Texture (roads)

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Road surface textures are deviations from a planar surface, affecting the vehicle/tyre interaction. Pavement texture is divided into: Microtexture with wavelengths from 0 mm to 0.5 millimetres (0.020 in), Macrotexture with wavelengths from 0.5 millimetres (0.020 in) to 50 millimetres (2.0 in) and Megatexture with wavelengths from 50 millimetres (2.0 in) to 500 millimetres (20 in).

Microtexture[edit]

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[1]

While vehicle suspension deflection and dynamic tyre loads are affected by longer wavelength (roughness), road texture affects the interaction between the road surface and the tyre footprint. Microtexture has wavelengths shorter than 0.5 mm. It relates to the surface of the binder, of the aggregate, and of contaminations such as rubber deposits from tires.

MiTx contributes to dry road surface friction.

Typically, road agencies do not monitor MiTx directly, but indirectly by brake friction tests. However, friction also depends on other surface properties, such as Macrotexture.

Macrotexture[edit]

Macrotexture (MaTx) is partly a desired property and partly an undesired property. Short MaTx waves, about 5 mm, acts as acoustical pores and reduce tyre/road noise. On the other hand, long wave MaTx increase noise. MaTx provide wet road friction, especially at high speeds. Excessive MaTx increase rolling resistance and thus fuel consumption and CO2 emission contributing to global warming. Proper roads have MaTx of about 1 mm Mean Profile Depth.

Macrotexture (MaTx) is a family of wave-shaped road surface characteristics. While vehicle suspension deflection and dynamic tyre loads are affected by longer waves (roughness), road texture affects the interaction between the road surface and the tyre footprint. Macrotexture has wavelengths from 0.5 mm up to 50 mm. Other types of road texture are microtexture and megatexture.

Road agencies monitor macrotexture using measurements taken with highway speed laser or inertial profilometers.

Megatexture[edit]

Megatexture (MeTx) is the result of pavement wear and distress, causing noise and vibration. MeTx below 0.2 mm Root-Mean-Square is considered normal on proper roads.

Measurement[edit]

MaTx and MeTx are measured with laser/inertial Profilographs. Since MiTx has so short waves, it is preferably measured by dry friction brake tests rather than by profiling. Profilographs that record texture in both left and right wheel paths can be used to identify road sections with hazardous Split friction.

References[edit]

  1. ^ Microtexture Determination and its Applications (Second edition), V Randle, 2003