liquid chemical
  applications on bridge decks to prevent
  preferential icing
• Mechanical snow and ice removal strategy with
  abrasives prewetted with liquid chemicals

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Participating Highway Agencies

• 24 highway agencies 13 state 1 provincial
  4 county 6 city or town
• 51 site locations

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Geographical Distribution of Participating
Highway Agencies
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Factors Influencing Choice of Snow and Ice
Control Material Treatments

• Dilution potential of chemical treatments Type
  and rate of precipitation Pavement condition
  Pavement surface condition Treatment cycle
  times Traffic volume and speeds
• Performance characteristics of materials Solid
  chemicals Liquid chemicals Prewetted solid
  chemicals Abrasives

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Strategy/Tactic Combination and LOS Expectations

• Within-event LOS LOS PSIC Low 5 and
  6 Medium 3 and 4 High 1 and 2
• After-event LOS Time (hrs) to achieve LOS
  a PSIC of 2 or 1 Low 8.0 Medium 3.1
  8.0 High 0 3.0

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Strategies and Tactics and LOS Expectations
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Operational Guidelines for Winter Maintenance
Personnel

• Solid chemicals Anti-icing Deicing Mixes
  of solid chemicals and abrasives
• Liquid chemicals Prewetting solid chemicals,
  abrasives, and mixes Pretreating for frost
  and black ice conditions Pretreating for
  general snow and ice events
• Abrasives

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Time to Freeze of a Chemical Brine

• Time to freeze increases linearly with chemical
  application rate for given pavement temperature
  and rate of precipitation
• Time to freeze decreases nonlinearly with
  increasing rate of precipitation for a given
  chemical application rate and pavement temperature

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Time to Freeze of a Chemical Brine (cont.)

• Time to freeze decreases nonlinearly with
  decreasing pavement temperature for a given
  chemical application rate and rate of
  precipitation

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Time to Freezing vs. WE/Snowfall Rate for a
Pavement Temperature Range of 28F to 31.5F
Using Liquid 23-percent Concentration NaCl
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Chemical Application Rate Determination

• Step-by-step procedure1. Pavement temperature
  and trend2. Dilution potential for precipitation
  and trend3. Adjustments to precipitation
  dilution potential for Wheel path area
  conditions Treatment cycle time Traffic
  volume/speeds 4. Judgment of existence of
  ice/pavement bond condition
• Use table look-up for application rate
  determination

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Precipitation Dilution Potential and Its
Adjustments
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Precipitation Dilution Potential and Its
Adjustments (cont.)
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Application Rates for Solid, Prewetted Solid,
and Liquid Sodium Chloride
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Application Rates for Solid, Prewetted Solid,
and Liquid Sodium Chloride (Cont.)
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NCHRP 6-13 Summary

• Pavement snow and ice condition index (PSIC)
  developed to evaluate effectiveness of snow and
  ice control treatments
• Index used to evaluate within-event and
  end-of-event LOS achieved by treatments
• Field-test results used to develop material
  application rate guidelines for variety of
  operating conditions