A surface friction tester, used to measure road slipperiness
Road slipperiness is a condition of low skid resistance due to insufficient road friction. It is a result of snow, ice, water, loose material and the texture of the road surface on the traction produced by the wheels of a vehicle.[1]
Road slipperiness can be measured either in terms of the friction between a freely-spinning wheel and the ground, or the braking distance of a braking vehicle, and is related to the coefficient of friction between the tyre and the road surface.
Public works 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.[2] Maintenance activities affecting slipperiness include drainage repair, snow removal and street sweeping. More intensive measures may include grinding or milling a surface that has worn smooth, a surface treatment such as a chipseal, or overlaying a new layer of asphalt.
A specific road safety problem is split friction 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.
^Dillard, Jack; Mahone, David (1964). "Measuring Road Surface Slipperiness". ASTM Special Technical Publication.
^Wallman, Carl Gustav (2001). "Friction measurement methods and the correlation between road friction and traffic safety" (PDF).[permanent dead link]
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