In Reply Refer To: 

HSA-10/B137C 

400 Seventh St., S.W. 

Washington, D.C. 20590

 July 12, 2006 

 Mr.Bill Neusch 

 President, Gibraltar 

 320 Southland Road 

 Burnet, Texas 78611

Dear Mr. Neusch: 

In your June 22, 2006, letter, you requested the Federal Highway Administration's (FHWA’s) 

concurrence that your TL-4 cable barrier system would be acceptable as a National 

Cooperative Highway Research Program (NCHRP) Report 350 test level 3 (TL-3) traffic 

barrier when placed as described below on a side slope as steep as 1V: 4H. At that time, you 

also provided staff members with preliminary test results. On July 11, Mr. Powers received a 

test report prepared by KARCO Engineering, LLC, entitled “Crash Test Report for Gibraltar 

TL-4 Cable Barrier System Installed on a 4:1 Sloped Median” and dated June 12, 2006. 

 

In my letter dated September 9, 2005, the FHWA accepted a modified Gibraltar cable barrier 

system as a TL-4 design. This design consisted of three, 3/4-inch diameter 3 X 7 posttensioned galvanized steel cables supported by steel C-posts 3.25 x 2.5 x 0.15-inches thick and 

7-ft long. These posts were driven to a depth of 3.5 feet and installed on alternate sides of the 

cables. The 3 cables are locked in place by a 7/16-inch diameter x 24-inch long galvanized 

steel hairpin and lock plate that fits inside each post. For your TL-4 design, the bottom, 

middle, and top cable heights are set at 20 inches, 30 inches, and 39 inches, respectively. 

 

A total of four tests were conducted with the TL-4 Gibraltar cable installed in a 7.3-m (24-feet) 

wide depressed median with 1V: 4H side slopes. For the first test, the barrier was located 

2.7 m (9 feet) up the slope from the ditch bottom and the test vehicle crossed the ditch bottom 

and started up the backslope before impacting the barrier. For the remaining tests (NCHRP 

Report 350 tests 3-10 and 3-11), the barrier was located down the foreslope, 1.2 m (4 feet) 

from the edge of pavement. For the first two tests, all line posts were on 30-foot centers. 

 

The first test was a modified 3-10 test in which a Geo Metro weighing 874 kg (1926 lb) was 

directed into the median at a 25° angle and 104.7 km/hr (65.1 mph), went down the slope, 

across the ditch bottom [located 3.7 m (12 ft) from edge of pavement] and 2.7 m 

(9 feet) up the far side of the ditch where it then impacted the backside of the cable [located 

8.5 m (21 ft) from edge of pavement] at 97.5 km/hr (60.6 mph). The vehicle deflected the 

barrier 1.5 m (4.9 ft) laterally and was safely contained and redirected by the Gibraltar cable. 

 
2

Enclosure 1 is the summary sheet for this test. 

The second test was a standard NCHRP Report 350 3-11 test, with the Gibraltar cable, again 

with a 30-foot post spacing, located 1.2 m (4 ft) down the 1V: 4H slope from the edge of 

pavement. A Chevrolet C2500 3/4-ton pickup truck weighing 2,038 kg (4,494 lb) impacted the 

barrier at a 25-degree angle at 98.7 km/hr (61.3 mph). The maximum dynamic deflection of 

the barrier was not reported. Although the barrier contained the vehicle, cable deflection 

allowed the pickup truck to impact the backslope of the ditch and it subsequently overturned as 

it was being redirected by the cable. This test clearly demonstrated that adverse terrain behind 

a barrier can cause significant instability when barrier deflection allows an impacting vehicle to 

reach it, even when the barrier itself prevents penetration. Enclosure 2 is the test summary 

sheet for this test. 

The third test was a repeat of the failed test, but the post spacing was reduced to 20 feet, and a 

heavier test vehicle was used, specifically a Dodge Ram 1500 weighing 2222 kg (4898 lbs). 

This is the new vehicle currently proposed for use in the draft Report 350 update. Impact 

conditions were 25 degrees and 97 km/h (60.3 mph). In this test, the pickup truck was 

contained and redirected upright with a maximum cable deflection of 2.6 m (8.6 ft). Test 

results are shown in Enclosure 3. 

The final test was a standard NCHRP Report 350 3-10 test with the Gibraltar cable again 

located 1.2 m (4 ft) down the 1V: 4H slope from the edge of pavement. A Geo Metro 

weighing 919 kg (2,026 lb) impacted the barrier at a 20-degree angle at 101.6 km/hr (63.2 

mph). The maximum dynamic deflection of the barrier was 1.4 m (4.7 ft), and the vehicle was 

safely contained and redirected by the cable. Enclosure 4 is the test summary sheet for this 

test. 

Based on the test results summarized above, your TL-4 Gibraltar cable design is acceptable as 

a TL-3 traffic barrier when placed no farther than 1.2 m (4 feet) down a 1V: 4H slope (for 

adjacent traffic impacts) and no closer than 9 feet from the ditch bottom for opposite-side 

impacts. This offset may be decreased to 8 feet based on computer simulation done by the 

National Crash Analysis Center on the generic cable barrier and on our review of the vehicle 

position at that point in your test, provided the maximum down-slope offset remains at 4 feet. 

Although the tested design was your TL-4 system (successfully tested previously with the 

single unit truck on a flat slope), transportation agencies using this design on a 1V: 4H slope 

should understand that it has been tested only to TL-3 when installed on such a slope. Thus, it 

remains possible that the single-unit TL-4 truck may not be captured or contained by the 

barrier when installed on a 4:1 slope. 

 

Sincerely yours, 

/original signed by John R. Baxter/ 

 

John R. Baxter, P.E. 

 Director, Office of Safety Design 

 Office of Safety 

 4 Enclosures 
13 

DATA SHEET NO. 2 

SUMMARY OF RESULTS FOR TEST NO. P26133-01 (MODIFIED 3-10) 

GENERAL INFORMATION OCCUPANT R

TEST AGENCY KARCO ENGINEERING FLAIL SPACE VELOCITY 

TEST NO. Modified 3-10 X-DIRECTION 

DATE 06/12/06 Y-DIRECTION 

TEST ARTICLE THIV (optional) 

TYPE Gibraltar Cable Barrier System RIDEDOWN ACCELERATIO

INSTALLATION LENGTH (m) 91.44 m (300 ft.) X-DIRECTION 

SIZE AND/OR DIMENSION OF KEY ELEMENTS 3⁄4 in 3 X 7 cable on 30 ft. post spacings Y-DIRECTION 

SOIL TYPE AND CONDITION 4:1 slope (upslope 25°) PHD (optional) 

TEST VEHICLE 820C ASI (optional) 

TYPE Production TEST ARTICLE DEFLECTIO

DESIGNATION 3-10 DYNAMIC 

MODEL Geo Metro PERMANENT 

MASS (CURB) 799 kg (1762 Ibs) VEHICLE DAMAGE 

MASS (TEST INERTIAL) 812 kg (1790 Ibs) EXTERIOR 

DUMMY(s) MASS 75 kg (165 lbs) VDS 

GROSS STATIC WEIGHT 874 kg (1926 Ibs) CDC 

IMPACT CONDITIONS INTERIOR 

SPEED (km/h) 104.7 km/h (65.08 mph) 97.51 km/h (60.60 mph) at impact OCDI 

ANGLE (Deg.) 25 

IMPACT SEVERITY (kJ) 34.8 POST-IMPACT VEHICULAR B

EXIT CONDITIONS MAXIMUM ROLL ANGLE 

SPEED (km/h) N/A* MAXIMUM YAW ANGLE (

ANGLE (Deg.) N/A* MAXIMUM PITCH ANGLE 

 * Vehicle remained in contact with the cable barrier for the duration of the event.
28 

DATA SHEET NO. 6 

SUMMARY OF RESULTS FOR TEST NO. P26133-02 (Test 3-11)

GENERAL INFORMATION OCCUPANT R

TEST AGENCY KARCO ENGINEERING FLAIL SPACE VELOCIT

TEST NO. 3-11 X-DIRECTION 

DATE 06/12/06 Y-DIRECTION 

TEST ARTICLE THIV (optional

TYPE Gibraltar Cable Barrier System RIDEDOWN ACCELERA

INSTALLATION LENGTH (m) 91.44 m(300 ft.) X-DIRECTION 

SIZE AND/OR DIMENSION OF KEY ELEMENTS 3⁄4 in 3 X 7 cable on 30 ft. post spacings Y-DIRECTION 

SOIL TYPE AND CONDITION 4:1 slope PHD (optional

TEST VEHICLE 2000P ASI (optional) 

TYPE PRODUCTION TEST ARTICLE DEFLEC

DESIGNATION 3-11 DYNAMIC 

MODEL 2500 PERMANENT 

MASS (CURB) 2210 kg (4872 Ibs) VEHICLE DAMA

MASS (TEST INERTIAL) 2038 kg (4494 Ibs) EXTERIOR 

DUMMY(s) MASS N/A VDS 

GROSS STATIC WEIGHT N/A CDC 

IMPACT CONDITIONS INTERIOR 

SPEED (km/h) 98.65 km/h (61.31 mph) OCDI 

ANGLE (Deg.) 25 

IMPACT SEVERITY (kJ) 89.5 POST-IMPACT VEHICULA

EXIT CONDITIONS MAXIMUM ROLL ANG

SPEED (km/h) N/A* MAXIMUM YAW ANGL

ANGLE (Deg.) N/A* MAXIMUM PITCH ANG

* Vehicle rolled over on the cable barrier.
44 

DATA SHEET NO. 10 

SUMMARY OF RESULTS FOR TEST NO. P26133-03 (Test 3-11) 

GENERAL INFORMATION OCCUPANT RISK V

TEST AGENCY KARCO ENGINEERING FLAIL SPACE VELOCITY (m/se

TEST NO. 3-11 X-DIRECTION 

DATE 06/14/06 Y-DIRECTION 

TEST ARTICLE THIV (optional) 

TYPE Gibraltar Cable Barrier System RIDEDOWN ACCELERATION (g

INSTALLATION LENGTH (m) 92.9 m(305 ft.) X-DIRECTION 

SIZE AND/OR DIMENSION OF KEY ELEMENTS 3⁄4 in 3 X 7 cable on 20 ft. post spacings Y-DIRECTION 

SOIL TYPE AND CONDITION 4:1 slope(down slope 25°) PHD (optional) 

TEST VEHICLE 2270P ASI (optional) 

TYPE Production TEST ARTICLE DEFLECTIONS (

DESIGNATION 3-11 DYNAMIC 

MODEL RAM 1500 PERMANENT 

MASS (CURB) 2194 kg (4836 Ibs) VEHICLE DAMAGE 

MASS (TEST INERTIAL) 2222 kg (4898 Ibs) EXTERIOR 

DUMMY(s) MASS N/A VDS 

GROSS STATIC WEIGHT N/A CDC 

IMPACT CONDITIONS INTERIOR 

SPEED (km/h) 97.05 km/h (60.32 mph) OCDI 

ANGLE (Deg.) 25 

IMPACT SEVERITY (kJ) 144.7 POST-IMPACT VEHICULAR BEHA

EXIT CONDITIONS MAXIMUM ROLL ANGLE (Deg

SPEED (km/h) N/A* MAXIMUM YAW ANGLE (Deg.

ANGLE (Deg.) N/A* MAXIMUM PITCH ANGLE (Deg

 * Vehicle remained in contact with the cable barrier for the duration of the event.
61 

DATA SHEET NO. 14 

SUMMARY OF RESULTS FOR TEST NO. P26133-04 (Test 3-10) 

GENERAL INFORMATION OCCUPANT RISK VALUES 

TEST AGENCY KARCO ENGINEERING FLAIL SPACE VELOCITY (m/sec) 

TEST NO. 3-10 X-DIRECTION 

DATE 06/16/06 Y-DIRECTION 

TEST ARTICLE THIV (optional) 

TYPE Gibraltar Cable Barrier System RIDEDOWN ACCELERATION (g’s) 

INSTALLATION LENGTH (m) 91.44 m (300 ft.) X-DIRECTION 

SIZE AND/OR DIMENSION OF KEY ELEMENTS 3⁄4 in 3 X 7 cable on 30 ft. post 

i

Y-DIRECTION 

SOIL TYPE AND CONDITION 4:1 slope (upslope 25°) PHD (optional) 

TEST VEHICLE 820C ASI (optional) 

TYPE PRODUCTION TEST ARTICLE DEFLECTIONS (m) 

DESIGNATION 3-10 DYNAMIC 

MODEL Geo Metro PERMANENT 

MASS (CURB) 858 kg (1892 Ibs) VEHICLE DAMAGE 

MASS (TEST INERTIAL) 845 kg (1862 Ibs) EXTERIOR 

DUMMY(s) MASS 75 kg (165 lbs) VDS 

GROSS STATIC WEIGHT 919 kg (2026 Ibs) CDC 

IMPACT CONDITIONS INTERIOR 

SPEED (km/h) 101.63 km/h (63.16 mph) OCDI 

ANGLE (Deg.) 20 

IMPACT SEVERITY (kJ) 39.3 POST-IMPACT VEHICULAR BEHAVIOR 

EXIT CONDITIONS MAXIMUM ROLL ANGLE (Deg.) 

SPEED (km/h) N/A* MAXIMUM YAW ANGLE (Deg.) 

ANGLE (Deg.) N/A* MAXIMUM PITCH ANGLE (Deg.) 

*Test vehicle exit conditions occurred beyond the view of the overhead cameras.