Profilograph
Encyclopedia
The profilograph is a device used to measure pavement surface roughness. In the early 20th century, Profilographs were low speed rolling devices. Today many Profilographs are advanced high speed systems with a laserbased height sensor in combination with a inertial system that creates a large scale reference plane. It is used by construction crews or certified consultants to measure the roughness of in-service road networks, as well as before and after milling off ridges and paving
overlays. Modern profilographs are fully computerized instruments.
The data collected by a profilograph is used to calculate the International Roughness Index
(IRI), which is expressed in units of inches/mile or mm/m. IRI values range from 0 (equivalent to driving on a plate of glass) upwards to several hundred in/mile (a very rough road). The IRI value is used for road management to monitor road safety and quality issues.
Many road profilographs are also measuring the pavements cross slope
, curvature
, longitudinal gradient
and rutting. Some profilographs take digital photos or video
s while profiling the road. Most profilographs also record the position, using GPS technology. Yet another common measurement option is cracks
. Some profilograph systems include a ground penetrating radar, used to record asphalt
layer thickness.
Another type of profilograph system is for measuring the surface texture (roads)
of a road and how it relates to the coefficient of friction
and thus to skid resistance. Pavement texture is divided into three categories; megatexture (roads)
, macrotexture
, and microtexture
. Microtexture cannot currently be measured directly, except in a laboratory. Megatexture is measured using a similar profiling method as when obtaining IRI values, while macrotexture is the measurement of the individual variations of the road within a small interval of a few centimeters. For example, a road which has gravel spread on top followed by an asphalt seal coat will have a high macrotexture, and a road built with concrete slabs will have low macrotexture. For this reason, concrete is often grooved or roughed up immediately after it is laid on the road bed to increase the friction between the tire and road.
Equipment to measure macrotexure currently consists of a distance measuring laser with an extremely small spot size (< 1 mm) and data acquisition systems capable of recording elevations spaced at a mm or less apart. The sample rate is generally over 32 kHz. Macrotexture data can be used to calculate the speed-depending part of the friction number between typical car tires and the road surface. The macrotexture also give information on the difference between dry and wet road friciton. However, macrotexture cannot be used to calculate a relevant friction number, since also microtexture affects the friction.
Lateral friction and cross slope are the key reaction forces acting to keep a cornering vehicle in steady lateral position, while exposed to exciting forces from speed and curvature. Since friction is strongly dependant on macrotexture, and texture, cross slope as well as curvature can be measured with a road profilographs, road profilographs are very useful to identify improperly banked curves (see banked turn
) that are posing a great risk to motor vehicle accidents.
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...
overlays. Modern profilographs are fully computerized instruments.
The data collected by a profilograph is used to calculate the International Roughness Index
International Roughness Index
The International Roughness Index is the roughness index most commonly obtained from measured longitudinal road profiles. It is calculated using a quarter-car vehicle math model, whose response is accumulated to yield a roughness index with units of slope...
(IRI), which is expressed in units of inches/mile or mm/m. IRI values range from 0 (equivalent to driving on a plate of glass) upwards to several hundred in/mile (a very rough road). The IRI value is used for road management to monitor road safety and quality issues.
Many road profilographs are also measuring the pavements cross slope
Cross slope
Cross slope is a geometric feature of pavement surfaces; the transversal slope [%] with respect to the horizon. It is a very important safety factor. One task is to make water run off the surface to a drainage system, as Cross Slope is the main contributor to Pavement Drainage gradient. Very low...
, curvature
Curvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...
, longitudinal gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
and rutting. Some profilographs take digital photos or video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
s while profiling the road. Most profilographs also record the position, using GPS technology. Yet another common measurement option is cracks
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
. Some profilograph systems include a ground penetrating radar, used to record asphalt
Asphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...
layer thickness.
Another type of profilograph system is for measuring the surface texture (roads)
Texture (roads)
Road surface texture are deviations from a planar surface, affecting the vehicle/tyre interaction. Pavement texture is divided into:* Microtexture with wavelengths from 0 mm up to 0.5 mm* Macrotexture with wavelengths from 0.5 mm up to 50 mm...
of a road and how it relates to the coefficient of friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
and thus to skid resistance. Pavement texture is divided into three categories; megatexture (roads)
Megatexture (roads)
Megatexture is a family of wave-shaped road surface characteristics. While vehicle suspension deflection and dynamic tyre loads are affected by longer waves , road texture affects the interaction between the road surface and the tyre footprint. Megatexture has wavelengths from 50 mm up to 500 mm...
, macrotexture
Macrotexture
Macrotexture is a family of wave-shaped road surface characteristics. While vehicle suspension deflection and dynamic tyre loads are affected by longer waves , road texture affects the interaction between the road surface and the tyre footprint. Macrotexture has wavelengths from 0.5 mm up to...
, and microtexture
Microtexture
Microtexture is the collative term for a material's crystallographic parameters and other aspects of microstructure: such as morphology, including size and shape distributions; chemical composition; and crystal orientation and relationships...
. Microtexture cannot currently be measured directly, except in a laboratory. Megatexture is measured using a similar profiling method as when obtaining IRI values, while macrotexture is the measurement of the individual variations of the road within a small interval of a few centimeters. For example, a road which has gravel spread on top followed by an asphalt seal coat will have a high macrotexture, and a road built with concrete slabs will have low macrotexture. For this reason, concrete is often grooved or roughed up immediately after it is laid on the road bed to increase the friction between the tire and road.
Equipment to measure macrotexure currently consists of a distance measuring laser with an extremely small spot size (< 1 mm) and data acquisition systems capable of recording elevations spaced at a mm or less apart. The sample rate is generally over 32 kHz. Macrotexture data can be used to calculate the speed-depending part of the friction number between typical car tires and the road surface. The macrotexture also give information on the difference between dry and wet road friciton. However, macrotexture cannot be used to calculate a relevant friction number, since also microtexture affects the friction.
Lateral friction and cross slope are the key reaction forces acting to keep a cornering vehicle in steady lateral position, while exposed to exciting forces from speed and curvature. Since friction is strongly dependant on macrotexture, and texture, cross slope as well as curvature can be measured with a road profilographs, road profilographs are very useful to identify improperly banked curves (see banked turn
Banked turn
A banked turn is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. The bank angle is the angle at which the vehicle is inclined about its longitudinal axis with respect to its path....
) that are posing a great risk to motor vehicle accidents.
See also
- RoadRoadA 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...
- Roughness
- Rut (roads)Rut (roads)A rut is a depression or groove worn into a road or path by the travel of wheels or skis. Ruts can be formed by wear, as from studded snow tires common in cold climate areas, or they can form through the deformation of the asphalt concrete pavement or subbase material...
- Superelevation
- Texture (roads)Texture (roads)Road surface texture are deviations from a planar surface, affecting the vehicle/tyre interaction. Pavement texture is divided into:* Microtexture with wavelengths from 0 mm up to 0.5 mm* Macrotexture with wavelengths from 0.5 mm up to 50 mm...
- ProfilometerProfilometerProfilometer is a measuring instrument used to measure a surface's profile, in order to quantify its roughness.While the historical notion of a profilometer was a device similar to a phonograph that measures a surface as the surface is moved relative to the contact profilometer's stylus, this...
- Ride qualityRide qualityRide quality refers to the degree of protection offered vehicle occupants from uneven elements in the road surface, or the terrain if driving off-road. A car with very good ride quality is also a comfortable car to ride in. Cars which disturb vehicle occupants with major or minor road...