In Reply Refer To: HSA-10/B-148 

400 Seventh St., S.W. 

June 2, 2006 Washington, D.C. 20590

 

 Mr. Steve L. Brown 

 President 

 Trinity Highway Safety Products Division 

 P.O. Box 568887 

 Dallas, Texas 75356-8887 

Dear Mr. Brown: 

In his April 28, 2006 letter to Mr. Richard Powers, Mr. Brian Smith requested the Federal 

Highway Administration (FHWA) acceptance of a new strong post Thrie-beam guardrail 

design called the T-39. With the letter, he also sent copies of a Texas Transportation Institute 

(TTI) report dated April 2006, entitled “Testing and Evaluation of the T-39 Thrie-Beam 

Longitudinal Barrier”, and digital videos of the three tests that were run. 

The T-39 Thrie-beam guardrail uses standard 12-gauge Thrie-beam panels mounted on 

modified W6 x 8.5 steel posts with a top-of-rail height of 39 inches. The modified posts, 

called Steel Yielding Line Posts (SYLP) posts are 6-feet long and set in the ground to a depth 

of 40 inches on standard 6-ft, 3-inch centers. Each post has four 13/16-inch diameter holes in 

the flanges at the ground line. The rail is attached to each post without an offset block using a 

5/8-inch diameter x 1-3/4-inch long special bolt with a slotted countersunk head. A 6-inch 

long section of W-beam called a flange protector (backup plate) is used at each post. All 

splices in the Thrie-beam rail elements fall midspan, between adjacent posts. Design details 

for the SYLP post and its unique connection bolt are shown on Enclosure 1. Note that the top 

of the post is 32 inches above the ground and that the top of the Thrie-beam is 7 inches higher. 

The T-39 railing can be installed as a roadside barrier with rail only on the traffic side of the 

posts (as shown in Enclosure 1) or as a symmetrical median barrier with Thrie-beam mounted 

on both sides of the support posts. 

Test 3-10 was conducted using the current National Cooperative Highway Research Program 

Report 350 small car (820C) impacting the T-39 median barrier at a 20-degree angle. The 

median design was used for this test because the stiffer of the two designs was deemed more 

likely to cause the small car to impact and interact with the posts. Test 3-11 was conducted 

with a quad-cab pickup truck having a nominal weight of 2270 kg (currently proposed as the 

 
2

new test vehicle under the Report 350 update) into the roadside version of the T-39, and test 

4-11 was run using the standard single-unit truck, also into the roadside design. For the latter 

two tests, it was believed that the roadside design would be most likely to fail with the larger 

vehicles due to increased dynamic deflection. My staff agreed with these assumptions. 

Summary sheets for each of these tests are shown in Enclosure 2. 

Based on these test results, both the median and roadside versions of the T-39 guardrail, as 

described above, may be considered crashworthy under the existing Report 350 guidelines as 

test level 4 (TL-4) barriers and may be used on the National Highway System when such use is 

acceptable to the contracting authority. When new testing guidelines are formally adopted, you 

may choose to rerun the small car test at the 25-degree impact angle proposed by the 

researchers for test 3-10 since your small car test was deemed marginal (due to passenger 

compartment deformation) under the current 20-degree impact angle. Because the rail height 

exceeds that of existing metal beam guardrails, you will need to develop transition designs if 

the T-39 rail is connected to a bridge parapet or to a crashworthy W-beam terminal. Potential 

users also need to be aware that under TL-4 impact conditions, the truck box exhibited an 

estimated roll angle of over 30 degrees (the cab roll angle was reported as 12 degrees), and 

extended more than 3 feet beyond the deflected rail. This area must be kept free of rigid 

vertical objects such as overhead/cantilever sign supports and bridge piers. 

Please note the following standard provisions that apply to the FHWA letters of acceptance:

• Any changes that may adversely influence the crashworthiness of this barrier will require 

a new acceptance letter.

• Should the FHWA discover that the qualification testing was flawed, that in-service 

performance reveals unacceptable safety problems, or that the device being marketed is 

significantly different from the version that was crash tested, it reserves the right to 

modify or revoke its acceptance.

• You will be expected to supply potential users with sufficient information on design and 

installation requirements to ensure proper performance.

• You will be expected to certify to potential users that the hardware furnished has 

essentially the same chemistry, mechanical properties, and geometry as that submitted for 

acceptance. 

• To prevent misunderstanding by others, this correspondence, designated as acceptance 

letter B-148, shall not be reproduced except in full. This letter, and the test 

documentation upon which this letter is based, is public information. All such letters and 

documentation may be reviewed at our office upon request. 

• Since the T-39 guardrail is a steel product, the provisions of Title 23, Code of Federal 

Regulations, Section 635.410 apply to its use on federally funded projects.

• The T-39 guardrail includes patented components and is considered a proprietary 

product. When proprietary devices are specified by a highway agency for use on 

federally-funded projects they: (a) must be supplied through competitive bidding with 

equally suitable unpatented items; (b) the highway agency must certify that they are 

essential for synchronization with existing highway facilities or that no equally suitable 

alternative exists; or (c) they must be used for research or for a distinctive type of 
3

construction on relatively short sections of road for experimental purposes. Our 

 regulations concerning proprietary products are contained in Title 23, Code of Federal 

 Regulations, Section 635.411.

• This acceptance letter shall not be construed as authorization or consent by the FHWA to 

use, manufacture, or sell any patented device for which the applicant is not the patent 

holder. Patent issues, if any, are to be resolved by the applicant. 

 Sincerely yours, 

 /original signed by/ 

 

John R. Baxter, P.E. 

 Director, Office of Safety Design 

 Office of Safety 

2 Enclosures 
ELEVATION VIEW

PLAN VIEW

DETAIL 1

SECTION A-A

SECTION B-B

(TYPICAL SPLICE)

T-39 RAIL TO POST ASSE

44

55

66

77

88

A 

B 

C D 

1

AA

B

B

GROUND LINE

(4) HOLES n13/16"THRU IN LINE

3

'

-

3

"

3

'

-

4

"

-

E

M

B

E

D

M

E

N

T

2

'

-

1

"

7

"

GROUND LINE

12'-6" THRIE-BEAM GUARDRAIL (TYPICAL)

6'-3" POST SPACE (TYPICAL)

TYPICAL SPLICEAT MID-SPANLAP IN DIRECTIONOF TRAFFIC

DIRECTION OF TRAFFIC

6 5

3

2

5

4 3

1
17 

0.000 s 0.108 s 0.215 s 

General Information Test Agency...............................  Test No. ....................................  Date ........................................... Test Article Type...........................................  Name .........................................  Installation Length (m) ...............  Material or Key Elements .......... Soil Type and Condition............. Test Vehicle Type...........................................  Designation................................  Model.........................................  Mass (kg)  Curb........................................  Test Inertial.............................  Dummy...................................  Gross Static............................ 

Texas Transportation Institute 220570-5 11-11-2005 Median Barrier Guardrail T-39 Thrie Beam Guardrail 68.6 ThrIe Beam Guardrail on Steel Yielding Line Posts w/top of rail height of 991 mm Standard Soil, Dry Production 820C 1996 Chevrolet Metro 851 877  79 956 

Impact Conditions  Speed (km/h) .............................  Angle (deg) ................................ Exit Conditions Speed (km/h) .............................  Angle (deg) ................................ Occupant Risk Values Impact Velocity (m/s)  Longitudinal ............................  Lateral ....................................  THIV (km/h) ...............................  Ridedown Accelerations (g’s)  Longitudinal ............................  Lateral ....................................  PHD (g’s) ...................................  ASI ............................................ Max. 0.050-s Average (g’s)  Longitudinal ............................  Lateral ....................................  Vertical ................................... 

102.6  19.8 64.3  0.3  6.2  6.5 32.2 -10.3 -10.9 12.5 1.26 -9.3 -9.1 -2.3 

Test Article Deflections  Dynamic ..................... Permanent.................. Working Width............Vehicle Damage

 Exterior  VDS......................... CDC ........................ Max. Exterior  Vehicle Crush (mm Interior  OCDI ....................... Max. Occupant Com Deformation (mm) Post-Impact Behavior (during 1.0 sec after im Max. Yaw Angle (de Max. Pitch Angle (de Max. Roll Angle (deg

Summary of results for NCHRP Report 350 test 3-10 on T-39 Thrie Beam Median Barrier Guar
0.000 s 0.195 s 0.390 s 

53 

Gen nformation

T ency...............................T . ....................................D .......................................

Tes cle T .......................................

N .........................................

Installation Length (m)...............

y Elements ..........

Soil and Condition.............Test Vehicle Type........................................... Designation................................ Model......................................... Mass (kg) Curb........................................ Test Inertial............................. Gross Static............................

Texas Transportation Institute 220570-7 02-09-2006 Guardrail T-39 Thrie Beam Guardrail 68.6 ThrIe Beam Guardrail on Steel Yielding Line Posts w/top of rail height of 991 mm Standard Soil, Dry Production 2270P 2002 Dodge 1500 pickup truck 2220 2290 2290 

Impact Conditions  Speed (km/h) ............................. Angle (deg) ................................Exit Conditions Speed (km/h) ............................. Angle (deg) ................................Occupant Risk Values

Impact Velocity (m/s) 

 Longitudinal ............................ Lateral .................................... THIV (km/h) ...............................

Ridedown Accelerations (g’s) 

 Longitudinal ............................ Lateral .................................... PHD (g’s) ................................... ASI ............................................Max. 0.050-s Average (g’s)  Longitudinal ............................ Lateral .................................... Vertical ...................................

99.0 24.5 62.0  8.0  6.9  2.3 25.8  -9.9 -17.6  16.6  1.43  -5.1 -12.6  2.9 

Test Article Deflections  Dynamic ..................... Permanent.................. Working Width............Vehicle Damage Exterior  VDS......................... CDC ........................ Max. Exterior 

 Vehicle Crush (mm

 Interior  OCDI ....................... Max. Occupant Com

 Deformation (mm)

Post-Impact Behavior

(during 1.0 sec after im

 Max. Yaw Angle (de

Max. Pitch Angle (deMax. Roll Angle (deg

Figure 36. Summary of results for NCHRP Report 350 test 3-11 (updated) on T-39 Thrie Beam Gu

eral I

est Agest No

ate ....

t Arti

ype....

ame

Material or Ke

Type
29 

0.000 s 0.263 s 0.526 s 

General Information Test Agency...............................  Test No. ....................................  Date ........................................... Test Article Type...........................................  Name .........................................  Installation Length (m) ...............  Material or Key Elements .......... Soil Type and Condition............. Test Vehicle Type...........................................  Designation................................  Model.........................................  Mass (kg)  Curb........................................  Test Inertial.............................  Gross Static............................ 

Texas Transportation Institute 220570-6 01-20-2006 Guardrail T-39 Thrie Beam Guardrail 68.6 ThrIe Beam Guardrail on Steel Yielding Line Posts w/top of rail height of 991 mm Standard Soil, Dry Production 8000S 1996 Freightliner FL60 Truck 5425 8192 8192 

Impact Conditions  Speed (km/h) .............................  Angle (deg) ................................ Exit Conditions Speed (km/h) .............................  Angle (deg) ................................ Occupant Risk Values Impact Velocity (m/s)  Longitudinal ............................  Lateral ....................................  THIV (km/h) ...............................  Ridedown Accelerations (g’s)  Longitudinal ............................  Lateral ....................................  PHD (g’s) ...................................  ASI ............................................ Max. 0.050-s Average (g’s)  Longitudinal ............................  Lateral ....................................  Vertical ................................... 

78.8 15.3 N/A ~6.6  3.2  2.6 13.7 -2.0 -3.7 3.9 0.26 -1.9 -2.1  1.0 

Test Article Deflections  Dynamic ..................... Permanent.................. Working Width............Vehicle Damage

 Exterior  CDC ........................ Max. Exterior  Vehicle Crush (mmPost-Impact Behavior (during 1.0 sec after im Max. Yaw Angle (de Max. Pitch Angle (de Max. Roll Angle (deg

Summary of results for NCHRP Report 350 test 4-12 on T-39 Thrie Beam Guardrail.