In-Service Performance Evaluation of Guardrail End Treatments (2018)

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Appendix B Glossary and Illustrations of Guardrail End Treatments and Other Roadside Safety Devices Presented below are definitions of terms related to guardrail end treatments and other roadside safety devices and illustrations of device types and crash test conditions, as follows: • Glossary of terms relating to the design and performance of guard- rail end treatments, excerpted from the glossary of the 2015 safety analysis report of the American Association of State Highway and Transportation Officials–Federal Highway Administration Task Force on guardrail end treatments (Joint AASHTO-FHWA Task Force on Guardrail Terminal Crash Analysis 2015) (see Box B-1). • Photographs of selected types of guardrail end treatments, includ- ing types referred to in the committee’s report (see Figure B-1). • Glossary of terms relating to the testing of roadside safety devices, excerpted from the glossary of National Cooperative Highway Research Program Report 350 on the crash testing of roadside safety devices (Ross et al. 1993) (see Box B-2). These definitions are consistent with those in the Manual for Assessing Safety Hardware (AASHTO 2009). • Illustration of the uses of roadside safety devices that are subject to crash testing (see Figure B-2). • Diagram of the configuration of the vehicle and end treatment in a crash test of a guardrail end treatment. Crash testing guidelines specify the vehicle characteristics, vehicle speed, angle and point of impact with the device, and evaluation criteria (see Figure B-3). 122

APPENDIX B 123 Box B-1 Definitions of Terms Relating to the Design and Performance of Guardrail End Treatments anchor The mechanism that fixes the ends of a run of guardrail to the ground, thus providing rail tension in the event of [an] impact. clear zone, clear roadside Flat, traversable terrain next to the traveled way that is available for an errant vehicle to slow, stop, or return to the roadway without encountering roadside hazards. crashworthy Refers to a roadside safety device that has passed the appropriate crash tests, typically in accordance with NCHRP Report 350 or the AASHTO Manual for Assessing Safety Hardware. energy-absorbing terminal A category of guardrail terminals that is designed to slow or stop an impacting vehicle through the use of energy dissipating mechanisms such as bending, kinking, crushing, or otherwise deforming the W-beam rail. extruding terminal, extruding guardrail terminal A specific type of energy absorbing guardrail terminal where the extruder head is designed to be pushed down the W-beam rail when impacted head-on, deforming the rail and directing it away from the vehicle. gate, gating The ability of a guardrail terminal to yield and bend out of the way when impacted at an angle, allowing an errant vehicle to proceed behind the rail. Most guardrail terminals, including all extruding terminals, gate when a vehicle impacts at an angle in the vicinity of the first three posts. guardrail, W-beam guardrail A semi-rigid post-and-steel-beam barrier designed to smoothly redirect a vehicle impacting the face of the barrier at some angle. A guardrail absorbs the energy of a crash through deformation and deflection of the W-beam rail, deformation of the guardrail posts, and rotation of the posts through the soil. guardrail end The leading or trailing limit of W-beam guardrail. guardrail face, guardrail run The length-of-need portion of a guardrail installation.

124 PERFORMANCE EVALUATION OF GUARDRAIL END TREATMENTS guardrail terminal, guardrail end terminal, guardrail end treatment, crash- worthy terminal, and terminal A device designed to anchor the leading end of a W-beam guardrail while reducing the likelihood of spearing, vaulting, or rolling a vehicle during head-on or angled impacts. head, extruder head, impact head The portion of an extruding terminal that rests on the end of the W-beam rail. The head deforms the W-beam as it is pushed down the rail by the vehicle. head-on impact Frontal impact into a guardrail terminal where the travel direction of the vehicle is in-line with or parallel to the run of guardrail. This impact is also referred to as a zero-degree impact. high-energy impact A crash involving a vehicle that exceeds the 4,400-pound mass of the ¾-ton pickup truck specified for crash testing of guardrail ter- minals and/or a crash where the impact speed was greater than 62 mph. (These conditions are beyond the NCHRP Report 350 Test Level 3 impact conditions.) length of need The middle portion of a guardrail installation, located away from the ends, or the length of guardrail needed in advance of a roadside feature to adequately shield it for a theoretical vehicle leaving the road along a cal- culated or presumed path. nontracking A vehicle skidding or sliding in a direction other than where its axis is pointing. This type of crash can result in a side impact or rollover. performance limitations Performance limitations are factors in a real-world crash environment that can contribute to the unsuccessful performance of a roadside safety hardware device. Crashworthy guardrail terminals and other safety hardware performance may be affected when in-service crashes are outside the limits of the ideal crash tested conditions. The performance of these devices is dictated by physical laws, vehicle stability, vehicle crashwor- thiness, and the site conditions of these real-world crashes. rolling, rollover Crash scenario where an errant vehicle rolls onto its side during a crash event. It may continue to roll onto its roof and stop, or roll multiple times. shallow-angle impact Frontal impact into a guardrail terminal where the travel direction of the vehicle is nearly parallel (approximately 10 degrees or less) to the run of guardrail. side impact Crash where the initial point of vehicle contact is the passenger side or driver side rather than the front or rear plane of the vehicle. Side impacts are typically nontracking events where the vehicle may be sliding at an angle or yawing. spearing Guardrail penetrating the exterior of an impacting vehicle and poten- tially penetrating into the occupant compartment. tracking A vehicle traveling in the same direction as its wheels are pointing. A tracking vehicle is not sliding or skidding sideways. vaulting Launching of a vehicle into the air upon impact with a roadside feature. SOURCE: Excerpted from Safety Analysis of Extruding W-Beam Guardrail Terminal Crashes. Joint AASHTO-FHWA Task Force on Guardrail Terminal Crash Analysis, 2015, pp. 121–124. https://www.fhwa.dot.gov/guardrailsafety/safetyanalysis. Box B-1 Continued

APPENDIX B 125 (a) (b) (c) (d) (e) (f) FIGURE B-1 Examples of guardrail end treatment types (FHWA 2015): (a) Slotted Rail Terminal (SRT-350), Trinity Highway, LLC (non–energy absorbing); (b) Flared Energy-Absorbing Terminal (FLEAT), Road Systems, Inc. (energy absorbing); (c) Sequential Kinking Terminal (SKT), Road Systems, Inc. (energy absorbing); (d) Ex- truder Terminal (ET-Plus), Trinity Highway, LLC (energy absorbing); (e) X-Tension Guardrail End Terminal, Barrier Systems, Inc. (energy absorbing); and (f) Bursting Energy Absorbing Terminal (BEAT), Road Systems, Inc. (energy absorbing).

126 PERFORMANCE EVALUATION OF GUARDRAIL END TREATMENTS Box B-2 Definitions of Terms Relating to Crash Testing of Roadside Devices crash cushion A device designed primarily to safely stop a vehicle within a rela- tively short distance. A redirective crash cushion is designed to contain and redirect a vehicle impacting downstream from the nose of the cushion. A nonredirective crash cushion is designed to contain and capture a vehicle impacting downstream from the nose of the cushion. crash test A test in which a production model test vehicle or a surrogate test vehicle impacts or traverses a highway feature. device Refers to a design or a specific part thereof, such as a breakaway device. Note that the terms “device” and “feature” are often synonymous. evaluation criteria Criteria used to assess the results of a crash test or to assess the in-service performance of a feature. feature Refers to a specific element of a highway. It may be a hardware item and its associated foundation, such as a sign or barrier installation, or it may be a geometric element, such as a side slope or a ditch cross-section. geometric feature A roadside cross-section element such as a ditch section, an embankment, a driveway or a median crossover, or a curb. It also includes drainage structures such as inlets and culvert ends and devices such as grates used to enhance safety of these features. impact angle The angle between the normal direction of traffic and the approach path of a test vehicle into the test article. The test article should be oriented as it would typically be in service with respect to the normal direction of traffic. impact point The initial point on a test article contacted by the impacting test vehicle. longitudinal barrier A device whose primary functions are to prevent vehicular penetration and to safely redirect an errant vehicle away from a roadside or median hazard. The three types of longitudinal barriers are roadside barriers, median barriers, and bridge rails. permanent feature (device) A feature with an anticipated long duration of service, as opposed to those used in a work or construction zone having a relatively short duration of service. support structure A system used to support a sign panel, chevron panel, lumi- naire, utility lines, mailbox, or emergency call box. The system includes the post(s), pole(s), structural elements, foundation, breakaway mechanism if used, and accompanying hardware used to support the given feature. temporary feature (device) A feature used in a work, construction, or mainte- nance zone. Its duration of use is normally relatively short, usually 1 year or less. test level A set of conditions, defined in terms of vehicular type and mass, ve- hicular impact speed, and vehicular impact angle, that quantifies the impact severity of a matrix of tests. test vehicle A commercially available, production model vehicle or an approved surrogate vehicle used in a crash test to evaluate the impact performance of a test article.

APPENDIX B 127 truck-mounted attenuator (TMA) An energy absorbing device attached to the rear of a truck or utility vehicle. A TMA is designed to provide a controlled stop of a vehicle impacting the rear of the truck. utility pole A support structure used to support power transmission lines or com- munication lines. work zone traffic control device A device used in a work zone to regulate, warn, and guide road users and advise them to traverse a section of highway or street in the proper manner. Work zone traffic control devices of interest herein include signs, plastic drums, and lights that may be used thereon; cones, barricades, chevron panels, and their support system; and any other such device(s) commonly exposed to traffic that may pose a hazard to oc- cupants of a vehicle and/or to work zone personnel. SOURCE: Excerpted from NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. H. E. Ross, Jr., D. L. Sicking, R. A. Zimmer, and J. D. Michie. TRB, National Research Council, Washington, D.C., 1993, pp. 130–131. BOX B-1 Continued FIGURE B-2 Roadside safety devices. SOURCE: GAO 2016, 4.

128 PERFORMANCE EVALUATION OF GUARDRAIL END TREATMENTS REFERENCES Abbreviations AASHTO American Association of State Highway and Transportation Officials FHWA Federal Highway Administration GAO Government Accountability Office AASHTO. 2009. Manual for Assessing Safety Hardware 2009. AASHTO, Washington, D.C. FHWA. 2015. Roadside Terminals. Nov. 14. http://safety.fhwa.dot.gov/roadway_dept/policy_ guide/road_hardware/resource_charts/roadside_terminals.pdf. GAO. 2016. Highway Safety: More Robust DOT Oversight of Guardrails and Other Road- side Hardware Could Further Enhance Safety. GAO-16-575. Washington, D.C., June. Joint AASHTO-FHWA Task Force on Guardrail Terminal Crash Analysis. 2015. Safety Analysis of Extruding W-Beam Guardrail Terminal Crashes. https://www.fhwa.dot.gov/ guardrailsafety/safetyanalysis. Ross, H. E., Jr., D. L. Sicking, R. A. Zimmer, and J. D. Michie. 1993. NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. TRB, National Research Council, Washington, D.C. FIGURE B-3 Configuration of vehicle and device at impact for crash tests of guard- rail end treatments. NOTE: The diagram depicts four of the nine tests specified in the source for guard- rail end treatments. SOURCE: Ross et al. 1993, 22. � TERMINAL OR CRASH CUSHKIN LENGT * % -H--E++ - :=-m�=: 1v c:J c:::i l 0 = 0 DEG. Y ... OFFSET • W/4 TEST NO 30 NORMAL DIRECTION Of TRAFFIC . RMINAL OR CR.OSH CUSHION LENG � c=nc=:::iT � ++±-+-+ - - . - % • c:::i c:::i l 0 = 0 DEG. OFFSET = 0 TEST NO 31 NORMAL DIRECTION Of TRAFFIC TERMINAL OR CRASH CUSHION LENGTH 0 = 15 DEG. OFFSET = 0 NORMAL DIRECTION OF TRAFFIC TEST Nos 32 AND 33 NOTE: RECOMMENDED OFFSET TOLERANCE FOR ALL TESTS = ±0.05(W)