Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems (2012)

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119 Acceptance Testing—Crash tests reported to FHWA to obtain a letter accepting a roadside hardware item to be considered acceptable for use on the National Highway System. Anchor—a mass designed to counter the tension forces in a cable barrier system at either end. These are usually large concrete blocks whose size and depth are a function of the soil conditions. Anchor Spacing—The distance between end anchors for a continuous length of cable barrier. Anchorage—See Anchor. Asymmetric Cross-Section—A median cross-section that has unequal side slopes. Barrier Interface Envelope—A graph or plot that depicts variations in vehicle vertical position as it traverses the median at different speeds and angles. In some cases, more than one vehicle type is incorporated in the envelope. Barrier Transition—The device or hardware used to link one type of barrier to another in a fashion that will function safely. Cable Barrier Technology—Various designs for cable barrier systems. Cable Tension—The amount of tensile force in the cable. Cable Post—A semi-rigid steel beam of varying shape used to provide support for cables before and during an impact. Cable Connector—A device (e.g., hook bolt, hair pin, or similar fixture) designed to hold the cable at a specific height. Cable Splices—Connection between cable sections that are physically joined to provide the needed continuity. CarSim—Commercially available software for vehicle dynamics analysis distributed by Mechanical Simulation Corporation. Central Reserve—Common international term for median. See Median. Crash Simulation—A computer process that predicts the vehicle and/or barrier response of a crash event. Cross Median Crash—A crash between two or more vehicles that follows a vehicle crossing over the median from the opposite side of the highway. Cross-Median Event—An event where a vehicle wholly or partially crosses the median. These may or may not result in a crash. Crossovers—Points along a divided highway where vehicles can transfer to travel in the opposite direction. Usually restricted to emergency or maintenance vehicles. Deflection—The amount of lateral displacement of a barrier from its original position to that during or after an impact. Durability—The ability of a material or device to function effectively over time. Finite Element Models—Representations of objects created by subdividing the entire item into small pieces for which their geometry, material characteristics, contacts, and failure modes are defined. In time-based simulations, each element is subjected to forces that cause movement, Glossary

120 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems deformation, or failures. Systematic updates of the changes to each element allow replication of impacts or other physical changes. Furrowing—The sinking into the median soil when wet or very dry causing the vehicle’s interface area to be lower at point of impact. Guidelines—A structured set of guidance statements reflecting a consensus. Guidance—Statements that provide soundly based directives for undertaking an action. GWU—George Washington University. High-Tension—A cable barrier system that has higher initial tension and stronger post-to-cable connection than the original generic cable barrier systems. The high-tension systems experience lower deflection during impacts than the original systems but may require larger anchors. HVE (Human Vehicle Environment)—Software tool for vehicle dynamics analysis distributed by Engineering Dynamics Corporation. Interface Trace Plot—A diagram showing the relative position of points defining the interface region of the front of a vehicle as it traverses a specific path as viewed from a downstream point perpendicular to the centerline of the road. Interface Region—The front area of a vehicle that has sufficient structural integrity to interact with a barrier. This varies by vehicle. Interface Envelope—The area subtended by the points defining the primary structural region on the front of the vehicle as it traverses a specific path as viewed from a downstream point perpendicular to the centerline of the road. Lower Trace Limit—See Underride Limit. Low-Tension—A term used to define the original generic cable barrier system in which the tension in the cables is about 4,450 N (1,000 lb) at 18°C (65°F). LS-DYNA—Finite element simulation software developed by the Livermore Software & Tech- nology Corporation. Maintenance Cycles—Repetitive actions in time to keep a device functional. MASH—Manual for Assessment of Safety Hardware. AASHTO hardware crashworthiness testing protocols and standards. Maximum Lower Cable Height—The highest a bottom cable can be to allow engagement between the vehicle and barrier to avoid underride for the selected vehicle or set of vehicles. Median—An unpaved area between opposing lanes of traffic and associated shoulders. Median Configuration—The features of the median cross-section. Median Cross-Section—The dimensions, slopes, and shape that result from passing a plane perpendicular to the road at any given point. Median Profiles—The features of the median cross-section. Median Shape—See median profiles. Median, Asymmetrical—A cross-section with unequal side slopes that converge to a central point. Median, Flat Bottom—A cross-section with equal side slopes that extend to a flat-bottomed area of a given depth. Median, Multi-Slope/Broken Back—A cross-section with two or more side slopes that converge to a central point. Median, Raised—Medians have up-slopes from the edge of the shoulder. Median, Rounded Bottom—A cross-section with equal side slopes that converge to a central point that has a rounded transition from one side to the next. Median, V-Shaped—A cross-section with equal side slopes that converge to a central point. Minimum Upper Cable Height—The lowest a top cable can be to allow engagement between the vehicle and barrier to avoid override for the selected vehicle or set of vehicles. Mow Strips—A paved area along the cable line that eliminates the need for grass mowing around the posts. MwRSF—Midwest Roadside Safety Facility at University of Nebraska-Lincoln.

Glossary 121 NCAC—National Crash Analysis Center at George Washington University. NCHRP Report 350—Report 350 was adopted as the national standard for roadside hardware crashworthiness testing. Normalized Trace Plot—A trace plot or interface trace plot in which the vertical height of the reference points above the ground line (or surface) is plotted on a horizontal axis. Nuisance Hit—A random impact of a cable barrier that results in minor damage but often goes unreported because the vehicle recovers and is able to continue. May also occur from impacts associated with maintenance operations. Off-Tracking—The path of a vehicle that involves some degree of lateral sliding. Override—An event where all or part of a vehicle gets over the top of a barrier. Override Limit—A line (curve) defining the minimum height of the top cable that allows engagement between the vehicle and barrier to avoid overrides. The line defines the minimum height at different lateral placements of the barrier. Ploughing—See Furrowing. Prestretched Cable—Cable that is statically loaded after manufacture to reduce the slack in individual strands of the cable before installation. Primary Structural Region—See Interface region. Position Isobars—A continuous line that indicates the relative position of the cables for any lateral position across the median. Post Embedment—The method used to place a post to support the cables including direct driven, placed in a socket, or installation in a drilled footing with compacted material or concrete. Retensioning—The mechanical process of increasing the tension in existing cables. Retrofit—Changing the configuration of the cable barrier design after initial deployment. Roadside—The area beyond the shoulder adjacent to the highway. RDG—AASHTO Roadside Design Guide. Sleeve—A type of footing that allows a post to be readily inserted or removed after installation. Slope Rounding—The process of regarding sloped medians such that the edges at the breakpoint are curved with a certain radius. Socket—A concrete foundation for posts that allows them to slide in or out. Sockets greatly facilitate rapid repair of damaged cable barrier posts after an impact. Socketed Posts—See Socket. Spring Response—The incremental dampening of forces by a spring directed toward restoring equilibrium. Strand—A single wire in the bunch of twisted wires that constitutes the cable or wire rope com- ponent. Sometimes used to refer to the bunch of cables (e.g., three-strand, low-tension system). Safety Fence—Common international term for guardrail or cable barrier system. Trace Plot—The diagram showing the relative position of a point on a vehicle as it traverses a specific path as viewed from a downstream point perpendicular to the centerline of the road. Tracking—See Off-Tracking. Tension Compensators—A device that incorporates springs to regulate the tension in the cables. These devices are used in generic, low-tension cable barriers. Tolerances—The permissible range of variation in construction and installation of cable barriers (these could be dimensions, mechanical properties, measurements, etc.). Transitions—See Interconnections. TTI—Texas Transportation Institute at Texas A&M University. Underride—An event where all or part of a vehicle goes under the lowest longitudinal element of a barrier. Underride Limit—A line (curve) defining the maximum height of the bottom cable that allows engagement between the vehicle and barrier and avoids underrides. The line defines the maximum height at different lateral placements of the barrier. Upper Trace Limit—see Override Limit.

122 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems Validation—The process of determining how well a model represents the real situation. Vaulting—See Override. Vehicle Dynamics—The physics of the forces acting on a vehicle as it moves across a surface considering the features of the vehicle. Vehicle Dynamics Analysis (VDA)—The analysis of the physics of a moving vehicle with specific design characteristics (e.g., mass, suspension features, length) that is influenced by the loaded mass, speed, and direction of the vehicle and surface conditions (e.g., slope, surface firmness, friction) of the vehicle’s path. Vehicle Trajectory—the path a vehicle takes as it traverses across roadway and roadside features. Verge—International term for shoulder or gore area at on- or off-ramps of highways. Wire Rope Safety Fence—International term for cable barrier. See Cable Barrier.