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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-122

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U.S. Department of Transportation
Federal Highway Administration

1200 New Jersey Ave. S.E.
Washington, D.C. 20590

December 19, 2011

In Reply Refer To: HSST/CC-122

Mr. Barry D. Stephens, P.E.
Sr. Vice President Engineering
Energy Absorption Systems
3617 Cincinnati Avenue
Rocklin, CA  95678

Dear Mr. Stephens:

This letter is in response to your request for the Federal Highway Administration (FHWA) to review a roadside safety system for eligibility for reimbursement under the Federal-aid highway program.

Name of system: Trinity End Terminal Median (TREND™ 350 Median)
Type of system:

W-Beam Redirective, Gating End Terminals

Test Level: NCHRP Report 350 Test Level 3 (TL-3)
Testing conducted by: E-Tech Testing Services, Inc.
Date of request: December 17, 2010
Request acknowledged: October 26, 2011
Task Force 13 Designator: SEW26; TREND™ 350 Median

Based on a review of crash test results submitted by the manufacturer certifying the device described herein meets the crashworthiness criteria of the National Cooperative Highway Research Program (NCHRP), Report 350 testing guidelines the device is eligible for reimbursement under the Federal-aid highway program.  Eligibility for reimbursement under the Federal-aid highway program does not establish approval or endorsement by FHWA for any particular purpose or use.

The FHWA, the Department of Transportation, and the United States Government do not endorse products or services and the issuance of a reimbursement eligibility letter is not an endorsement of any product or service

Requirements
Roadside safety devices should meet the guidelines contained in the National Cooperative Highway Research Program Report 350 (NCHRP Report 350).  The FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 24, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Decision
The following device was found eligible, with details provided below:

Description
The TREND™ 350 End Terminal family of products includes the TREND™ 350 Median.  This new family of products is designed to shield the end of w‑beam guardrail in both roadside tangent and flared installations and double sided median installations.  The tangent and flared systems are constructed from the same components with the only difference being the product’s installation with or without a flare relative to the edge of road.  The double-sided median system uses many of the same components as the TREND™ 350 Tangent and Flared system; however the head, head rails and rail spacers are unique to allow attachment to double-faced guardrail found in roadway medians.  The beginning of length of need (BLON) for this system is cited as the third post.  It should be noted that the rail and anchorage components showed their ability to redirect impacting vehicles at flare angles of up to 6 degrees during the TREND™ 350 End Terminal, Tangent and Flared test series.  Since the TREND™ 350 Median system is composed of the same structural elements, this system can be installed with a flare of up to 6 degrees, which corresponds to 3 feet 6 inches for the 5 post system and 2 feet 10 inches for a system that is 4 posts in length. 

The TREND™ 350 Median is based on AASHTO w‑beam rail that has been modified to include slots.  These slots extend the length of the rail from the guardrail bolts that hold the rail together.  When an errant vehicle strikes the impact head of the terminal in an end on impact, the vehicle’s energy is safely absorbed by the terminal’s rail sections as each of the adjacent pairs of rail sections slide past each other.  The vehicle’s kinetic energy is dissipated by tearing of the panel slots, re-shaping of the panels by a calibrated fin at the back of each panel, and by friction.  A lightweight impact head is attached to the front of the unit to engage impacting vehicles and to control potential vehicle spearing by the downstream guardrail.

The TREND™ 350 Median uses end terminal posts and anchorage components that were previously tested to NCHRP 350.  These posts designs, known as the Hinged Breakaway Assembly (HBA) and Steel Yielding Terminal Post (SYTP), have seen extensive use in the ET family of end terminals previously accepted by the FHWA.  The TREND™ 350 Median uses an HBA post in the first post position and an SYTP post in the second post position.  These first two posts are joined together by another standard end terminal component, the Angle Strut.  The remaining system posts are standard line posts, proven in a number of products.  The TREND™ 350 Median uses two line posts, resulting in total length of 26 feet 11 inches.  Past FHWA  letters for the above cited components are HSA-10/CC-12F (HBA and Angle Strut), HSA-10/CC-12L (W6X8.5 SYTP), and HAS‑10/CC-12Q (ET with line posts).

Details of this system are included as an enclosure to this correspondence.

Crash Testing
The following NCHRP Report 350 tests were completed for FHWA review of the TREND Median End Terminal:

TREND™ 350 Median End Terminal:

Impact speed = 97.0 km/h, Long. ΔV = 11.3 m/s, Long. Ridedown = -18.4 g

Impact speed = 96.4 km/h, Long. ΔV = 8.2 m/s, Long. Ridedown = -11.3 g

Impact speed = 100.4 km/h, Long. ΔV = 8.4 m/s, Long. Ridedown = -10.2 g

Tests 3-32 through 3-35 and Test 3-39 were not run for the TREND™ 350 Median as the manufacturer requests these tests be waived based upon the following reasons, as stated in Table 1. In addition, it is noted that Test 3-31 for the TREND™ 350 Median End Terminal was conducted twice.  This test was first run with a system that had a total five (5) posts at 33 feet 2 inches in length.  This test demonstrated that the system had excess capacity and therefore Test 3-31 was re-conducted with a system that had a total of four (4) posts at 26 feet 11 inches in length.  As noted above, this test also resulted in satisfactory occupant risk values.

Test summaries of the above tests are included as an enclosure to this correspondence.

Table 1.  Trinity End Terminal (TREND™ 350), Test Matrix

Test # Illustration Completed Notes
3-30 Terminus 350, MedianTest Matrix Model (1).jpg YES Passed all Occupant Risk Values.
3-31 (1) Terminus 350, MedianTest Matrix Model (1).jpg YES 5-Bay System
Passed all Occupant Risk Values.
3-31 (2) Terminus 350, MedianTest Matrix Model (1) YES 4-Bay System
Passed all Occupant Risk Values.
3-32 Terminus 350, MedianTest Matrix Model (1).jpg

 

NO Test 3-30, which was run on the TREND™ 350 Median, is worst case for a gating energy absorbing terminal.  Test 3‑32 was run on the single sided system in the tangent configuration and this test need not be re-run.
3-33 Terminus 350, MedianTest Matrix Model (1).jpg NO Test 3-31, which was run on the TREND™ 350 Median is worst case for a gating energy absorbing terminal.  Test 3‑33 was run on the single sided system in the tangent configuration and this test need not be re-run.
3-34  

Terminus 350, MedianTest Matrix Model (1).jpg

NO This test was passed on the single sided system in the tangent configuration. The single sided system test is worst case, as there are less structural elements resisting the impact.
3-35 Terminus 350, MedianTest Matrix Model (1).jpg NO This test was passed on the single sided TREND™ 350 End Terminal installed in both the flared and tangent configurations.  These single sided system tests are worst case, as there are less structural elements resisting the impact.
3-39 Terminus 350, MedianTest Matrix Model (1).jpg NO This test was passed on the single sided TREND™ 350 End Terminal in the tangent configuration and the structural elements the vehicle impacts have not changed.  The single sided system test is worst case, as there are less structural elements resisting the impact.

Findings
Based on the successful completion of the described NCHRP Report 350 testing, FHWA  concurs that the TREND™ 350 Median End Terminal meets the evaluation criteria for NCHRP Report 350 redirective, gating end terminals at TL-3 impact conditions.  The FHWA also concurs with the request for a testing waiver of NCHRP Report 350 test numbers 3-32, 3-33, 3-34, 3-35, and 3-39 and the provided reasons for the waiver for each of these test numbers as stated within this correspondence.

In addition, FHWA concurs that the testing of the TREND™ 350 End Terminal family of end terminals was conducted at the worst-case guardrail height of 27-3/4 inches and it is acceptable to use the TREND™ 350 Median End Terminal when attached to guardrail with heights between 27-3/4 inches and 31 inches (SGM04a-b from 27 ¾ inches to 30 inches, MGS from 27 ¾ inches to 31 inches, and the various proprietary 31-inch designs.)

The FHWA also notes that the rail and anchorage components showed their ability to redirect impacting vehicles at flare angles of up to 6 degrees during the TREND™ 350 End Terminal, Tangent and Flared test series.  Since the TREND™ 350 Median system is composed of the same structural elements, this system can be installed with a flare of up to 6 degrees, which corresponds to 3 feet 6 inches for the 5 post system and 2 feet 10 inches for a system that is 4 posts in length. 

Therefore, these systems as described are eligible for reimbursement and should be installed under the range of conditions tested, when such use is acceptable to a highway agency.
Please note the following standard provisions that apply to the FHWA eligibility letters:

 

Sincerely yours,

/* Signature of Michael S. Griffith */
Michael S. Griffith
Director, Office of Safety Technologies
Office of Safety

Enclosures

Page last modified on January 17, 2013.
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