From Wikipedia, the free encyclopedia - View original article
Snow removal is the job of removing snow after a snowfall to make travel easier and safer. This is done by both individual households and by governments and institutions.
De-icing is defined as removal of existing, snow ice, frost, etc., from a surface. It includes both mechanical (plowing or scraping) or chemical (application of salt or other ice melting chemicals) methods.
Anti-icing is defined as the pretreatment of a roadway, sidewalk or parking lot with ice melting chemicals before a storm, to prevent or delay the formation of ice, or the adhesion of ice and snow. Brine or wetted salt is usually applied shortly before a snowstorm arrives. Properly performed, anti-icing can significantly reduce the amount of salt required, and allows easier removal by mechanical methods (snowplows).
De-icing of roads has traditionally been done with salt, spread by snowplows or dump trucks designed to spread it, often mixed with sand and gravel, on slick roads. Sodium chloride (rock salt) is normally used, as it is inexpensive and readily available in large quantities. However, since salt water still freezes at −18 °C or 0 °F, it is of no help when the temperature falls below this point. It also has a strong tendency to cause corrosion, rusting the steel used in most vehicles and the rebar in concrete bridges. More recent snowmelters use other salts, such as calcium chloride and magnesium chloride, which not only depress the freezing point of water to a much lower temperature, but also produce an exothermic reaction. They are somewhat safer for concrete sidewalks, but excess should still be removed.
More recently, organic compounds have been developed that reduce the environmental issues connected with salts and have longer residual effects when spread on roadways, usually in conjunction with salt brines or solids. These compounds are generated as byproducts of agricultural operations such as sugar beet refining or the distillation process that produces ethanol. Additionally, mixing common rock salt with some of the organic compounds and magnesium chloride results in spreadable materials that are both effective to much colder temperatures (−30 °F/−34 °C) as well as at lower overall rates of spreading per unit area.
Since the 1990s, use of liquid chemical melters has been increasing, sprayed on roads by nozzles instead of a spinning spreader. Liquid melters are more effective at preventing the ice from bonding to the surface than melting through existing ice.
Several proprietary products incorporate anti-icing chemicals into the pavement. Verglimit incorporates calcium chloride granules into asphalt pavement. The granules are continually exposed by traffic wear, and release calcium chloride onto the surface. This prevents snow and ice from sticking to the pavement  Cargill SafeLane is a proprietary pavement surface treatment that absorbs anti-icing brines, to be released during a storm or other icing event. It also provides a high-friction surface, increasing traction.
In Nagano, Japan, relatively inexpensive hot water bubbles up through holes in the pavement to melt snow, though this solution is only practical within a city or town. Some individual buildings may melt snow and ice with electric heating elements buried in the pavement, or even on a roof to prevent ice dams under the shingles, or to keep massive chunks of snow and dangerous icicles from collapsing on anyone below. Small areas of pavement can be kept ice-free by circulating heated liquids in embedded piping systems.
Most snow removal by individuals is clearance of driveways and walkways. After heavy snowfalls, snow may be removed from roofs to reduce the risk of structural damage due to the weight.
In places with light snow, brooms or other light instruments can be used to brush off snow from walks and other surfaces. In regions with more precipitation, snow is commonly removed with snow shovels, a large lightweight shovel used to push snow and lift it, and snow scoops or sleigh shovels, a large and deep hopper-like implement fitted with a wide handle and designed to scoop up a load of snow and slide it on any slippery surface to another location without lifting. Other tools include snow pushers and shovels with one or more wheels.
Shovelling entails a considerable amount of physical effort and can strain the back and the heart. Each year many senior citizens and middle aged persons die from heart attacks while shovelling snow.[not in citation given]
Snow blowers are often used by people unwilling or unable to perform this labour, people with large driveways or other substantial surfaces and people who live in areas with long lasting winters with large amounts of snowfall. Others may hire a contractor with a plow bearing truck or a shovel. After a large snowfall, businessmen with plow trucks often drive through cities offering to plow for money.
Removing ice is more difficult. Snow blowers are usually ineffective for clearing ice. Picks are sometimes used, but a solid spade can break through most ice. There is always the risk of damaging the pavement with these instruments. Icy areas can be covered with salt or some other substance, bags of which are widely available.
A recent technological advance is the snowmelt system that heats the pavement from below and melts snow and ice after a period of time. Such systems are expensive to install and operate and they are not cost effective in areas with very low winter temperatures and large snowfalls.
Some governments offer free snow clearing for the elderly and others in need. In some cities, snow clearing for elder and handicapped residents counts towards community service hours assigned as a punishment for minor offences.
In many places, laws require homeowners to clear snow from the public sidewalk in front of their house, as well as a pathway on their own property to their mailbox. Those who fail to do so, depending on the jurisdiction's laws, may face fines and may be civilly liable for injuries suffered by another on a surface that they were required to clear. In some jurisdictions, such as New York, private home owners who shovel are held civilly liable for others' injuries incurred by falling in areas that have been shovelled.
Cleaning off and freeing one's vehicle is another matter. Many people who need their vehicles will do just barely what is necessary in order to drive the vehicle and remove it from its space. Failure to clear all the snow and ice off a vehicle causes hazards by restricting the driver's visibility, and ice from the roofs of driven vehicles can cause crashes. In some jurisdictions, motorists who fail to completely clean snow off their vehicle can be fined. Others may be more thorough in this process.
In some countries, to ensure the winter trafficability of sidewalks belongs to duties of the owner of the contiguous land or building. Such owner can be an individual inhabitant, in case of a family house, but also the municipality, municipal district or their specific organization or a housing co-operative or some other company (especially if some office or industrial object is concerned). Owners of large buildings or building complexes generally have mechanized snow-removal equipment, but individual house owners mostly clean the sidewalk with hand tools.
For example, in Prague, a persistency of such duty is documented since 1838. The decree of the government of Protectorate of Bohemia and Moravia No 1/1943 Sb. said that sidewalk cleaning in residential area in municipalities with more than 5000 inhabitants, district cities and other specified municipalities is a duty of the owner or user of the contiguous land. The municipality was empowered to undertake this duty at the expense of the contiguous land owner. The Czechoslovak Road Act No 135/1961 Sb. (§ 23) adopted such legal regulations for all municipalites, but municipality offices might modify them. The new Road Act of the Czech Republic, No 13/1997 Sb. (§ 9 art. 4) left this enactment and stated that way maintenance is an obligation of the way owner, without any exception. Despite of it, § 27 art. 4 attached to the contiguous land owner the liability for harm caused by defects of cleaning. The Czech Public Defender of Rights claimed in 2002 and 2003 annual reports the discrepancy between theoretical and practical interpretations of the act and recommended to enact an unequivocal formulation. This discrepance was repeatedly handled by courts and the Supreme Administrative Court on 2005 June 27 and the Constitutional Court on 2007 January 3-rd stated that the cleaning duty results indirectly from the stated liability for harm. Impugners of the duty argued that this duty is a residue of feudal corvée or of totalitarian nazism and communistic regimes and that nowadays, compulsory labour at extrinsic way is in conflict with Charter of Fundamental Rights and Basic Freedoms, and that systematic municipal cleaning is more effective than a cleaning by individuals. On December 6, 2007, the Senate of the Czech Republic proposed at the instance of its Constitutional Committee to let out the controversial article. The Czech Government give support to it by their narrow majority. Past heated debate, the Chamber of Deputies of the Czech Republic sanctioned this change by 116:31 ratio from 190 presenting members. Since 2009 April 16-th, the change made by the act No 97/2009 Sb. is forcing and sidewalk cleaning is an obligation of the sidewalk owner only, i. e. generally the municipality. In despite of duty abolition, many people including oppugnants of the duty declared that they will to continue the winter cleaning of municipal sidewalks, but voluntarily and on their own behalf.
As was mentioned during the discussion at the Czech Parliament by the statement of the Czech Association of Cities and Municipalities, similar duty remains in many other modern countries, e. g. Austria, France and some cities of Bavaria and USA.
Hiring a contractor with a winter service vehicle or a shovel.
In many high elevation or heavy snow accumulating areas, companies with snow removal equipment offer to provide services to remove the snow. Contractors may work on a per-time basis, full season contract, or will-call status. Per-time service (or per-push) is usually invoiced monthly and customers will be charged for each time services are provided. Some companies will charge per-time and per-inch where the depth of the snow is even taken into account. A full season contract is quoted and paid upfront at the start of the season and services will be provided automatically according to the contracted terms. All companies have different terms so make sure to understand the agreement. For example, some full season contracts will expire after X amount of trips where others are unlimited. And finally, will-call service is where the client makes contact with the snow removal company to initiate a single clearing. This is not an automatic service and charges are usually higher for will-call jobs.
Snow removal services may include driveway and parking area snow removal, walkway and deck handwork, and occasionally roof clearing. Contractors use hand shovels, walk behind snowblowers (or snow throwers), truck plows, skid-steers, light-weight tractors, and heavy front-end loaders. Many times, these machines will require use of tire chains to perform their tasks. Snow may be pushed by plowing methods or blown to an area of the property by snowblowers. Contracts may apply sand or salt in some locations to help melt ice accumulations.
Many snow removal contractors will require installation of snow poles or snow staking along the driveway. This is to keep equipment out of the landscaping and to help identify the perimeter of an area.
Contractors should be licensed and insured.
Cities clear snow on a much larger scale than individuals. Most cities in areas that get regular snowfall maintain a fleet of snow clearing vehicles. The first to be dispatched are gritters who do some plowing but also salt the road. The salt, via freezing point depression, helps melt the snow and ice and also gives vehicles more traction. Later, usually when the snow has ceased falling, snow plows, front end loaders with snowplow attachments and graders cover every street pushing snow to the side of the road. Salt trucks often then return to deal with any remaining ice and snow. The trucks generally travel much faster than the plows, averaging between 30 and 40 kilometers per hour. Most cities thus have at least twice as many plows as trucks. Smaller narrow body plows, with Caterpillar tracks or huge snow tires salt and clear sidewalks in some cities, but in many others with less snowfall and/or less pedestrian traffic individuals are tasked with clearing the sidewalk in front of their homes. Ecological movements often oppose this use of salt because of the damage it does when it eventually washes off the roads and spreads to the environment in general.
In cities where snow steadily accumulates over the winter it is also necessary to remove the piles of snow that build up on the side of the roads known as windrows or snowbanks. There are a number of methods of doing this. Pulling snow is done when temperatures rise high enough for traffic to melt snow. The windrows are then broken up and spread over the road. Casting is the moving of snow by means of a shovel or plow to nearby public lands. On boulevards or highways winging back is done, which consists of pushing the snow banks further from the road. The most expensive option, but necessary when there are no nearby places to dump the snow, is to haul it away. This is most often done by large self-propelled snowblowers that gather the piles of snow at the side of the road and load it into dump trucks. The snow is then dumped on the outskirts of town, or in a nearby lake, river or harbor. (Some jurisdictions have banned dumping snow into local bodies of water for environmental reasons - modern roads can be contaminated with melting salt, motor oil, and other substances.) Snow melting machines may be cheaper than moving snow, depending on the cost of fuel and the ambient temperature.
The windrows created by the plows in residential areas often block driveways and imprison parked cars. The snow pushed there by any plow is a dense, packed version of "normal" fallen snow. When the temperatures are significantly below freezing this packed snow takes some of the characteristics of solid ice. Its removal is nearly impossible without mechanical means.
The largest roads and highways are the first to be cleared; roads with steep hills or other dangers are also often a priority. Streets used by buses and other mass transit are also often given higher priorities. It often takes many hours, or even days, to cover every street in a city. In some places, a snow emergency will be declared, where automobile owners are instructed to remove their vehicles from the street (or one side of a street). If cars are in the way when the plows come around, they may be hauled away by tow trucks. Some communities have standing snow emergency rules in winter, in which vehicles may not be parked on streets overnight, whether it snows or not. After smaller snow storms only main roads are cleared while residential ones are left to be melted by passing traffic. Decisions on immediate removal versus "natural melting" can be hard to make because the inconvenience to citizens and the economy in general must be weighed against the immediate effect on the snow removal budget at that particular moment in the season.
In large cities with heavy snowfalls like Montreal and Ottawa, the snow clearing expense for each season is an important part of the seasonal public works budget and each snow storm provokes a major logistical operation involving thousands of employees working in shifts 24 hours a day. The effort can vary greatly depending on the amount of snow. Montreal gets about 225 cm of snow each winter and spends more than $158 million Canadian (2013) each year to remove it. Toronto, with about 50 per cent more population and 28 per cent more road surface, gets only 125 cm of snow a year and spends about half that. The higher cost in Montreal is due to the need to perform "snow removal" as opposed to simple "snow clearing" necessitated by both the high snowfall amounts and fewer melting days.
Snow removal impacts the design of city infrastructure. Where possible, street boulevards are wider to accommodate the windrows and sidewalks are not right next to the street. Fire hydrants will have tall flags to locate them under the windrows. Reflective traffic lane markers embedded in the roadbed is not possible (or much harder) due to risk of damage by plows. Access to snow dumping locations (e.g. ravines) by heavy equipment is also planned.
It is estimated that Canada spends $1 billion on snow removal. The employees who do this work are generally the same workers who do road maintenance work during the summer months, but in some US cities garbage trucks are also equipped with plows and used for snow removal. Many smaller US communities sign contracts with insurance companies, under which the insurance company assumes the risk of a heavy winter. The insurance company of course sets the rates such that averaged over time they will make a profit; the town is willing to overpay for snow removal in mild winters in order to avoid the risk of running dramatically over budget in the occasional severe winter.
Large organizations such as universities and airports also often have their own mechanized snow clearing force. Public transit systems generally clear bus stops while post offices clear around mail boxes. Railroads have their own snow clearing devices such as rotary snowplows.
Airports, with their associated runways, taxiways and ramp areas are an exception to the use of salt, as the metals used in aircraft construction will corrode causing safety issues.
The surface is treated primarily by snow removal. Roads are also treated by spreading various materials on the surface. These materials generally fall into two categories: chemical and inert. Chemical (including salt) distribution induces freezing-point depression, causing ice and snow to melt at a lower temperature. Chemical treatment can be applied as a preventive measure and/or after snowfall. Inert materials (i.e. sand, brash, slag) make the surface irregular to improve traction. Both types can be applied together, but the inert materials tend to lower traction once the snow and ice has melted.
Chemical treatment materials include:
In the European Union, ca 98% of chemical treatment materials used in 2000 were sodium chloride in various forms. It is effective down to −5 °C, at the most −7 °C. For colder temperatures, calcium chloride (CaCl2) is added to NaCl in some countries, but deployment is limited as it costs about 6 times as much as sodium chloride. Other substances were used rarely and experimentally. Alternative substances (urea, alcohols, glycols) are often used at airports. In recent years, Geomelt, a combination of salt brine and beet juice that is otherwise considered a waste product has been used for pretreatment.
Inert spreadings can be:
The choice of treatment may include consideration of the effect on vegetation, pets and other animals, the local watershed, and effectiveness with regard to speed and temperature. Some chemicals can degrade concrete, metals, and other materials. The resulting meltwater and slush can cause frost heaving if it re-freezes, which can also damage pavement. Inert materials can damage vehicles and create dust.
As an example, in the Czech Republic during the winter season of 2000/2001, net material expenditure for road treatment was: 168 000 tonnes of salt (mostly NaCl), 348 000 tonnes of sand and crushed stone and 91 000 tonnes of other materials like slag. In Ireland, the annual expenditure of salt was 30 000 tonnes. Switzerland reports their annual expenditure as 600 grammes of salt to every square metre of roads on average.
|Wikimedia Commons has media related to: Snow removal|