In Reply Refer To: 

HSA-10/B82-C1 

400 Seventh St., S.W. 

Washington, D.C. 20590 April 13, 2006 

 Mr. Derek W. Muir 

 Group Managing Director 

 Hill & Smith Ltd. 

 Springvale Business and Industrial Park 

 Bilston, Wolverhampton, West Midlands, WV14 0QL

Dear Mr. Muir: 

In my May 26, 2005, letter to you (acceptance letter B-82C), the Federal Highway 

Administration accepted a three-cable version of your original 4-strand Brifen Wire Rope 

Safety Fence (WRSF) as an National Cooperative Highway Research Program (NCHRP) 

Report 350 test level 3 (TL-3) traffic barrier. The tests referenced in that letter were run on a 

WRSF installation that was 278-m (912-ft) long with the bottom two cables interwoven 

between adjacent posts and the top cable set in a slot cut into the top of each post. Cable 

heights measured from ground level were 460 mm (18 in), 600 mm (23.5 in), and 720 mm 

(28.4 in), respectively and the cable tension for the two pickup truck tests averaged 24.5 kN 

(5500 lb). The posts were S-shape posts made from ASTM A36 steel galvanized after 

fabrication. For both tests, the posts were set into tubular steel sockets formed in 305-mm 

(12-in) diameter concrete footings 760-mm (30-in) deep. Test 3-11 was run twice, with 

support post spacings of 2.4 meters (7.9 ft) and the standard 3.2 meters (10.5 ft). The reported 

dynamic deflections for these two tests were 2.7 m (8.9 ft) and 2.6 m (8.5 ft), respectively. 

On April 11, 2006, your representatives, Dr. Richard McGinnis and Mr. Jerry Emerson, met 

with Messrs. Artimovich and Powers of my staff and provided them a copy of a test report 

prepared by the Southwest Research Institute (SwRI) entitled “NCHRP Report 350, Test 3-11 

Full-Scale Crash Evaluation of a 111-Meter TL-3 (3-Rope) Wire Rope Safety Fence (SwRI 

Test Nos. BCR-1).” This report detailed a test conducted by personnel from the SwRI at a 

temporary site in Ardmore, Oklahoma. The test installation was identical to that described 

above, but was only 111-meters (364-feet) long with the cables tensioned to 22.2 kN (5000 lb). 

The purposes of this test were to ascertain the dynamic deflection of a shorter Brifen 

installation and to allow a direct comparison with other designs of comparable lengths. When 

impacted at 24.5 degrees and 97.2 km/h with a 2139-kg pickup truck, the dynamic deflection 

of the 111-meter (364-foot) long installation was reported to be 2.1 meters (7.0 feet). All 

NCHRP Report 350 evaluation criteria for this test were satisfactorily met. 

 
2

Based on the test results summarized above, one can conclude that the dynamic deflection of a 

cable barrier is dependent on several factors, including the specific barrier design (i.e., post 

type, post spacing, cable connection to/at the posts, cable tension, and length of barrier 

between anchorages), impact location, and the size, speed and encroachment angle of any 

impacting vehicle. In general, the closer the post spacing and the shorter the length of an 

installation, the less its dynamic deflection will be, but direct comparisons of dynamic 

deflection between dissimilar cable barrier designs (and lengths) are not particularly valid. As 

I have stated in earlier acceptance letters for cable barriers, the design deflection distance is 

based on a single standard test conducted under carefully controlled conditions. It should not 

be considered an exact distance, but rather as a single point within the range of deflections that 

can be expected under actual field conditions. The current draft update of the NCHRP Report 

350 recommends that a standard length of cable barrier be used for future tests so 

transportation agencies can effectively compare the crash performance of the several different 

systems available for use. The FHWA will actively support this recommendation. 

 

Sincerely yours, 

 

/original signed by George E. Rice, Jr./ 

 ~for~ 

John R. Baxter, P.E. 

 Director, Office of Safety Design 

 Office of Safety