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FHWA Home / Safety / Roadway Departure / Low-Cost Treatments for Horizontal Curve Safety 2016

Low-Cost Treatments for Horizontal Curve Safety 2016


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Term Description
Acrylic material

Binder material used in high friction surface treatment that holds the aggregate firmly to the pavement.

ADT Average Daily Traffic – the traffic volume of a road measured in vehicles per day.
Advisory speed plaque A sign that is placed below a Horizontal Alignment sign to advise motorists of the safe speed through the curve.
Ball bank indicator An inclinometer that is used for determining safe curve speeds for horizontal curves.
Cable barrier

A flexible barrier made from wire rope supported between frangible posts.

Calcined bauxite aggregate A hard, coarse aggregate used in high friction surface treatment.
Clear Zone The unobstructed traversable area provided beyond the edge of the through traveled way for the recovery of errant vehicles, as defined by AASHTO.
CMF Crash Modification Factor – a multiplicative factor used to compute the expected number of crashes after implementing a countermeasure.
CMF Clearinghouse

A website that provides the largest collection of CMFs for geometric design elements and traffic control devices available in the United States.

Compound curves Two or more tangential, consecutive curves.
Curve Deliniation Treatments that enhance the conspicuity of a curve (e.g., wider edge line, higher retroreflectivity of signs, postmounted delineators, chevrons, raised pavement markings).
Concrete safety shape

A rigid barrier that does not deflect.


A device mounted above the roadway surface and along the side of the road in a series to indicate roadway alignment.

Epoxy material

Binder material used in the application of high friction surface treatment that hold the aggregate firmly to the pavement.

FARS Fatality Analysis Reporting System – a nationwide census providing annual data regarding fatal injuries in motor vehicle traffic crashes.
Guardrail A semi-rigid barrier usually either a steel box beam or W-beam that deflect less than flexible barriers.
HFST High Friction Surface Treatment – a thin layer of aggregate bonded to the pavement surface designed to increase friction and compensate for sharp curves.
Milled Milled rumble strips are made by a machine with a rotary cutting head, creating a smooth, uniform, and consistent groove in the pavement. They cause tire noise and vehicle vibration when traversed.
MUTCD Manual on Uniform Traffic Control Devices – defines the standards used by road managers nationwide to install and maintain traffic control devices on all public streets, highways, bikeways, and private roads open to public traffic.
Pavement grooving A pavement countermeasure technique to apply longitudinal or transverse cuts onto the pavement surface to increase or restore pavement friction.
Pavement raveling Deterioration of the pavement surface caused by aggregate particles becoming dislodged.
Retroreflective A material or device that reflects light back to its source.
RSA Road Safety Audit – a formal safety performance examination of an existing or future road or intersection by an independent, multidisciplinary team.
Safety EdgeSM A paving technique used system-wide to improve pavement durability and reduce crashes by shaping and consolidating the pavement edge into a 30 degree wedge.
Superelevation The banking of a horizontal curve.
Systemic approach The analysis of crash data on a system-wide basis that considers identifying factors that indicate higher risks for severe crashes.


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Page last modified on February 16, 2017
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