Road salt

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An Econ-brand salt spreader spreading salt on a road during the 2010 UK winter. Econ Salt Spreader.jpg
An Econ-brand salt spreader spreading salt on a road during the 2010 UK winter.

Road salt (also known as de-icing salt, rock salt, snow salt or grit salt) is a salt used mainly as an anti-slip agent in winter road conditions, but also to prevent dust and snow build-up on roads. [1] Various kinds of salts are used as road salt, but calcium chloride and sodium chloride (rock salt) are among the most common. [2] [3] The more expensive magnesium chloride is generally considered safer, but is not as widely used because of its cost and effect on structural integrity. [4] [5] When used in its solid form, road salt is often pre-wet to accelerate the ice-melting process. [6] Road salts have been having adverse effects on the environment, including decreasing biodiversity, contaminating of water sources, and increasing soil salinity.

Contents

History

The use of salt for snow and ice control began in the early 20th century. In Paris, sodium chloride was applied on a large scale to combat black ice, [7] although the practice soon revealed disadvantages such as corrosion of iron structures and damage to the hooves of draft animals. Despite these drawbacks, the method proved effective in improving road safety and was soon adopted in other cities and countries.

The use of salt for deicing roads began in the United States in the late 1930s, when New Hampshire experimented with spreading granular sodium chloride on roads in 1938. [8] [9] [10] By the winter of 1941–1942, New Hampshire formally adopted a statewide salt-spreading policy; about 5,000 tons of salt were applied on U.S. highways that season. Before the adoption of road salt in New Hampshire, road maintenance in winter typically relied on plowing and spreading abrasives (sand, cinders) for traction, with salt only used occasionally (e.g. to slow freezing in stored sand piles). [11]

Road salt storage depot in Lamure-sur-Azergues (Rhone, France). Lamure-sur-Azergues - Depot de sel pour les routes (mars 2019).jpg
Road salt storage depot in Lamure-sur-Azergues (Rhône, France).

In the post-war era, as the U.S highway networks expanded and the “bare pavement” standard (expectation that roads be cleared quickly) became dominant, salt usage increased greatly. During the 1950s and 1960s, U.S. salt consumption doubled roughly every five years, climbing from about 1 million tons in the mid-1950s to nearly 10 million tons less than a decade later. Supply sources developed along with the demand, large underground rock-salt deposits (formed by the evaporation of ancient seas) supplied much of the salt. The Detroit salt mine (first discovered in 1895) became a prominent example as the mines expanded over the 20th century and supported local deicing operations. Detroit itself was among the earliest cities to apply salt to its roads (circa 1940) believed to be due to its proximity to the resource. [12]

A parallel development occurred in Europe. In Germany, salt spreading became common in the 1960s as motorization increased and road safety demands grew. [13] [14] Authorities established salt storage facilities and distributed salt manually from trucks before mechanical spreaders were introduced to improve efficiency. The transition from dry to wet-salt application in the early 1970s represented a further advancement, as prewetted salt adhered better to road surfaces and was less susceptible to wind displacement.

In later decades, salt use stabilized (on the order of tens of millions of tons per year in the U.S.), and attention has shifted to optimizing application methods and mitigating collateral impacts. [15] More recently, occasional supply constraints and environmental concerns have spurred experimentation with reduced-salt strategies and alternative deicers (e.g. prewetting, salt–organic blends, calcium or magnesium salts). [1]

Storage tank for road salt in Puente de los Hocinos, Spain. Road salt storage - N211- Teruel, Spain.jpg
Storage tank for road salt in Puente de los Hocinos, Spain.

Spreading

Road salt and brine are generally spread using a winter service vehicle called a salt spreader. Salt spreaders are typically added to trucks, loaders, or in the case of brine, tankers. The salt is stored in the large hopper on the rear of the vehicle, with a wire mesh over the top to prevent foreign objects from entering the spreading mechanism and hence becoming jammed. The salt is generally spread across the roadway by an impeller, attached by a hydraulic drive system to a small onboard engine. However, until the 1970s, it was often spread manually either by workers shoveling salt from trucks or by smaller wheelbarrow-like vehicles, the latter still being used today for personal use. [16] Some older spreading mechanisms still require it to be manually loaded into the impeller from the hopper.

Mechanics

Salt for use of melting ice and snow works through a phenomenon called freezing-point depression, the lowering of a substance's freezing point after the addition of solutes. When road salt is added to roads, aside from providing better friction for vehicles on the road, it also dissolves in the water of the ice, resulting in a lower freezing point. As long as the temperature is above this freezing point, this in turn results in the ice melting. [17] [18] Because of this, ordinary rock salt is only effective down to a range of −6 to −10 °C (21 to 14 °F). At colder temperatures, it can have the opposite effect. Road salt is sometimes used even in colder conditions, if milder weather is expected. In very cold and dry weather, the road surface becomes rough and the need for de-icing is reduced. However, during extreme cold and rain, the roads can become extremely difficult to pass and, in some cases, roads may need to be closed to traffic. [19]

Types of salt

Various types of salts. (T–B): Sodium Chloride, Calcium Chloride, Magnesium Chloride.
Chlorid sodny.JPG
Chlorek wapnia bezw 1.jpg
Salt of Sodom IMG 97692.JPG

Sodium chloride

Sodium chloride is by far the most common kind of road salt. This is mainly due to its widespread use and low cost, and thanks to its large industrial infrastructure, [20] it is used in many industrial and consumer applications. [21] While it is common and inexpensive, its effective temperature range usually does not fall below −6 to −10 °C (21 to 14 °F), and under these temperatures, it is often counter-productive. When used in large quantities, it can also disrupt local ecosystems by heightening the salinity of bodies of water and the soil. Further, rock salt's abrasive nature erodes concrete or asphalt if used heavily. [22] [23]

Calcium chloride

Calcium chloride is less common compared to sodium chloride. While it is slightly more expensive, it can cover a far larger area and melts ice almost three times quicker. [24] It has recently started rising in popularity since it is not as environmentally damaging as sodium chloride, and also because of its heightened effectiveness at clearing ice. [25] [26]

Magnesium chloride

Magnesium chloride is more expensive by far than the road salts in common use today. It has a very low environmental impact, and is quite effective at clearing ice. However, it has been discovered that magnesium chloride causes far more damage to concrete surfaces compared to the other salts, and its use as a de-icing chemical has largely been discontinued. [4] [5] It is still widespread as a highly effective dust clearer in warmer weather. [27]

Environmental impact

The widespread use of road salt has significant environmental and infrastructural repercussions. While effective and relatively inexpensive, this practice incurs hidden costs because of its corrosive nature, leading to approximately $5 billion in annual repairs across the United States, according to the country's Environmental Protection Agency. [1]

One of the primary environmental concerns is the contamination of water sources. As road salt works through dissolving in snow and ice, and thereby lowering its melting point, the salt stays dissolved as the snow melt funnels into storm drains. These storm drains then lead into the sewer system, which washes into rivers, lakes and other bodies of water. [1] Due to high levels of road salt runoff, these bodies of water can suffer freshwater salinisation, which results in numerous environmental consequences. When salinisation becomes widespread, it leads to a decrease of in-lake water levels, overuse of water in the drainage basin, encouragement of global climate change and reduced biodiversity. [28] It is clear that high levels of chloride, an ion present in most common, inorganic road salts, are toxic to fish, amphibians, and macroinvertebrates. These salt levels could result in the extirpation of freshwater species in salinated bodies of water. The increase of salt concentrations in drinking water could also be affected, as the salt not only permeates rivers and lakes, but the ground water as well. Water starts to taste salty when chloride concentrations exceed 250 mg/L. [29] This elevated salt level could also lead to various elecrolyte imbalances, especially hypernatremia, in people who consume the salinated tap water. This in turn can cause symptoms such as, thirst, weakness, nausea, and loss of appetite, and more severely, confusion, muscle twitching, and bleeding in or around the brain. [30]

Road salts also contribute to the process of water eutrophication. It is the process by which nutrients such as nitrogen and chloride rapidly accumulate in water. As a result, these nutrients support the overgrowth of organisms such as algae and create algal blooms. The death of these overgrown algae and algal blooms causes a depletion in oxygen in the water when they decompose, which can kill and harm various aquatic life in the waters. Furthermore, these conditions create a positive feedback loop where it the death of algae continue to create conditions that are favorable for algae to grow in, leading to greater and greater damage. [31]

The accumulation of salt in roadside soils adversely affects vegetation by increasing soil salinity, which can hinder plant growth and lead to the death of sensitive species. This degradation of plant life not only disrupts local ecosystems but also contributes to soil erosion. Additionally, wildlife attracted to the salt (such as deer and moose) can be endangered, as they may ingest harmful amounts or be drawn to roadways, increasing the likelihood of vehicle collisions. The term "Salt Belt" refers to regions with heavy road salt usage, predominantly in the northeastern United States. In these areas, the cumulative effects of salt application are more pronounced, leading to higher concentrations of salt in the environment and exacerbating the associated negative impacts.

Alternatives

Alternatives to traditional road salt are being explored to mitigate its environmental and infrastructural damage. While magnesium chloride and calcium chloride are considered less harmful to the environment, they are more expensive and may require higher application rates. Other strategies that help reduce salt usage and discharge into waterways include spraying road surfaces with brine in anticipation of snowfall, as well as mixing salt with other substances such as sand to improve traction, dyes to aid in identification of salted areas, [32] and biodegradables like beet juice, pickle juice, and molasses. [33] Innovative solutions, such as porous pavements, have also been developed to reduce ice accumulation and minimize the need for de-icing agents.

Although certain scientists propose these biodegradable solutions to be more environmentally friendly than road salts, some studies suggest that they may be more detrimental to certain essential aquatic species such as zooplankton. Zooplankton serve as one of the main sources of food for smaller fish, and are essential in making sure that energy transfer from different trophic levels occurs smoothly in the food web. Further investigation and research is still required before these alternatives can be successfully implemented. [34] The following lists contains the most-commonly used de-icing chemicals and their typical chemical formula.

Salt

Organics

See also

References

  1. 1 2 3 4 Sherwell, Shasten (2020-11-01). "Winter is Coming! And with it, tons of salt on our roads" (Government Report). U.S. Environmental Protection Agency. Post Office Square, Boston, Massachusetts, United States of America: United States Environmental Protection Agency. Archived (PDF) from the original on 2025-09-20. Retrieved 2025-10-28.
  2. ↑ Rasevic, Paul (2018-10-12). "Comparing Calcium Chloride vs Sodium Chloride for Melting Ice and Snow". Snow & Ice Salt & Chemicals Unlimited, LLC (Business Article). Doctor Perry Road, Ijamsville, Maryland, United States. Archived from the original on 2025-03-24. Retrieved 2025-11-08.
  3. ↑ Murphy, Dan (2012-10-14). "Calcium Chloride vs. Rock Salt. Which do you use?". Peters Chemical Company (Business Article). Hawthorne, New Jersey, United States. Archived from the original on 2024-10-07. Retrieved 2025-10-08.
  4. 1 2 Peters Chemical Company. "Magnesium Chloride As A Road Deicer: A Critical Review". Peters Chemical Company (Business Article). Hawthorne, New Jersey, United States. Archived from the original on 2012-06-14. Retrieved 2024-10-04.
  5. 1 2 Saltimport AS (2024-03-01). "Magnesiumklorid er et mindre effektiv veisalt enn kalsiumklorid" [Magnesium Chloride is a less effective road salt than Calcium Chloride]. www.salt.no (Business Website) (in Norwegian). Sandviksveien, Bergen, Norway. Archived from the original on 2024-08-15. Retrieved 2024-10-04.
  6. ↑ SnowEx (2025-01-12). "The Trend of Pre-Wetting". SnowEx. Madison Heights, Michigan, United States: Douglas Dynamics, LLC. Archived from the original on 2025-08-15. Retrieved 2025-11-10.
  7. ↑ Lueger, Otto (1910). Lexikon der gesamten Technik und ihrer Hilfswissenschaften[Encyclopaedia of Technology and Auxiliary Sciences] (in German) (2nd ed.). Stuttgart, Württemberg, German Empire: Deutsche Verlags-Anstalt. pp. 358–361.
  8. ↑ R. Kelly, Victoria; E. G. Findlay, Stuart; H. Schlesinger, William; Menking, Kirsten; Morrill Chatrchyan, Allison (2010) [December]. "Road Salt: Moving Toward the Solution" (PDF) 2801 Sharon Turnpike, Millbrook, New York State, United States of America (Special Report). Cary Institute of Ecosystem Studies: 16. Retrieved 28 October 2025.
  9. ↑ Transportation Research Board. "Road Salt Use in the United States" (PDF). Transportation Research Board Online Publications. Fifth Street NW, Washington, D.C., United States of America. Archived (PDF) from the original on 2025-08-27. Retrieved 2025-11-10.
  10. ↑ Plumer, Brad (2015-01-25). "How America got addicted to road salt — and why it's become a problem" . Vox (Newspaper Article). Washington, D.C., United States of America. Archived from the original on 2025-08-27. Retrieved 2025-11-10.
  11. ↑ Howard, Brian Clark (2014-02-14). "The Surprising History of Road Salt". National Geographic (Newspaper Article). Washington, D.C., United States of America: National Geographic Society. Archived from the original on 2025-09-13. Retrieved 2025-11-10.
  12. ↑ The Detroit News (2020-01-26). Miles, Gary (ed.). "Detroit's salt mine: City beneath the city". The Detroit News. West Lafayette Boulevard in Detroit, Michigan, United States of America. Archived from the original on 25 Nov 2025. Retrieved 2025-11-10.
  13. ↑ Georg, Josef (2001). Der Straßenwärter Früher und Heute [Road Maintenance Then and Now] (in German). Norderstedt: Books on Demand. ISBN   9783831119998.
  14. ↑ Haaf, Günter (1979-11-30). "Bäume sterben langsam" [The Trees Die Slowly]. Die Zeit (Newspaper Article) (in German). No. 49. Hamburg, Germany: Zeitverlag Gerd Bucerius. ISSN   0044-2070. Archived from the original on 2023-04-13. Retrieved 2025-11-10.
  15. ↑ MacBlane, Beth (2024). Magin, Amy (ed.). "Hold the Salt: Reducing Winter Salt Application" (PDF). Interstate Waters Magazine (Trade Magazine Article). Vol. 8, no. 1. Suffolk Street, Lowell, Massachusetts, United States of America: New England Interstate Water Pollution Control Commission. pp. 9–11. Archived (PDF) from the original on 2025-03-19. Retrieved 2025-11-10.
  16. ↑ Snow Trading SRL. (2023-10-04). "WB Walk Behind Spreaders". Snow Trading. Via Caduti senza Croce, Baggiovara Modena, Italy. Archived from the original on 2025-05-16. Retrieved 2025-11-10.
  17. ↑ HowStuffWorks.com (2023-09-08). "Why Does Salt Melt Ice on the Roads in Winter?". HowStuffWorks (Pop-Science Article). Redwood Avenue, Marina Del Rey, California, United States of America: System1. Archived from the original on 2025-09-29. Retrieved 2025-11-10.
  18. ↑ Pollock, Julie; The Conversation (2019-02-12). Ewalt, David M. (ed.). "Salt Doesn't Melt Ice—Here's How It Makes Winter Streets Safer". Scientific American (Pop-Science Article). New York Plaza, New York, New York State, United States of America. Archived from the original on 2025-06-14. Retrieved 2025-11-10.
  19. ↑ Trafikverket (2024-09-23). "Vägsalt - bara där det behövs". Trafikverket (Government Article) (in Swedish). Röda vägen, Borlänge, Dalarna, Sweden. Archived from the original on 2025-07-09. Retrieved 2025-11-10.
  20. ↑ Morton Salt, Inc. (2016-03-05). "Salt Production and Processing". Morton Salt (Business Article). Overland Park, Kansas, United States. Archived from the original on 2025-09-30. Retrieved 2025-11-10.
  21. ↑ Mowat, Anna (2016-09-27). "The Hidden Costs of Road Salt". Adirondack Research (Research Blog). Adirondack Research, Church Street, Saranac Lake, New York State, United States of America. Archived from the original on 2025-01-25. Retrieved 2025-11-10.
  22. ↑ Sherwell, Shasten (2020-11-01). "Winter is Coming! And with it, tons of salt on our roads". United States Environmental Protection Agency (Government Article). New England, United States. Archived from the original on 2025-10-08. Retrieved 2024-11-08.
  23. ↑ Rollin, Justin (2024-04-08). "What Type of Salt Is Used on Roads?". Ninja De-Icer (Business Article). Bellevue St Suite D, Green Bay, Wisconsin. Archived from the original on 2025-05-20. Retrieved 2025-11-10.
  24. ↑ Eco Living Situations (2020-09-26). "Should you use calcium chloride on roads?". Eco Garden Solutions (Business Article). Alicia Pkwy, Laguna Niguel, California, United States of America. Archived from the original on 2025-01-25. Retrieved 2025-11-10.
  25. ↑ Peters Jr., Harold V. "Road Treatment – Information About Calcium Chloride". Peters Chemical Company. Hawthorne, New Jersey, United States. Archived from the original on 2025-04-09. Retrieved 2025-11-10.
  26. ↑ "Calcium Chloride versus Rock Salt". Snow & Ice Salt & Chemicals Unlimited (Business Article). Doctor Perry Road, Ijamsville, Maryland, United States. 2022-06-27. Archived from the original on 2025-01-25. Retrieved 2025-11-10.
  27. ↑ Substrata, LLC. (2024-04-26). "What Is Magnesium Chloride, and What's It Used for?". Substrata (Business Article). Eastgate Rd, Henderson, Nevada. Archived from the original on 2025-08-06. Retrieved 2025-11-10.
  28. ↑ Jørgensen, S.E (2008-08-06). "Freshwater Lakes". In Fath, Brian D.; Jørgensen, Sven Erik (eds.). Encyclopedia of Ecology (1st ed.). Copenhagen University, Faculty of Pharmaceutical Sciences, Copenhagen, Denmark: Elsevier Science. pp. 1686–1689. ISBN   978-0-08-045405-4. Archived from the original on 2012-03-19. Retrieved 2025-11-25.
  29. ↑ Rodbarry, Lea (2023-12-10). "From Streets to Streams: The Impact of Road Salt on the Environment". The Conservation foundation (Non-profit Organisation Article). McDonald Farm, Knoch Knolls Road, Naperville, Illinois, United States of America: The. Archived from the original on 2025-02-14. Retrieved 2025-11-25.
  30. ↑ Sonani, Bhavin; Naganathan, Srividya; Al-Dhahir, Mohammed A. (2023-08-24). "Hypernatremia". StatPearls [Internet]. Treasure Island, Florida, United States of America: StatPearls Publishing. Archived from the original on 2025-09-05.
  31. ↑ Szklarek, Sebastian; Górecka, Aleksandra; Wojtal-Frankiewicz, Adrianna (2022-01-20). Gan, Jay; Hopke, Philip; Ouyang, Wei; Paoletti, Elena (eds.). "The effects of road salt on freshwater ecosystems and solutions for mitigating chloride pollution - A review" . Science of the Total Environment (Review). 805 150289. Elsevier. Bibcode:2022ScTEn.80550289S. doi:10.1016/j.scitotenv.2021.150289. Archived from the original on 23 Dec 2024. Retrieved 2025-11-10– via Science Direct.
  32. ↑ Canada Salt Group Ltd. (2020-10-30). "Why Road Salt Is Blue?". Canada Salt (Business Article). Markham, Ontario, Canada. Archived from the original on 2025-09-09. Retrieved 2025-11-10.
  33. ↑ Casey, Michael (2018-01-29). "Turning to beet juice and beer to address road salt danger". Phys.org (Scientific News Article). Hope St, Douglas, Isle of Man: Science X. Archived from the original on 2025-09-25. Retrieved 2025-11-10.
  34. ↑ Fee, Abigail; Martin, Troy; Cicchetti, Lisa; Manoel, Pedro S.; Arnott, Shelley E. (2025-07-31). Burton, Jr., G.A. (ed.). ""Eco-friendly" road deicers may not be so friendly: assessing the toxicity of beet-juice brine and potassium chloride to Daphnia pulicaria" (PDF). Environmental Toxicology and Chemistry (Journal Article). 44 (8). Wiley-Blackwell (published 25 April 2025): 2089–2097. doi: 10.1093/etojnl/vgaf110 . ISSN   0730-7268. PMID   40279480. Archived (PDF) from the original on 2025-11-10 – via Oxford Academic.
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