References on salt for winter roadway safety & mobility
- General references
- How road salt works
- Roadway operations
- Liability and risk management
- Roadway safety
- Snowfighting management
- Transparency and accountability in snowfighting
- Road weather technology
- Snowfighting history
These references supplement our discussion on highway deicing and anti-icing for safety and mobility and the public policy issues arising from the use of road salt (we also have other references on the policy issues regarding road salt use ). They also supplement the significant publications and A-V materials produced by the Salt Institute . In addition, the Institute's Education Center contains curricula and training materials for snowfighter training .
The Federal Highway Administration calculates that 70% of U.S. highways are in snowy regions . Thus, winter roadway operations ("winter maintenance") is a core responsibility for most state and local transportation agencies, toll road authorities and snowfighting contractors. Their use of salt is integrated into their overall snowfighting strategies and critical to achieving their goals of safe and reliabilty-available roads and parking lots.
Those who live in sunny climes or flee winter's snow and ice events often need a reminder of exactly why it is important to perform winter maintence. These YouTube video clips are your reminder:
- "Bumper cars on ice in Portland " (all-time favorite)
- "Black ice can be a real hazard "
- Minnesota Highway Patrol video
- "Icy hill car crash "
- "Multi-car crash snow slide "
- "Snow car crash "
- "Icy car crash "
Moving now to prevention, consider resources and references in these groupings
- How road salt works
- Roadway operations
- Liability and risk management
- Roadway safety
- Snowfighting management
- Road weather technology
- Snowfighting history
- Links to organizations with more information
HowStuffWorks.com asks "Why do they use salt to melt ice on the road in the winter?"
A number of researchers have conducted experiments on particle penetration and ice disbondment characteristics of various deicers. Variables include deicer unit weight, particle size, atmospheric conditions, substrate temperature, etc.
Reaction times range from a few minutes to several tens of minutes. Data from experiments indicate the initial ice-melting reaction begins almost immediately upon application, depending on the deicer’s eutectic and the temperature of the ice, pavement, and air. Undercutting at the ice-pavement interface takes longer because the particles must penetrate the snow-ice mass to reach the pavement interface. Lower temperatures flatten the curve. For example, Nixon, et al. compared deicer penetration and ice undercutting capabilities of NaCl wetted with CaCl2 and untreated NaCl. The authors showed that NaCl penetrated ice immediately and undercut the ice in 5-6 minutes at a temperature of 10 ºF (–12.2 ºC). Their work indicates that NaCl wetted with CaCl2 accelerates penetration reaction time for the first few minutes after contact. The curves become parallel within approximately ten minutes.
McElroy, et al. (1988) compared ice undercutting rates and deicer application rates for seven deicers and mixtures of deicers. Variables include temperature, time, and application rate. The authors presented laboratory data showing that CaCl2 begins undercutting a 1/8 in layer of ice in 7-8 min at 15 ºF. Similarly, NaCl begins undercutting in 17-18 min; and KCl and urea begin undercutting in >60 min. Dickinson (1959) compared amounts of ice melted by mixtures of calcium and sodium chloride at different temperatures and time intervals. He showed that CaCl2 melted 2.5 lb ice/lb of deicer and NaCl melted 1.6 lb ice/lb in 15 min at 20 ºF. Dickinson’s Table 2 includes data for temperatures from 0 ºF to 26 ºF and time intervals of 15 min-6 hr. These data indicate that ice melting begins almost immediately. Sinke et al. (1976) Compared ice undercutting rates for NaCl and CaCl2 at various temperatures. They showed reaction times for NaCl of approximately 5-8 min at 15-25 ºF and reaction times for CaCl2 of 2-5 min under the same conditions.
Kaufmann (1960), referring to B. C. Tiney (1934), showed comparative melting capacities of calcium and sodium chlorides at various t temperatures. NaCl melted quantities of ice varying from 3.2 lb at -6.5 ºF (eutectic) to 46.3 lb at 30 ºF. 77%-80% CaCl2 melted 3.7 lb of ice at -6.5 ºF and 31.1 lb of ice at 30 ºF. Kaufmann also reported on penetration time in minutes of grains of NaCl in ice, based on grain size and temperature. A 1/8” salt grain penetrated >1” in 20 min at 25 ºF and 1” in approximately 50 min at 8 ºF. Larger particles penetrated to a greater depth. A ¼” particle penetrated 2” in 50 minutes at 25 ºF and 2” in 120 min at 8 ºF.
Dickinson, William E. 1959. Ice-Melting Properties and Storage Characteristics of Chemical Mixtures for Winter Maintenance. Highway Research Board Bulletin 220. 38th Annual Meeting January 5-9.
Kaufmann, Dale W. 1960. Sodium Chloride, The Production and Properties of Salt and Brine. Reinhold Publishing Corporation. Chapter 23, pp 562-565
Kersten, M.S., L.P. Peterson, and A.J. Toddie, Jr. 1959. A Laboratory Study of Ice Removal by Various Chloride Salt Mixtures. Highway Research Board Bulletin 220. 38th Annual Meeting January 5-9.
McElroy, A.D., Robert R. Blackburn, and Henry Kirchner. 1990. Comparative Study of Chemical Deicers – Undercutting and Disbondment. Transportation Research Board Annual Meeting. January.
McElroy, A.D., Robert R. Blackburn, Jules Hagymassy, and Henry Kirchner. 1988. Comparative Study of Chemical Deicers. Transportation Research Record 1157.
Nixon, J.G., D.R. Larrimore, and E.H. Mossner. 1979. A Laboratory Comparison of Prewet and Untreated Rock Salt as Ice Removal Agents. Dow Chemical Company.
Sinke, G.C. and E.H. Mossner. 1976. Laboratory Comparison of Calcium Chloride and Rock Salt as Ice Removal Agents. Transportation Research Record 598. Maintenance Management, The Federal Role…
Tiney, B.C. 1934. Highway Research Board, Proc. 13:333
Trost, Susan E., Frank J. Heng, and E.L. Cussler. 1987. Chemistry of Deicing Roads: Breaking the Bond Between Ice and Road. Jour. Transp. Engrg. Vol. 113, No. 1. January 1.
Highways are the arteries of our commerce and their availabilty is a cultural expectation. The U.S. highway system is described in the annual Federal Highway Administration (FHWA) Highway Statistics report. Transport Canada produces an annual Transportation in Canada report. The contributions of the U.S. Interstate Highway System have been particularly important in preserving international economic competitiveness. FHWA also produces an annual Condition and Performance report on the highways that goes well beyond pavement condition to consider operating performance .
The Federal Highway Administration is the driving force advancing a focus on improving highway operations (i.e. combatting congestion). It promotes the concept of "travel time reliability " as a key measure. FHWA created the National Transportation Operations Coaltion (NTOC) to further research and policy development. The Salt Institute is an active participant. NTOC Talks sponsors online forums and webinars .
The Transportation Research Board (TRB) of the National Academy of Sciences is also a strong promoter of improving operating performance of the highway network. Its Performance Measurement Committee is trying to develop a metric for assessing system operating performance. The Salt Institute serves as liaison between this committee and TRB's Winter Maintenance Committee . TRB strongly supports management policies linking customer needs and preferences to operating decisions like snowfighting.
The Transportation Association of Canada has produced an invaluable review of the state of practice in use of roadway surface friction measurement as a metric for assessing the adequacy of winter operations activities.
Private contractors perform winter maintenance service for many roadway agencies, particularly in Canada and Scandinavia. VMS, Inc. has prepared a white paper on Best Practices in Outsourcing Winter Maintenance Services (pdf 699.79 kB) .
Other key promoters of improving highway operations, besides the Salt Institute, include:
Roadway Safety Foundation (RSF has urged "Put the Brakes on Fatalities" arguing "We can significantly reduce crash-related fatalities by employing ... safety features, such as dedicated turning lanes, installing rumble strips and removing ice and snow in a timely manner." -- emphasis added)
AAA Foundation for Traffic Safety (see its report on Crashes vs. Congestion -- What's the Cost to Society? )
Key data on roadway operations outcomes are available from the DOT Bureau of Transportation Statistics .
Washington state DOT has compiled a list of state performance management/operations-oriented initiatives .
The January 2002 issue of Research Technology Transporter
has a good, brief discussion about operations.
Liability and risk management
There are innumerable court judgments awarding injured parties compensation when agencies fail to maintain roadways in a safe condition.
One-third of all traffic crashes are highway related -- half of them, 17% of the total, weather-related. More than 7,000 deaths and 800,000 injuries on U.S. roads every year are weather-related. Many of these occur on snow- and ice-covered roads where timely snowfighting can render them safe.
The most important reference is the Salt Institute-sponsored study by Marquette University, "The Marquette Report ," which examines the safety impacts of deicing.
This widely publicized study by Marquette University was the first of its kind in North America to document, with statistical validity, the direct benefits of deicing operations. It was patterned after a German study of the Technical University at Darmstadt during the late 1980s. The Marquette study was conducted during the winter of 1990-1991 in four states: New York, Illinois, Minnesota and Wisconsin. It covered a network of 520 miles of randomly selected twolane undivided highways and 50 miles of multi-lane divided freeways in the four states. The sections included were primarily rural or sub-urban.
Data collection included estimated hourly traffic volumes, accidents, and operating parameters including the time and amount of de- icer used for equal 12 hour periods before and after “zero” hour (the hour of the actual spreading of deicer). The direct costs of the operation were also collected and calculated. Estimates of traffic volume reduction due to snow, travel time reduction and the costs associated with the above items were made using standard methodology. Data on winter events were obtained from event logs of the organizations and meteorological data available about the storms. The data collection included over 125 test sections in the four states and a total of 226 events, with almost 4600 sub-events (a single event on a single test section).
For two-lane highway sections, the rate for all accidents was about eight times higher in the four hours before than it was in the four hours after “zero” hour (hours with the most significant difference). The rate for injury accidents was nine times higher before than after and for property damage only 7 times higher. There was an 88 percent reduction in accident costs in the four hour after period. The ratio of direct benefits to direct costs was about 6.5 to 1. The average direct costs were paid for after the first 71 vehicles used the highway, or paid for in about the first 25 minutes aft er the “zero” hour.
For freeways, the rate for all accidents was about 4.5 times higher in the two hours before (hours with the most significant difference) than after “zero” hour. The rate for injury accidents was seven times higher before than after, and the rate for property damage accidents was two times higher before than after. There was an 88 percent reduction in accident costs in the two hour after period. The ratio of direct benefits to direct costs was about 3.5 to 1. The average direct costs were paid for after the first 280 vehicles used the highway, or paid for in about the first 35 minutes after “zero” hour.
Another examination of the safety impacts of deicing was completed by Keith Knapp at Iowa State University. His paper, "Mobility and Safety Impacts of Winter Storm Events in a Freeway Environment " found performing winter maintenence reduced crashes by an astounding 1,300%!
The Canada Safety Council knows winter maintenance is the key to safe winter driving .
We depend on our mobility, both personally and in our business lives. And, it's not a pretty picture. Not much has changed in recent years from the effective summary of the situation produced in 2001 by the Democratic Leadership Council in its Blueprint Stuck! booklet. In it, Alan E. Pisarsky lays out the facts in "Life in the not-so-fast-lane ." Pisarsky notes that today's rush-hour commute in large cities has become twice as bad as it was in 1982. And that's before weather adds "non-recurrent" delays to normal "rush hour." The same booklet has an article by Ken Orski on how intelligent transportation systems will help prevent gridlock and the editors have a useful perspective .
FHWA developed several reports on trends in Traffic Congestion and Reliability that are models of the right questions to ask.
In a 1976 report, Benefits and Costs in the Use of Salt to Deice Highways, by The Institute for Safety Analysis (TISA), Washington, DC, using 1976 prices and rates, the use of deicing salt
- reduces wages lost due to lateness to work by $7.6 billion
- saves $3 billion in wage loss because of absenteeism
- reduces production losses by $7 billion
- reduces losses in goods shipment by $600 million
- saves 370 million to 1.2 billion gallons of fuel
- has an 18:1 benefit:cost ratio
Even though the federal government does virtually no snowfighting itself, FHWA recognizes the key role of snowfighting to achieving its performance goals to improve safety and reduce congestion. Improving response to road weather situations, FHWA sponsors several initiatives including:
The Clarus Initiative (no, this isn't a Robert Ludlum novel). This project is designed to enable public agencies to more accurately assess weather and pavement conditions as well as the impacts on operations so they can improve planning, conducting, and evaluating the effectiveness of activities such as winter road maintenance. The Clarus website tracks related research in the several participating states .
Maintenance Decision Support System (MDSS). FHWA recognizes that controlling snow and ice buildup on roadways during winter weather events presents challenges for winter maintenance personnel, particularly the need to make effective winter maintenance decisions (treatment types, timing, rates, and locations). Several participating states are testing an ever-improving computerized system where the agency inputs its strategic priorities and its road weather data and receives a customized tactical plan for each storm as it emerges. Check for the latest developments .
State highway agencies carry the brunt of the war against winter weather on our superhighways and arterial roads. The American Association of State Highway and Transportation Officials (AASHTO) has an active snowfighting program (its training materials are described in our Education Center). Among AASHTO initiatives are:
The Snow and Ice Pooled Fund Cooperative Program (SICOP)
The Aurora Program which focuses on improving road weather integration with snowfighting (RWIS systems)
In addition, the Clear Roads program, a pooled fund research project run by the Wisconsin DOT undertakes testing of winter maintenance materials, equipment and methods for use by highway maintenance crews.
The Transportation Research Board also administers the National Cooperative Highway Research Program (NCHRP) which has produced snowfighting performance analyses (an example). TRB also sponsor quadrennial Symposia on Snow Removal and Ice Control Technology , the most recent of which was held in June 2008 where several papers examined snowfighting's role in improving highway operations.
In Canada, the Transportation Associaton of Canada produced a road salt Code of Practice , recast as Syntheses of Practice , outlining consensus expectations of Canadian snowfighters. Environment Canada has embraced the TAC guidelines in its Road Salts Code of Practice .
For a spot-on summary, read Alan Gesford's "10 Lessons for Winter Operations Survival " in Better Roads magazine. Better Roads' editor-in-chief Ruth Stidger also has a feature on "The Basics of Salting and Sanding " that remains a solid, if brief, primer.
For good, practical and timely information, make a regular visit to The Winter Maintenance Podcast run by Dwayne Collett.
Transparency and accountability in snowfighting.
Mentioned above under "Roadway operations" are some of the efforts being undertaken to focus road agencies on producing desired outcomes, measuring outcomes instead of either inputs or outputs. Some states and cities are laying the groundwork for even greater public accountability by web-posting their plans and results. That allows citizens to determine if they should insist on higher service levels and enables them to judge whether their tax dollars are achieving the promised outcomes. Here are some examples:
And check out the same effort in Sapporo, Japan
Agencies are not alone in judging their effectiveness. The Illinois Policy Institute has produced a report on how citizens assess snowfighting performance.
- FHWA has a road weather program for rural highways, FORETELL.
- North Dakota has produced an evaluation report on "integrated road weather information"
- Meteorologists are discovering "road weather" is important, not just atmospheric forecasting
- Many states and provinces' transportation agencies put traffic cameras online so citizens can see weather and road conditions (example, Newfoundland )
Preserving safe driving conditions and commerical mobility is not a new concept. International Salt Company ran this print ad back in the 1930s. The latest snowfighting technique is "anti-icing." But is it so new? Anti-icing was common practice as long ago as the 1930s. The National Snow and Ice Data Center at the University of Colorado has an easy-to-read short history of U.S. snowfighting, "Have Snow Shovel, Will Travel ." Capture the flavor of life as an early snowfighter in this podcast by Dwayne Collett.