- Briefing Room
U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
FHWA Review of ET-Plus
Anchor: The mechanism that fixes the ends of a run of guardrail to the ground, providing rail tension in the event of a LON impact.
Channel, Feeder Channels: The portion of the extruder head that aligns the device with the w-beam rail. (The ET-plus terminal head was made with feeder channels that were 5 inches wide or 4 inches wide.)
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.
Errant Vehicle: A vehicle that leaves the traveled way, typically at speed, and encroaches onto the roadside.
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. Examples of extruding terminals are the ET-2000, ET-Plus, SKT, and FLEAT.
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. 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. It may or may not have a crashworthy guardrail terminal. Non-crashworthy terminals include the blunt-end, turn-down terminal, Breakaway Cable Terminal (BCT), and Modified Eccentric Loader Terminal (MELT).
Guardrail Face, Guardrail Run: The length-of-need portion of a guardrail installation.
Guardrail Terminal, Guardrail End Terminal, Guardrail End Treatment, Crashworthy 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. Guardrail terminals examined in this study included the ET-2000, ET-Plus, Sequential Kinking Terminal (SKT), and Flared Energy Absorbing Terminal (FLEAT).
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: Crash involving a vehicle that exceeds the 4400-pound mass of the —-ton pickup truck specified for crash testing of guardrail terminals 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 (LON): 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 calculated or presumed path.
Non-Tracking: 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.
Occupant Compartment Deformation: Event that occurs when the force of a guardrail impact deforms the interior structure of a vehicle's passenger area. Injuries can result from occupant contact with the intruding structure.
Occupant Compartment Penetration: Event that involves a portion of the guardrail entering or penetrating into the passenger area of the vehicle. Injuries can result from occupant contact with the penetrating rail.
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 crashworthiness, 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. Rollovers have a high incidence of occupant ejection from the vehicle or head trauma from flail within the vehicle.
Shallow-Angle Impact: Frontal impact into a guardrail terminal where the travel direction of the vehicle is nearly parallel (approximately ten 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 non-tracking events where the vehicle may be sliding at an angle or yawing.
Snagging: The undesirable interaction of vehicle components with a barrier face or posts during impact due to deflection and/or surface irregularities in the barrier. Parts of the vehicle may be sheared off, or the vehicle may decelerate abruptly, spinout, or rollover. Severe snagging during impact with a w-beam barrier or terminal may lead to rail separation and failure of the barrier to contain the vehicle.
Spearing: Guardrail penetrating the exterior of an impacting vehicle and potentially penetrating into the occupant compartment.
Sudden Deceleration: This eventinvolves forces exerted when a vehicle is slowed down abruptly or brought to a sudden stop through contact with the guardrail, potentially resulting in injuries to passengers.
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.
Yaw, Yawing: The rotation of an out-of-control vehicle skidding on the pavement or roadside.
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