Road slipperiness is a condition of low

skid __NOTOC__ Skid or Skids may refer to: * Skid, a type of pallet * Skid (aerodynamics), an outward side-slip in an aircraft turn * Skid (automobile), an automobile handling condition where one or more tires are slipping relative to the road * Skid ...

resistance due to insufficient road friction. It is a result of

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...

, ice,

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

, loose material and the

texture Texture may refer to: Science and technology * Surface texture, the texture means smoothness, roughness, or bumpiness of the surface of an object * Texture (roads), road surface characteristics with waves shorter than road roughness * Texture ...

of the

road surface A road surface (British English), or pavement (American English), is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, hoggin, cob ...

on the traction produced by the wheels of a

vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), ...

. Road slipperiness can be measured either in terms of the friction between a freely-spinning wheel and the ground, or the

braking distance Braking distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. It is primarily affected by the original speed of the vehicle and the coefficient of friction b ...

of a braking vehicle, and is related to the

coefficient of friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

between the tyre and the road surface.

Public works Public works are a broad category of infrastructure projects, financed and constructed by the government, for recreational, employment, and health and safety uses in the greater community. They include public buildings ( municipal buildings, sc ...

agencies spend a sizeable portion of their budget measuring and reducing road slipperiness. Even a small increase in slipperiness of a section of road can increase the accident rate of the section of road tenfold. Maintenance activities affecting slipperiness include

drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic condition ...

repair,

snow removal Snow removal or snow clearing 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 and anti-icing De-icing is defined as removal ...

and

street sweeping A street sweeper or street cleaner may refer to a person's occupation or to a machine that cleans streets. Street sweepers have been employed in cities as "sanitation workers" since sanitation and waste removal became a priority. A str ...

. More intensive measures may include grinding or milling a surface that has worn smooth, a surface treatment such as a

chipseal Chipseal (also chip seal or chip and seal) is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of fine aggregate. In the United States, chipseals are typically used on rural roads carrying low ...

, or overlaying a new layer of asphalt. A specific road safety problem is

split friction Split friction (or μ (mu) - split) is a road condition that occurs when the friction significantly differs between the left and the right wheelpath. The road may then not be perceived as hazardous when accelerating, cruising or even braking soft ...

or μ (mu) - split; when the friction significantly differs between the left and the right wheelpath. The road may then not be perceived as hazardous when accelerating, cruising or even braking softly, but in a case of hard braking, the difference in friction will cause the vehicle to start to rotate towards the side offering higher grip. Split friction may cause jack-knifing of articulated trucks, while trucks with towed trailers may experience trailer swing phenomena. Split friction may be caused by an improper road spot repair that results in high variance of texture (roads) and colour (thin ice on newly paved black spots thaws faster than ice on old greyish asphalt) across the road section.

Measurement

The two ways to measure road slipperiness are surface friction testing and stopping distance testing. Friction testing can use surface friction testers o
portable friction testers
and involves allowing a freely moving object, usually a wheel, to move against the surface. By measuring the resistance experienced by the wheel, the friction between the ground and the wheel can be found. Stopping distance testing involves performing an

emergency stop A kill switch, also known as an emergency stop (E-stop), emergency off (EMO) and as an emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usual manner. Unlike a normal ...

in a test vehicle and measuring the distance required to come to a stop. This can be measured either from the length of the skid marks left by the vehicle, or by the "chalk-to-gun" method, where the brakes are connected to a small gun filled with chalk powder, which marks the point when the brakes were applied. This has the advantage of measuring the full stopping distance, while simply measuring the skid marks only measures the distance from the point where the wheels began to lock or slip. Measurement of skidding resistance is not yet universally harmononised despite a number of attempts such as

FEHRL FEHRL, the Forum of European National Highway Research Laboratories was created in 1989 as an international organisation. In 2000, it became an ''association international sans but lucratif'' (AiSBL) or International association without lucrative pu ...

's HERMES project. The European Standards Organisation ( CEN)has been working on the topic for many years through its committee CEN/TC 227 - Road materials. Contributions to this were made through the FP7 Tyrosafe project which aims to raise awareness, to coordinate and prepare for European harmonisation and to optimise the assessment and management of essential tyre/road interaction parameters in order to increase safety and support greening of road transport. This project will provide a synopsis of the current state of scientific understanding and its current application in different standards. It will identify the needs for future research and propose a way forward in the context of the future objectives of road administrations in order to optimise three key properties of roads: skid resistance,

rolling resistance Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy ...

and tyre/road noise emission.

Reduction

Road slipperiness can contribute to car accidents. In 1997, over 53,000 accidents were caused by slippery roads in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...

out of an estimated 4,000,000 accidents (or approximately 1.3 per cent) . A small change in road slipperiness can have a drastic effect on surface friction: decreasing the coefficient of friction from 0.45 to 0.35, equivalent to adding a dusting of wet snow, increased the accident rate by almost 1000%. As such, road agencies have a number of approaches to decreasing road slipperiness. Most roads are designed with a

convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytop ...

camber to provide sufficient

, thereby allowing surface water to drain out of the road. Trouble sections include entrances and exits of banked outercurves, where the

cross slope Cross slope, cross fall or camber is a geometric feature of pavement surfaces: the transverse slope with respect to the horizon. It is a very important safety factor. Cross slope is provided to provide a drainage gradient so that water will run ...

is close to zero. Unless these sections have a longitudinal grade of at least 0.4–0.5%, the drainage gradient (resultant to crossfall and longitudinal grade) will be lower than 0.5% so water will not run off the road surface.

Storm drain A storm drain, storm sewer (United Kingdom, U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surfa ...

s may be installed at regular intervals and modern paving materials are designed to provide high friction in most conditions.

Permeable paving Permeable paving surfaces are made of either a porous material that enables stormwater to flow through it or nonporous blocks spaced so that water can flow between the gaps. Permeable paving can also include a variety of surfacing techniques ...

allows water to soak through the paving material, reducing slipperiness in very adverse conditions. Road slipperiness can be prevented or delayed by proper pavement design. The

aggregate Aggregate or aggregates may refer to: Computing and mathematics * collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...

used in the pavement should be selected with care, as certain aggregates such as

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

may ''polish'', or wear smooth under the action of tires. With asphalt pavements and surface treatments, using too much asphalt or asphalt emulsion can cause

bleeding Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...

or ''flushing'', a condition where excess asphalt rises to the top and fills in the road texture. Both problems increase slipperiness, especially when the pavement is wet. Once lost, pavement texture can be restored with retexturing procedures such as diamond grinding of pavement, surface treatments such as

ing and resurfacing with

asphalt concrete Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parki ...

. Snow and ice removal also decreases road slipperiness;

snowplough A snowplow (also snow plow, snowplough or snow plough) is a device intended for mounting on a vehicle, used for removing snow and ice from outdoor surfaces, typically those serving transportation purposes. Although this term is often used to re ...

s and snow blowers can remove the snow from the road surface while

gritter A winter service vehicle (WSV), or snow removal vehicle, is a vehicle specially designed or adapted to clear thoroughfares of ice and snow. Winter service vehicles are usually based on a dump truck chassis, with adaptations allowing them to carr ...

s drop road salt and

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...

, which both melts the snow and ice from the road surface, and provide a rougher surface to grip onto. However, in dry conditions, sand and salt on the road surface can themselves increase road slipperiness and pose a danger to road traffic, and therefore, roads are cleared by street sweepers after

roadworks Roadworks (called road work or road construction in the United States) occur when part of the road, or in rare cases, the entire road, has to be occupied for work relating to the road, most often in the case of road surface repairs. In the ...

and gritting to make sure that all the loose material is cleared from the road surface.

References

{{Reflist "Volume 7" of the UK Design Manual for Roads and Bridges (DMRB), specifically HD 37/99: Section 5: Part 2: Chapter 11. TRL Report 298 : Mechanical retexturing of roads : A study of processes and early-life performance. TRL Report 299 : Mechanical retexturing of roads : An experiment to assess durability

External links

Defeating road ice
Road safety Snow removal Road hazards Articles containing video clips

Measurement

Reduction

See also

References

External links