Weather Applications > Road-Weather Maintenance > Anti-ice Report

• Introduction
• System Description
  • Weather Information
  • Road Weather Information System
    • System Components
    • RWIS Programs
    • Road Information to Travelers
  • Snow and ice control strategies
    • De-icing
    • Anti-icing
    • Special Equipment
  • Benefits
• Projects and Applications 
• Information Dissemination
• Other Traveler Safety Technologies
• Related Websites
• References

INTRODUCTION

Roadway icing is a serious meteorological hazard causing serious injuries and even deaths. In cold climes, a large proportion of incidents are due to ice on the road. For example, in places like Eastern Washington,  roughly 25% (1996) of the total accidents were related to ice on the road.

Roadway icing occurs under conditions that are generally well understood and often predictable. Roadway ice formation occurs due to moisture at road surface during freezing temperatures. This can be due to the effects of frost, fog, frozen groundwater, snow or raindrops. Thus the knowledge of such conditions and accurate weather information is essential for planning ice removal plans and subsequent motorist information.

SYSTEM DESCRIPTION

Snow and ice can make driving hazardous. Hence highway agencies spend more than $2 billion annually in the United States on materials, crew time, and equipment to make travel more safe. Most of the effort goes toward clearing streets and highways but the Strategic Highway Research Program (SHRP) found that a more efficient process would be to treat the pavement before conditions make it ripe for snow to stick. This strategy, known as anti-icing, relies on information supplied by Road Weather Information Systems (RWIS).

Weather Information

Accurate weather information is the key to understanding an approaching storm and taking action before it hits. To know when it is time to begin anti-icing operations, maintenance managers must depend on an array of data from different sources, including RWIS (Road Weather Information Systems), and national and local weather forecasts. By combining forecast information with current pavement, subsurface and atmospheric data, meteorologists can predict probable changes in the pavement temperature and surface conditions. The results can lead to frost
probability forecasts and the sending of alerts to decision-makers. There are four basic sources for forecast information.

1. National Oceanic and Atmospheric Administration (NOAA) -National Weather Service

One source for regional and national weather information is the National Weather
Service (NWS). The NWS provides U.S. and worldwide forecasts, current weather condition reports from surface aviation observation stations, and public watches and warnings. This information is free and available on the Internet at the NOAA web site. Although available at no cost, NWS forecasts are usually not specific enough for maintenance managers to use for decision-making at the local level.

2. General weather consultants

A general weather consultant will typically provide mid- to long-range forecasts with more detail. Mid-range outlooks provide forecasts for the next 24 hours. Typical long-range or extended forecasts provide three to five-day outlooks. The longer the forecast covers, the fewer details it includes, and the less likely it is to be accurate. Three-day extended forecasts normally include information about probability of precipitation values, frost and fog probability forecasts, and storm watch and warning services. 

3. Customized forecast services

Several weather forecasting companies provide services that are tailored specifically to meet individual customer needs, such as for the aviation, construction and agricultural industries. These companies can also customize their forecasts for the transportation industry. Some of the most important elements of these specialized forecasts are the pavement forecast and bridge frost predictions. These elements are usually not available from other sources. Customized forecasts can be site-specific to an RWIS data collection location, or broadened to provide forecasts for an entire region or county.

4. Nowcasting consultants

Nowcasting means forecasting with local detail in the range of 0-6 hours in advance of a precipitation event. Nowcasting relies on information from various sources, including real-time data from RWIS sensors and observation systems, and local and regional climatological data. The information is used for making a judgment on the probable weather and pavement condition/temperature over the next few hours. Nowcasting can be an important tool when making the decision whether to initiate a treatment, when to start and call in personnel, and what treatment to apply.

Roadway Weather Information Services

For anti-icing strategies to be most effective, they must be paired with specialized road weather information systems (RWIS). A Road Weather Information System (RWIS) is a combination of technologies that uses historic and current climatological data to develop road and weather information (for example, nowcasts and forecasts) to aid in roadway-related decision making.  It consists of a network of monitoring stations located along primary roads and at potential trouble spots, such as bridges. By monitoring air and pavement temperatures to predict whether precipitation will freeze on the pavement, an RWIS allows highway agencies to make more informed decisions about where and when to deploy materials, crew, and equipment.

The three main elements of RWIS are

• environmental sensor system (ESS) technology to collect weather and road surface data; 
• models and other advanced processing systems to develop forecasts and tailor the information into an easily understood format; and 
• dissemination platforms on which to display the tailored information. 

System Components

These data are collected by sensors placed at the roadside or in the roadway itself. Remote processing units (RPUs) placed along the roadway contain some or all of the road and weather sensors. In some cases, the pavement sensors are located apart from the RPU, with several pavement sensors capable of being linked to one RPU. Since the RPUs have limited local intelligence for processing data, the data is transmitted to a central server, termed a central processing unit (CPU). This central server is typically located in a highway maintenance facility and provides communication, collection, archiving, and distribution of the data. The raw data are used directly or in coordination with a service provider to prepare nowcasts or forecasts. Forecasts can be used to predict site-specific weather and pavement conditions. Real-time weather information is important, although, the greatest benefits are accrued through the use of tailored forecasts such as those aimed specifically at supporting maintenance operations.

RWIS Programs

Foretell
FORETELL is a multi-state field operational test funded by the Federal Highway
Administration's Rural Intelligent Transportation Systems program. FORETELL is
combining advanced road data collection and weather prediction with other types of traveler information. The resulting RWIS will support seamless information sharing to benefit travelers, commercial vehicle operators, and transportation system managers. The FORETELL concepts are being tested in five states in the Mississippi Valley
region, plus western Ontario.
Website

rWeather
rWeather is the Washington State Department of Transportation's program for deploying a comprehensive, real-time and predictive system of collecting and disseminating statewide road and weather information. In the first phase of the program, WSDOT will concentrate on collecting data and predicting conditions.
Website

Aurora
Aurora is a long-term program of collaborative research, development, and deployment of advanced technologies for detailed road and weather monitoring and forecasting. The program, launched in 1996, brings together a number of U.S., Canadian, and European agencies, including the Minnesota, Iowa, New York, South Dakota, Virginia, and Wisconsin departments of transportation, the Federal Highway Administration, Ontario Ministry of Transportation, Ministere des Transports du Quebec, and Swedish National Road Administration.
Website

Road Information to Travelers

Besides being a tool for maintenance operations, RWIS can also be a source of
information for travelers. By transmitting the data to computer kiosks or the Internet, the public can directly access the information from their homes, or in rest areas, truck stops, hotel lobbies, airports or other public areas.

Snow and ice control strategies

The standard operational practice to control snow/ice was to treat roads with a 50/50 mixture of salt and sand once officials get notice that the road was becoming slippery. Often, trucks were not dispatched to the scene until a preset amount of snow or ice had already accumulated on the roads. This lead to potentially hazardous travel conditions for the public. Recently most agencies attempt to have materials and personnel on roadway in advance of winter precipitation and thereby reducing the time when roadways are slippery. The two main factors that helped in achieving this goal are proper training of operators and supervisors and having accurate weather information in the hands of decision makers. Accurate weather information also helps in warning the motorists about the conditions on the roadway and thus avert accidents. Most states get their roadway weather information from Roadway weather Information Systems.

There are two distinct snow and ice control strategies that use chemicals - deicing and anti-icing. They differ in their fundamental objective. 

Deicing
Deicing is an operation where a treatment of a deicing chemical is applied to the top of an accumulation of snow, ice or frost that is already bonded to the pavement surface. Deicing is familiar to most agencies since it has been the most widely used strategy in the past. It is commonly initiated after an inch or more of snow has accumulated and bonded to the road. By then, safe travel conditions have often deteriorated. Today, proven anti-icing strategies are being used by many transportation agencies as a proactive, preventative strategy.

Anti-icing
Anti-icing is the practice of applying deicing materials at the start or onset of a precipitation event in an attempt to prevent or weaken the bond of ice to the pavement by reducing the freeze point of water. As a result, roadways stay wet or slushy, making snow and ice removal easier. The key to a successful anti-icing strategy is knowing which chemical to use, in what amount, and when. The most commonly used chemicals for anti-icing treatments are calcium chloride, sodium chloride, magnesium chloride, and calcium magnesium acetate. 

Special Equipment
Specially equipped trucks with tanks, pumps, spreaders and sprayers are needed to apply anti-icing chemicals. A variety of models and designs have been developed by transportation agencies in conjunction with manufacturing and agricultural industries. Equipment is readily available on the market and selection should be based on user requirements. To reduce start-up costs, several transportation agencies have modified their existing equipment by adding special anti-icing equipment. 

Benefits 

Representatives of agencies who are currently using anti-icing and road weather
information systems state the following as the main advantages of anti-icing and RWIS :

• sustain or improve levels of winter maintenance service;
• prevent black ice, glazing or frost on bridge decks;
• reduce the time and effort required to return the pavement to a bare
  condition after a storm;
• improve environmental quality by reducing the use of chemicals and
  abrasives;
  
• improve efficiency of crew scheduling;
  
• reduce accident rates and improve overall safety; and
  
• reduce the wear on equipment by reducing the number of snowplow runs.

PROJECTS AND APPLICATIONS

Maintenance managers apply control, response and treatment techniques to mitigate threats posed by snow and ice. They employ mobile treatment techniques, such as plowing snow, spreading abrasives, and applying chemicals to improve roadway traction. Fixed treatment systems are operated in locations that are susceptible to slick pavement conditions due to local climatology, topography, and roadway geometry.

Anti-ice Spray in Illinois
The Illinois DOT has tested a magnesium chloride solution spray as an anti-icing technique on two bridges--one over a road in Tazwell County and one over a railway line in Woodford County. Vehicles have typically lost control and bounced off the guardrails along these bridges during winter freezes, and the anti-ice spray was intended to combat any black ice that may form on the road. The system fires off the spray nozzles in sequence so that each nozzle's burst lasts about one second. Information on pavement and air temperatures, surface conditions, wind speed and direction, and precipitation is sent to the DOT's weather forecasting service, which then coordinates the anti-icing sprays. The sprays can also be triggered by engineers remotely over the phone line.

Anti-ice Sprays in Wisconsin
The Wisonsin DOT has installed anti-ice spray systems on two river bridges on State Trunk Highway. These bridges often have hazardous early morning frost and black ice, which have caused cars to slide along the bridge and bump against the parapet railing. To address this problem, two spray nozzles were mounted on the guardrail posts on the bridge approach and four nozzles were mounted on the bridge parapet wall. A 511 ice warning system monitors the temperature on the pavement and that between 50mm and 75mm below the pavement. This information is fed into an algorithm, which then automatically triggers the anti-ice spray. The device can also be remotely triggered using a cell phone call. Although the state has not yet compared accident statistics from before and after the installation, maintenance supervisors have reported fewer accidents at the bridges. Although the installation of the anti-ice spray has been considered a success, there are no plans for further implementation.

SICOP
SICOP is the Snow and Ice Pooled Fund Cooperative Program.  It was developed by AASHTO (The American Association of State Highway and Transportation Officials). The goals of the program are to (1) sustain or improve levels of winter maintenance service with significant benefit/cost improvements, (2) provide an enhanced level of environmental protection, and (3) place technology in service on operational maintenance sections within two winter seasons. Another highlight of WMP is that it brought all levels of government together to cooperatively work on these projects. The concept of funding was also unique in that all funding will be via a pooled funding mechanism. Website

Anti-Icing/RWIS Training Program
A nationwide training program on anti-icing techniques and road weather information systems (RWIS) was jointly developed by the Federal Highway Administration (FHWA ), AASHTO Snow and Ice Cooperative Program (SICOP), and a pooled-fund research program known as Aurora.  The program develops interactive, computer-based training courses for three operating levels; equipment operators, supervisors, and middle managers.

A fully-automated anti-icing technology has been developed in Switzerland that allows for the accurate measurement rather than the calculation of the current freezing-point temperature. A weather station constantly monitors the micro-climatic environment; it is linked to a spray system (that is located in the pavement and sprays magnesium chloride), which is triggered when icing is about to appear. This system is intended to keep ice from forming in the first place.

Southeastern Michigan Snow and Ice Management (SEMSIM) Project
The Southeastern Michigan Snow and Ice Management (SEMSIM) Project is a partnership of the four largest road agencies in Southeast Michigan that is improving the efficiency of winter road maintenance through the use of cutting-edge satellite-based technologies, allowing quicker responses to changing weather conditions and improving interagency coordination. The tentative and brief scope of Phase I of the project (99-00) includes equipping winter maintenance vehicles in all four agencies with AVL equipment and sensors. The equipment will at least provide vehicle status on location, plow, salt, and pavement temperature. A customized software interface will allow quick viewing of current conditions as well as post storm review. Website

Winter Maintenance Virtual Clearing House
The winter maintenance virtual clearinghouse presents the most comprehensive picture of winter maintenance research and technology activities. This site is a work-in-progress hosted by the Federal Highway Administration and the former Anti-Icing/Roadway Weather Information Systems Team of the SHRP Lead States Program. Website

Bridge Deck Anti-Icing Project, Virginia
In Virginia, the numerous freeze-thaw weather cycles during winter seasons, acting together with the high levels of humidity can lead to frozen moisture and reduced friction on bridge decks while the adjacent roadway is unaffected. To combat this problem maintenance crews often treat bridge decks with chemicals and abrasives when no action is needed on the adjacent roadway.  VDOT is evaluating the effectiveness and practicality of automated bridge deck anti-icing spray system technology. The anti-icing system is composed of a reservoir, pump and a network of spray nozzles capable of applying a liquid anti-icing agent (magnesium chloride) on the travel lanes of a bridge deck. The control logic is programmed to activate the system in anticipation of frost or icing road conditions. More information

INFORMATION DISSEMINATION

Simple driver information such as traditional roadside warning signs have been in use for a long time to warn users about icy and slippery roads. Variable Message Signs (VMS) are also used to warn travelers of dangerous weather conditions. The public also used radio or telephone to access weather information.

Data Transmission Network (DTN) systems have been in use in many states for informing travelers about the current weather conditions. They provide near real-time radar and satellite weather information along with current and forecast information from around the US.  In 1996 Iowa DOT installed DTN systems in all rest areas along their Interstate system. The system was designed to provide 15 weather and travel related screens to the user, changing every ten seconds. The screens provided the travelers with real-time weather information and weather-alerts. 

The Automated Weather Observation Stations (AWOS) also provide very reliable near-time weather data. Computer synthesized voice broadcasts of the AWOS data can be received either by ground to air radio or by telephone. The AWOS information can also be accessed through the computer network. The computer network is a statewide network that uses dedicated telephone lines to connect all of the AWOS towers to a host computer via personal computers (PC) located at each AWOS site.  These PCs can be accessed by a direct modem connection.

Right now, the internet can be considered as one of the most valuable source of weather information. Most state DOTs, and Weather agencies disseminate weather information through the web. Click here for a list of such sites (provided by WS DOT's 'rWeather').
Some weather agencies also provide snow and ice alerts to their customers by e-mails and  cell phone calls. 

OTHER TRAVELER SAFETY TECHNOLOGIES

The roadside warning signs and Variable Message Signs (VMS) help warn travelers about inclement weather conditions. The newer technologies which would aid in traveler safety, and which are being studied in detail include the use of Advanced Driver Information and  the use of Intelligent Speed Adaptation.

Advanced Driver Information can be accomplished by introducing risk indicators in cars.
Intelligent Speed Adaptation (ISA) is usually a simple in-car device that reminds drivers when they are exceeding the speed limit on roads around schools and in other sensitive areas.  An in-vehicle unit receives a signal from a beacon mounted on the road-side speed limit sign. The  system checks the actual vehicle speed against the speed limit, and if necessary sounds a warning  to slow down.

Research and development on the concept of Intelligent Speed Adaptation and Weather related ISA, (WISA) is going on both regarding speed limits and dynamically changing limits due to the prevailing conditions (e.g. adverse road, or weather conditions). Ongoing projects on ISA (Sweden, 2001), include the active gas pedal, which provides a counter-force whenever the driver tries to depress it beyond a pre-set speed limit. A study conducted by the Technical Research Center of Finland (VTT) showed that if properly adopted the weather-reactive driver-support technology could reduce Finland's road traffic death toll. The study showed that the mortality reduction could vary from 1%, with a system providing winter road-condition information (such as, VMS) to 35% using Advanced driver Information and WISA.

RELATED WEB SITES

• FHWA's links
• AASHTO Lead States Web Site
• Alaska DOT ITS Project Page
• Idaho Transportation Department
• Iowa DOT
• Virginia DOT
• Pacific Northwest Snowfighters 
• FEMA Winter Storm Update Center
• Real Time Access to All NOAA NEXRAD Radars

REFERENCES 

1. A new approach (weather systems), ITS International, March/April 2000.

2. A WISA way to drive (Intelligent Speed Adaptation), ITS International, March/April 2000.

3. Iowa DOT Weather Information System to Support Winter Maintenance Operations, Mid-Continent Symposium and Spring Movite Conference Proceedings, May 15-16, 2000. 

4. Swiss roll towards better icing alerts, ITS International, Nov/Dec 2000 

5. Road and Weather Information Systems: A Concept and a Newsletter, Volume 1
Winter, 1999

6. Deborah Vocke, Learning to Beat Snow and Ice, Public Roads, January/February 2001

7. Conditions On The Information Superhighway: States Offer Varied Versions Of Web-Based Road/Weather Information WS DOT's rWeather, Volume 5 Spring, 2000/2001

8. The New generation of Snow and Ice Control, Anti-icing & RWIS,  Iowa DOT

Author: Indu Sreedevi, last update: 09/01/01