1200 New Jersey Avenue, SE. 

Washington, DC 20590 November 14, 2008 

In Reply Refer To: HSSD/B-141C (REVISED)

Mr. Brian Smith 

Trinity Highway Products, LLC 

P.O. Box 568887 

Dallas, TX 75356-8887 

Dear Mr. Smith: 

This letter is in response to your request for Federal Highway Administration (FHWA) 

acceptance of a roadside safety system for use on the National Highway System (NHS). 

 Name of system: CASS cable barrier system on a 4:1 slope 

 Type of system: Three cable median barrier 

Test Level: National Cooperative Highway Research Program (NCHRP) Report 350 

 Testing conducted by: Texas Transportation Institute (TTI) 

 Dates of request: November 28, 2007 and February 5, 2008, 

 Date of completed package: June 22, 2008 

 Letter revised: October, 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.” 

Introduction 

The FHWA guidance on crash testing of roadside safety hardware is contained in a 

memorandum dated July 25, 1997, titled “INFORMATION: Identifying Acceptable Highway 

Safety Features.” 

1. The CASS 4:1 is a tensioned, three-cable barrier system that was tested with standard 

(non-prestretched) cables. The middle and top cables are positioned within a 

wave-shaped slot in the web of S100 x 11.5 (S4 x 7.7#) structural I-beam posts. The 

bottom cable is supported on the median-side flange of the I-beam post by an 8 mm 

(5/16 inch) hook bolt with the open end down. The proprietary S100 x 11.5 (S4 x 7.7#) 

posts have weakening holes at the ground line and were installed in steel tube sleeves set 

in 305 mm (12 inch) diameter x 762 mm (30 inch) deep concrete footings. Post spacing 

was 6.1 m (20 feet) for the first three tests and 2.03 m (6 feet 8 inches) for the fourth test. 

The cables within the wave-shaped slot are separated by plastic spacers. A stainless steel 

strap is mounted on the outside of the post above the top cable. 
2

The 19 mm (3/4-inch) diameter standard cables were set at heights of 445 mm, 745 mm, and 

1060 mm (17.5, 29.3, and 41.7 inches) above the ground surface, measured to the center of each 

cable. Tension of the cables was set at 24.9 kN (5600 pounds force) for the tests. 

Testing 

Three tests were conducted on the CASS 4:1 system with 6.1m (20 feet 0 inch) post spacing 

installed in a 9.1 m (30 foot) wide depressed median with 1V:4H side slopes. A fourth test was 

conducted on the CASS 4:1 system with 2.03 m (6 feet 8 inch) post spacing. The barrier 

installations and tests intended to show that the system would perform properly when located 

1.22 m (4 feet) from the hinge point and 3.5 m (11 feet) from the ditch invert. The test data 

summary sheets are attached, and the tests are briefly described as follows: 

1. The NCHRP Report 350 Test 3-11 (modified) – 2270P (MASH-08 pickup truck) at 100 km/hr 

with a 25 degree impact angle. The barrier was installed 1.22 m (4 feet) from the break point. 

2. The NCHRP Report 350 Test 3-10 – 820C at 100 km/hr with a 20 degree impact angle with 

the barrier installed 1.22 m (4 feet) from the break point. 

3. The NCHRP Report 350 Test 3-10 – 820C at 100 km/hr with a 20 degree impact angle with 

the barrier installed on the median backslope 3.35 m (11 feet) from the median bottom. The test 

vehicle traveled across the median bottom and traveled up the backslope before impacting the 

barrier. 

4. The NCHRP Report 350 Test 3-11 (modified) – 2270P (MASH-08 pickup truck) at 100 km/hr 

with a 25 degree impact angle. The barrier was installed 1.22 m (4 feet) from the break point. 

Post spacing was 2.03 m (6 foot 8 inch) post spacing. 

Each 100.6 m (330 foot long) test installation was anchored by TTI Breakaway Cable Anchor 

Terminals. Dynamic deflection in Test 3-11 (modified) with 6.1 m (20 foot) spacing was 2.85 m 

(9.35 feet.) Dynamic deflection in Test 3-11 (modified) with 2.03 m (6 foot 8 inch) spacing was 

2.19 m (7.19 feet.) 

You initially requested the FHWA Acceptance under the MASH-08 as you used the appropriate 

quad-cab pickup truck. Subsequently you agreed with the FHWA that the 300-foot length of the 

test article was inadequate under the MASH-08 guidelines, but that the 2270P vehicle would be 

considered acceptable for judging performance under the NCHRP Report 350 in this matrix. 

Findings 

The occupant risk values and vehicle trajectories in all four tests met the appropriate evaluation 

criteria. None of the tests showed potential for vehicle override, penetration, or rollover. 

Therefore, the system placed on a 1V:4H or flatter median slope described above and detailed in 

the enclosed drawings is acceptable for use on the NHS under the range of conditions tested, 

when the barrier’s use is approved by a highway agency under both the NCHRP Report 350. 

Although testing was conducted on standard cables, we concur with your additional request that 

the system be found acceptable with pre-stretched cables.
3

Although the barrier performed well under ideal test impact conditions when originally crash 

tested, the likelihood of passenger car underrides of any cable system may increase as the post 

spacing increases, particularly when the barrier is installed on non-level or slightly irregular 

terrain and the cables are not restrained from lifting at each post. Consequently, some 

transportation agencies have limited post spacing to approximately 6 m (20 feet) for cable 

barriers. The dynamic deflection of the barrier is likely to increase when it is installed along the 

convex sides of horizontal curves, and when distances between anchorages exceed the 350 foot 

test length. 

Sincerely yours, 

David A. Nicol, P.E. 

Director, Office of Safety Design 

Office of Safety 

Enclosures 

FHWA:HSSD:NArtimovich:tb:x61331:2/25/08 

REVISED 11/14/08 

File: s://directory folder/nartimovich/B141Ccass4to1 Draft BS 080220.doc 

cc: HSSD (Reader, HSA; Chron File, HSSD; N.Artimovich, HSSD; 

 MBloschock, HSSD; M.McDonough, HSSD)