Road slipperiness is a condition of low skid resistance due to insufficient road friction. It is a result of

snow Snow consists of 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 througho ...

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

, loose material and the

texture Texture may refer to: Science and technology * Image texture, the spatial arrangement of color or intensities in an image * Surface texture, the smoothness, roughness, or bumpiness of the surface of an object * Texture (roads), road surface c ...

of the

road surface A road surface (British English) or pavement (North 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, macadam, ...

on the traction produced by the wheels of a

vehicle A vehicle () is a machine designed for self-propulsion, usually to transport people, cargo, or both. The term "vehicle" typically refers to land vehicles such as human-powered land vehicle, human-powered vehicles (e.g. bicycles, tricycles, velo ...

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

braking distance A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

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. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

between the tyre and the road surface.

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

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 water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root gro ...

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 both by individual households and by governments institutions, and commercial businesses. De-icing and anti-icing De-icin ...

and street sweeping. 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 or spray seal) is a pavement surface treatment that combines one or more layers of asphalt with one or more layers of fine aggregate. In the United States, chipseals are typically used on rural roads c ...

, 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 so ...

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) Road surface textures are deviations from a planar and smooth surface, affecting the vehicle/tyre interaction. Pavement texture is divided into: microtexture with wavelengths from 0 mm to , macrotexture with wavelengths from to and megate ...

and colour (thin ice on newly paved black spots thaws faster than ice on old greyish asphalt) across the road section.

Measurement

Anchorage Police recruits participating in Emergency Vehicle Operations Course at Joint Base Elmendorf-Richardson

The two ways to measure road slipperiness are surface friction testing and stopping distance testing. Friction testing can use surface friction testers or 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 more formally as an emergency brake, emergency stop (E-stop), emergency off (EMO), or emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usu ...

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'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 (physics), motion when a body (such as a ball, tire, or wheel) Rolling, rolls on a surface. It is mainly caused by Plasticity (physics), non- ...

and tyre/road noise emission.

Reduction

Road slipperiness can contribute to

car accident A traffic collision, also known as a motor vehicle collision, or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other moving or stationary obstruction, such as a tree, pole or building. T ...

s. 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 Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

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 of ...

is close to zero. Unless these sections have a longitudinal grade of at least 0.4–0.5%, the

drainage gradient Drainage gradient (DG) is a term in road design, defined as the combined slope due to road surface cross slope (CS) and longitudinal slope (hilliness). Although the term may not be used, the concept is also used in roof design and landscape arc ...

(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), highway drain, surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from i ...

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 fo ...

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

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 Diamond grinding is a pavement preservation technique that corrects a variety of surface imperfections on both concrete and asphalt concrete pavements. Most often utilized on concrete pavement, diamond grinding is typically performed in conjunctio ...

, surface treatments such as

ing and resurfacing with

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

. Snow and ice removal also decreases road slipperiness; snowploughs and

snow blower A snow blower or snowblower or snow thrower is a machine for removing snow from an area where it is problematic, such as a driveway, sidewalk, roadway, railroad track, ice rink, or runway. The commonly used term "snow blower" is a misnomer, a ...

s can remove the snow from the road surface while gritters drop

road salt Road salt (also known as de-icing salt, rock salt, or snow 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. Various kinds of salts are used as road salt, but calciu ...

and

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

, 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, also called road construction or road work, 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 United States road ...

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