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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-177

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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)
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:

  1. NCHRP Report 350 Test 3-10, (820C, 100 km/hr, 20 degrees) and
  2. MASH-08 Test 3-11 (2270P, 100 km/hr, 25 degrees)

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,

Signature of David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

Enclosure


Images of car crashing into guardreail
General Information
Test AgencyTexas Transportation
Test No.400001-TGS2
Test Date06-08-2007
Test Category3-10 Update
Test Article
TypeLongitudinal Barrier
NameTrinity Guardrail System (TGS)
Total Installation Length175 ft
Key Elements
DescriptionW-Beam on W6x8.5 x 72 inch
long posts, splices at posts, no
blockouts, no flange protectors
Soil Type and ConditionStandard Soil, Damp (9.8%)
Test Vehicle
Type/Designation820C
Make/Model1997 Chevrolet Metro
Mass
Curb1832 lb
Test Inertial1830 lb
Dummy170 lb
Gross Static2000 lb
Impact Conditions
Speed61.1 mi/h
Angle19.7 degrees
Location/OrientationBtw Post 11 and 12
Exit Conditions
Speed28.8 mi/h
Angle9.3 degrees
Post Impact Trajectory
Vehicle StabilitySatisfactory
Stopping DistanceBtw Post 21 and 22
6 ft laterally front
Vehicle SnaggingNone
Vehicle PocketingNone
Post-Impact Behavior (during 1.0 sec after impact)
Max. Yaw Angle26 degrees
Max. Pitch Angle-6 degrees
Max. Roll Angle13 degrees
Test Article Deflections
Dynamic19.4 inches
Permanent9.6 inches
Working Width22.2 inches
Occupant Risk Values
Impact Velocity
Longitudinal28.2 ft/s
Lateral17.7 ft/s
Ridedown Accelerations
Longitudinal-120 gs
Lateral-7.7 gs
THIV23.5
PHD13.0 gs
Max. 0.050-s Average
Longitudinal-9.7 gs
Lateral-6.3 gs
Vertical-2.5 gs
Vehicle Damage
VDS01RFQ4
CDC01FREW3
Max Exterior
Vehicle Crash11.8 inches
OCDI
Max. Occupant CompartmentRF0010000
Deformation5.5 inches

Figure 6.7. Summary of results for NCHRP Report 350 test 3-10 on the TGS.


Table 4.1 - Summary of Test Results and Conditions
Images of truck crashing into guardreail
General Information
Test AgencyTexas Transportation
Test No.400001-TGS1
Test Date05-31-2007
Test Article
TypeLongitudinal Barrier
NameTrinity Guardrail System (TGS)
Total Installation Length175 ft
Key Elements
DescriptionW-Beam on W6x8.5 x 72 inch
long posts, splices at posts, no
blockouts, no flange protectors
Soil Type and ConditionStandard Soil, Damp (9.8%)
Test Vehicle
Type/Designation2270P
Make/Model2002 Dodge Ram 1500 Pickup
Mass
Curb4726 lb
Test Inertial4970 lb
DummyNo Dummy
Gross Static4970 lb
Impact Conditions
Speed63.3 mi/h
Angle23.8 degrees
Location/OrientationBtw Post 11
Exit Conditions
Speed36.6 mi/h
Angle18.4 degrees
Post Impact Trajectory
Vehicle StabilitySatisfactory
Stopping Distance175 ft downstream
50 ft laterally front
Vehicle SnaggingNone
Vehicle PocketingNone
Post-Impact Behavior (during 1.0 sec after impact)
Max. Yaw Angle-37 degrees
Max. Pitch Angle2 degrees
Max. Roll Angle-13 degrees
Test Article Deflections
Dynamic38.4 inches
Permanent31.0 inches
Working Width40.9 inches
Occupant Risk Values
Impact Velocity
Longitudinal16.1 ft/s
Lateral16.7 ft/s
Ridedown Accelerations
Longitudinal-11.2 gs
Lateral-7.9 gs
THIV23.5
PHD13.0 gs
Max. 0.050-s Average
Longitudinal-5.6 gs
Lateral-6.5 gs
Vertical-2.5 gs
Vehicle Damage
VDS01RFQ4
CDC01FREW3
Max Exterior
Vehicle Crash19.0 inches
OCDI
Max. Occupant CompartmentRF0000000
Deformation0.6 inch

Figure 5.7. Summary of the reults for NCHRP Report 350 Update test 3-11 on the TGS.


Image of Trinity W-Beam System
Figure 2.2. Layout of the Trinity Guardrail System (TGS)

Image of Trinity W-Beam System
Figure 2.1. Dtails of countersunk bolt.

Page last modified on June 24, 2011.
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