In Reply Refer To: HSA-10/B-137B

400 Seventh St., S.W. 

April 3, 2006 Washington, D.C. 20590

Mr. Bill Neusch 

President 

Gibraltar 

320 Southland Road 

Burnet, Texas 78611 

Dear Mr. Neusch: 

In your March 2, 2006, letter to Mr. Richard Powers of my staff, you provided summary 

information on two additional tests you ran on your test level 4 (TL-4) Gibraltar cable barrier 

system and requested the Federal Highway Administration’s (FHWA) acknowledgment and 

acceptance of the test results. On March 9, 2006, you sent him complete copies of the January 

6, 2006, reports prepared by Karco Engineering, LLC (Test Report Nos. TR-P26021-01-A and 

TR-P26028-01-B) and digital videos that documented the results of these tests. Both tests were 

run on your TL-4 design in which the cables are 20, 30, and 39 inches above the ground. The 

support posts were C-posts 3.25 inches by 2.5 inches by 0.15 inches by 4.9-feet long. Each 

post was set in a 15-inch deep socket placed in a 42-inch deep by 12-inch diameter reinforced 

concrete footing. The shape and the dimensions of the steel “hairpin” and lock plate that hold 

the cables in place were slightly modified from your earlier design and are shown in Enclosure 

1. For both tests, the total installation length was 305 feet and the cables were tensioned to 

5700 pounds. 

For the first test, the line posts were set on 10-foot centers and the reported dynamic deflection 

was 6.8 feet. For the second test, the posts were spaced on 30-foot centers, resulting in 9.3 feet 

of deflection. The summary sheets for both of these tests are shown as Enclosure 2. I concur 

with the test agency’s assessment that both tests met the appropriate evaluation criteria for 

National Cooperative Highway Research Program Report 350 test 3-11, and either design may 

be used on the National Highway System when such use is acceptable to the contracting 

agency. In your March 29, 2006, follow-up letter, you requested confirmation that either 

6.25-foot long posts (for TL-3) or 7-foot long C-posts (for TL-4), driven directly into the soil 

to a depth of 42-inches, could be used as an alternative to the tested socketed posts. Since the 

longer posts were successfully used in the June 20, 2005, TL-3 test referenced below and in 

your earlier TL-4 test, I agree that either the driven or the socketed post design may be used. 

 
2

Based on a straight-line interpolation of the dynamic deflection distances noted above, you 

also requested FHWA concurrence in assumed deflections based on intermediate post 

spacings, i.e., post spacings between 10 feet and 30 feet. In reviewing our earlier acceptance 

letters for the 

Gibraltar system, we noted that for your original TL-3 design with a 15-foot post spacing, the 

reported dynamic deflection was approximately 8.5 feet. A test conducted for you by Karco on 

June 20, 2005, on a slightly modified design resulted in a reduced dynamic deflection of 

7.75 feet. Because both test installations were shorter in those tests (only 200 feet) and the 

tension in the cables was less (4800 lbs.), a direct comparison with your two recent tests cannot 

be made. However, the predicted deflections based on a straight-line interpolation between the 

10- and 30-foot post spacing deflections appear reasonable. Thus, with your TL-4 design, the 

assumed deflections with a 12-foot post spacing would be approximately 7 feet, those with a 

20-foot spacing would be approximately 8 feet, and those with a 30-foot spacing would be 

approximately 9 feet. 

As noted in my original acceptance letter B-137, dated June 13, 2005, dynamic deflection 

distances based on a single standardized test are not precise and represent only an 

approximation of what is likely to be seen in the field. Many deflections will be less, but some 

will be significantly greater, depending on actual crash conditions. Assuming test deflections 

are accurate to the nearest inch and designing a barrier installation accordingly presumes a 

degree of precision that simply does not exist. To increase the factor of safety afforded the 

motoring public, the available deflection distance should exceed the design deflection distance 

for a flexible or semi-flexible barrier system whenever practicable. 

 Sincerely yours, 

 /original signed by/ 

 John R. Baxter, P.E. 

 Director, Office of Safety Design 

 Office of Safety 

2 Enclosures 
10.0000 [254.00]

9.0000 [228.60]

2.0000 [50.80]

2.0000 [50.80]

2.5000 [63.50]

3.3750 [85.72]

.325"x.75"x 1.50" STL PLT.-WELDED

1.0000 [25.40]

2.5000 [63.50]

2.5000 [63.50]

0.7500 [19.05]

-TYP.

R0.5625 [R14.29]

-TYP.

.75" CABLE

R0.9375 [R23.81]

-TYP.

5.0000 [127.00]

5.0000 [127.00]

5.0000 [127.00]

5.0000 [127.00]

2.0000 [50.80]

2.0000 [50.80] 2.5000 [63.50]

3.3750 [85.72]

.325"x.75"x 1.50" STL PLT.-WELDED

1.0000 [25.40]

.75" CABLE

R0.5625 [R14.29]

-TYP.

R0.9375 [R23.81]

-TYP.

2.5000 [63.50]

2.5000 [63.50]

2.3750 [60.33]

2.0000 [50.80]

12.3750 [314.32]

.4375" 

ROUND BAR

.4375" 

ROUND BAR

7.5000 [190.50]

2.5000 [63.50]

0.7500 [19.05]

-TYP.

9.0000 [228.60]

10.0000 [254.00]

6.5000 [165.10]

2.5000 [63.50]

2.3750 [60.33]

2.0000 [50.80]

21.3750 [542.92]

R0.6875 [R17.46]

R0.6875 [R17.46]

R1.0000 [R25.40]

1.5000 [38.10]

1.5000 [38.10] 0.1250 [3.18]

0.1250 [3.18]

R1.0000 [R25.40]

0.5000 [12.70]-TYP.

0.5000 [12.70]-TYP.

7.5000 [190.50]

0.3750 [9.52]

TL-4 HAIRPIN AND LOCKPLATE

TL-3HAIRPIN AND LOCKPLATE

PART # 4-L29 PART # 4-L30

PART # 3-L03 PART # 3-L04

[8.255x19.05x38.1] STL PLT.-WELDED

[8.255x19.05x38.10] STL PLT.-WELDED