Gravel road
Encyclopedia
Pavement (material)
Road surface or pavement 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 In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...
road
Road
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
surfaced with gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
that has been brought to the site from a quarry
Quarry
A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...
or stream bed
Stream bed
A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...
. They are common in less-developed nations, and also in the rural areas of developed nations such as Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. In New Zealand, they are known as 'metal roads'. They may be referred to as 'dirt roads' in common speech, but that term is used more for unimproved roads
Dirt road
Dirt road is a common term for an unpaved road made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable for vehicles; a narrower path for pedestrians, animals, and possibly small vehicles would be called a...
with no surface material added. If well constructed and maintained, a gravel road is an all-weather road.
The gravel used consists of irregular stones mixed with a varying amount of sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
, and clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
, which can act as a binder. A gravel road is quite different from a 'gravel drive', popular as private driveway
Driveway
A driveway is a type of private road for local access to one or a small group of structures, and is owned and maintained by an individual or group....
s in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. This uses clean gravel consisting of uniform, rounded stones and small pebble
Pebble
A pebble is a clast of rock with a particle size of 4 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered to be larger than granules and smaller than cobbles . A rock made predominantly of pebbles is termed a conglomerate...
s.
Construction
Compared to sealed roads, which require large machinery to work and pour concreteConcrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
or to lay and smooth a bitumen-based surface, gravel roads are easy and cheap to build. However, compared to dirt road
Dirt road
Dirt road is a common term for an unpaved road made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable for vehicles; a narrower path for pedestrians, animals, and possibly small vehicles would be called a...
s, all-weather gravel highways are quite expensive to build, as they require front loader
Loader (equipment)
A loader is a heavy equipment machine often used in construction, primarily used to load material into or onto another type of machinery .-Heavy equipment front loaders:A loader A loader is a heavy equipment machine often used in construction, primarily used to load material (such as asphalt,...
s, dump trucks, grader
Grader
A grader, also commonly referred to as a road grader, a blade, a maintainer, or a motor grader, is a construction machine with a long blade used to create a flat surface. Typical models have three axles, with the engine and cab situated above the rear axles at one end of the vehicle and a third...
s and roadrollers to provide a base course
Base course
Base Course in pavements refers to the sub-layer material of an asphalt roadway and is placed directly on top of the undisturbed soil so as to provide a foundation to support the top layer of the pavement...
of hard-packed earth or other material, sometimes macadam
Macadam
Macadam is a type of road construction pioneered by the Scotsman John Loudon McAdam in around 1820. The method simplified what had been considered state-of-the-art at that point...
ised, covered with one or more different layers of gravel. Graders are also used to produce a more extreme camber
Camber
Camber may refer to a variety of curvatures and angles:* Camber angle, the angle made by the wheels of a vehicle* Camber thrust in bike technology* In the steel industry, the concavity of rolls...
compared to a paved road to aid drainage, as well as construct drainage ditches and embankment
Embankment (transportation)
To keep a road or railway line straight or flat, and where the comparative cost or practicality of alternate solutions is prohibitive, the land over which the road or rail line will travel is built up to form an embankment. An embankment is therefore in some sense the opposite of a cutting, and...
s in low-lying areas. Cellular confinement
Cellular confinement
Cellular Confinement Systems are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention...
systems can be used to prevent the washboarding effect.
Laterite and murram roads
In AfricaAfrica
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and parts of Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, laterite
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
soils are used to build dirt roads. However laterite
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
, called murram in East Africa
East Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
, varies considerably in the proportion of stones (which are usually very small) to earth and sand. It ranges from a hard gravel to a softer earth embedded with small stones. Not all laterite and murram roads are therefore strictly gravel roads. Laterite and murram which contains a significant proportion of clay becomes very slippery when wet, and in the rainy season, it may be difficult even for four-wheel drive
Four-wheel drive
Four-wheel drive, 4WD, or 4×4 is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously...
vehicles to avoid slipping off very cambered roads into the drainage ditches at the side of the road. As it dries out, such laterite can become very hard, like sun-dried bricks.
Maintenance
Gravel roads require much more frequent maintenance than paved roads, especially after wet periods and when accommodating increased traffic. Wheel motion shoves material to the outside (as well as in-between travelled lanes), leading to rutting, reduced water-runoff, and eventual road destruction if unchecked. As long as the process is interrupted early enough, simple re-grading is sufficient, with material being pushed back into shape.Another problem with gravel roads is washboarding — the formation of corrugations
Washboarding
Washboarding is the name of the process which results in unmetalled roads developing a series of regular bumps with short spacing in the road surface...
across the surface at right angles to the direction of travel. They can become severe enough to cause vibration in vehicles so that bolts loosen or cracks form in components. Grading removes the corrugations, and reconstruction with careful choice of good quality gravel can help prevent them re-forming. Additionally, installing a cellular confinement system
Cellular confinement
Cellular Confinement Systems are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention...
will prevent the washboard-like corrugations from occurring.
Gravel roads are often found in cold climates because they are less vulnerable to freeze / thaw damage than asphalt
Asphalt concrete
Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...
roads and also because the inferior surface of gravel is not an issue if the road is covered by snow and ice for extended periods.
Driving
Although well-constructed and graded gravel roads are suitable for speeds of 100 km/h (60 mph), driving on them requires far more attention to variations of the surface and it is easier to lose control than on a paved road. In addition to potholes, ruts and loose stony or sandy ridges at the edges or in the middle of the road, problems associated with driving on gravel roads include:- sharper and larger stones cutting and puncturing tires, or being thrown up by the wheels and damaging the underside, especially puncturing the fuel tank of unmodified cars
- stones skipping up hitting the car body, lights or windshieldWindshieldThe windshield or windscreen of an aircraft, car, bus, motorbike or tram is the front window. Modern windshields are generally made of laminated safety glass, a type of treated glass, which consists of two curved sheets of glass with a plastic layer laminated between them for safety, and are glued...
s when two vehicles pass - dust thrown up from a passing vehicle reducing visibility
- 'washboard' corrugations cause loss of control or damage to vehicles
- skidding on mud after rain
- in higher rainfall areas, the increased camber required to drain water, and open drainage ditches at the sides of the road, often cause vehicles with a high centre of gravity, such as trucks and off-road vehicles, to overturn if they do not keep close to the crown of the road.
- Tire wear increases by 40%-50% on Gravel Roads
- Excess dust permeates door-opening rubber moulding breaking the seal
- Lost binder in the form of road dust, when mixed with rain, will wear away the painted surfaces of vehicles
Forest service road
Forest Service
Forest Service may refer to:* Canadian Forest Service* Indian Forest Service* New Zealand Forest Service* United States Forest Service* Forestry Commission in the United Kingdom...
to access remote undeveloped areas. These roads are built mainly for the purposes of the logging industry
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
and forest management workers, although in some cases they are also used for backcountry
Backcountry
A backcountry area in general terms is a geographical region that is:* isolated* remote* undeveloped* difficult to accessThe term may apply to various regions that are reasonably close to urban areas but are:* not immediately accessible by car...
recreation access.
Networks of tributary roads branch off from a trunk
Trunk road
A trunk road, trunk highway, or strategic road is a major road—usually connecting two or more cities, ports, airports, and other things.—which is the recommended route for long-distance and freight traffic...
FSR. Roads are usually named after a regional district, and branches have an alphanumeric
Alphanumeric
Alphanumeric is a combination of alphabetic and numeric characters, and is used to describe the collection of Latin letters and Arabic digits or a text constructed from this collection. There are either 36 or 62 alphanumeric characters. The alphanumeric character set consists of the numbers 0 to...
designation.
Typically, a high-clearance four-wheel drive vehicle is required to travel effectively on a road, especially where large pothole
Pothole
A pothole is a type of disruption in the surface of a roadway where a portion of the road material has broken away, leaving a hole.- Formation :...
s and/or waterbar
Waterbar
A water bar or interceptor dyke is a road construction feature that is used to prevent erosion on sloping roads, cleared paths through woodland , or other accessways by reducing flow length...
s are present. Switchback
Hairpin turn
A hairpin turn , named for its resemblance to a hairpin/bobby pin, is a bend in a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn almost 180° to continue on the road. Such turns in ramps and trails may be called switchbacks in American English, by analogy...
s are employed to make the road passable through steep terrain.
These roads rapidly fall into disrepair and quickly become impassable. Remnants of old roads can exist for decades. They are eventually erased by washout, erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
, and ecological succession
Ecological succession
Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...
.
Logging roads
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
and other forest management operations. They are commonly narrow, winding, and unpaved, but main haul roads can be widened, straightened or paved if traffic volume warrants it.
The choice of road design standards is a trade off between construction costs and haul costs (which the road is designed to reduce). A road that serves only a few stands will be used by relatively few trucks over its lifetime, so it makes sense to save construction costs with a narrow, winding, unpaved road that adds to the time (and haul costs) of these few trips. A main haul road serving a large area however will be used by many trucks each day, and each trip will be shorter (saving time and money) if the road is straighter and wider, with a smoother surface.
Logging trucks are generally given right of way. In areas where this practice is regulated (or is supposed to be) non-highway roads with heavy logging traffic may be "radio-controlled", which is to say a CB radio
Citizens' band radio
Citizens' Band radio is, in many countries, a system of short-distance radio communications between individuals on a selection of 40 channels within the 27-MHz band. Citizens' Band is distinct from the FRS, GMRS, MURS and amateur radio...
on board any vehicle on the road is advised for safety reasons.
See also
- Dirt roadDirt roadDirt road is a common term for an unpaved road made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable for vehicles; a narrower path for pedestrians, animals, and possibly small vehicles would be called a...
- ErosionErosionErosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
- Forest HighwayForest HighwayForest Highways or Forest Routes are a category of roads within United States National Forests. They are built to connect the national forests to the existing state highway systems, and to provide improved access to recreational and logging areas....
(US system of maintained forest roads) - LoggingLoggingLogging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
- Roads
- TrailTrailA trail is a path with a rough beaten or dirt/stone surface used for travel. Trails may be for use only by walkers and in some places are the main access route to remote settlements...