U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Ave. S.E.
Washington, D.C. 20590
July 16, 2007
In Reply Refer To: HSSD/B-177
Mr. Brian Smith
Trinity Highway Products, LLC
PO Box 568887
Dallas, TX 75356-8887
Dear Mr. Smith:
This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of a roadside safety system for use on the National Highway System (NHS).
Name of system: | Trinity Guardrail System (TGS) |
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Type of system: | 31 inch strong post w-beam longitudinal barrier |
Test Level: | National Cooperative Highway Research Program (NCHRP) Report 350 and Manual for Assessing Safety Hardware 2008 (MASH-08) Test Level 3 |
Testing conducted by: | Texas Transportation Institute |
Date of request: | November 13, 2007 |
Additional information received: | April 28, 2008 |
Date of completed package: | June 20, 2008 |
You requested that we find this system acceptable for use on the NHS under the provisions of the NCHRP Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features” and the proposed American Association of State Highway and Transportation Officials’ MASH-08.
Requirements
Roadside safety systems should meet the guidelines contained in the NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features." FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers. You have also chosen to anticipate the adoption of the MASH-08, an option that the FHWA has offered with the understanding that additional testing may need to be done if changes to the test criteria are made before the MASH-08 is formally adopted.
Description
The TGS is a non-blocked-out strong post w-beam longitudinal barrier system that consists of 3.81 m (12 foot 6 inch) long, 12 gage w-beam rails supported on 1.83 m (6 foot 0 inch) long W150 x 12.6 (W6 x 8.5#) standard (non-weakened) line posts spaced 1.905 m (6 feet 3 inches) on center. Measured from the ground level the heights of the top of the posts and the top edge of the w-beam are 813 mm (32 inches) and 787 mm (31 inches) respectively. W-beam rail splices are located at the posts.
The FHWA previously accepted Trinity’s 31-inch high non-blocked-out strong post w-beam barrier that used steel yielding line posts with splices located at mid-span (FHWA Acceptance Letter B-140 dated November 2, 2005).
Crash Testing
Two full scale crash tests were conducted on a 53 m (175 foot) length of the TGS:
In both tests the rail splices were located at the posts with no Flange Protector (backup plate) in use. In test No. 1 the rails were attached to the posts with 16 mm x 44 mm (5/8 x 1 ¾ inch) slotted countersunk head bolts that were previously used in testing the Trinity T-31 and T-39 barrier systems. In test No. 2 the rails were attached to the posts with 16 mm x 44 mm (5/8 x 2 inch) countersunk head bolts with an elongated shaft. You plan on using only the 16 mm x 44 mm (5/8 x 1 ¾ inch) slotted countersunk head bolt as this bolt allowed the rail to release from the post more readily during testing.
Findings
You requested acceptance under both the NCHRP Report 350 and the MASH-08 criteria. Tests No. 1 and No. 2 noted above and detailed in the enclosed Test data summary sheets met the test and evaluation criteria of the NCHRP Report 350 and the Proposed MASH-08, respectively. At our request you provided the overhead view of test No. 1 that showed the small car redirected by the barrier through a yaw of 140 degrees. However we found no evidence of hard snagging on any post and the vehicle trajectory was comparable to that seen in other accepted barrier systems.
The MASH-08 test 3-10 of the 1100C impacting at 25 degrees was waived as previously agreed by the FHWA because of the pair of 3-10 tests conducted on the T-31 system. Those tests showed the 820C impact resulted in higher occupant impact velocities and ridedown accelerations. We concur that the 820C test is the ‘worst case scenario’ for the TGS as well.
The Report 350 Test 3-11 was waived as previously agreed by the FHWA because of the greater impact severity of the 2270 kg pickup truck. Although it is known that the 2000P vehicle is structurally less stable we concurred in your contention that the heavier truck would be most likely to fail the system due to increased dynamic deflection.
Therefore, the system described above and detailed in the enclosed drawings is acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to a highway agency. The maximum dynamic deflection measured in test 3-11 was 980 mm (38.4 inches) and the ‘working width’ was 1040 mm (40.9 inches.)
You also requested 2 m post spacing be allowed for use in countries that follow the metric system, as we permitted you to do on the T-31 and T-39 systems. As the standard USA spacing is 1.905 m we consider the 5 percent additional distance between the posts to be acceptable.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
Sincerely yours, David A. Nicol, P.E. |
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Figure 6.7. Summary of results for NCHRP Report 350 test 3-10 on the TGS.
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Figure 5.7. Summary of the reults for NCHRP Report 350 Update test 3-11 on the TGS.
Figure 2.2. Layout of the Trinity Guardrail System (TGS)
Figure 2.1. Dtails of countersunk bolt.