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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-141D

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U.S. Department of Transportation
Federal Highway Administration

1200 New Jersey Ave. S.E.
Washington, D.C. 20590

March 19, 2009

In Reply Refer To: HSSD/B-141D

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 the Federal Highway Administration (FHWA) acceptance of modifications to your CASS cable barrier roadside safety system for use on the National Highway System (NHS).

Name of system: Trinity’s CASS 3-Cable Barrier
Variations: Test Level 4 on 1:6 slopes or flatter, 3 Cables
Test Level 3 on 1:4 slopes, 4 Cables
Test Level 4 on 1:6 slopes or flatter, 4 Cables
Type of system: Three or four cable barrier system
Test Levels: NCHRP Report 350 TL-3 and TL-4
Testing conducted by: Texas Transportation Institute
Date of requests: October 20 and December 11, 2008

You requested that we find these systems acceptable for use on the NHS under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features.”

Requirements
Roadside safety systems should meet the guidelines contained in the NCHRP Report 350. The FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
The FHWA has accepted the CASS 3-cable system to test level 3 (TL-3) criteria in the following FHWA Acceptance Letters:

B-119 (3m / 8 ft post spacing), dated May 13, 2003
B-119A (5m / 16.5 ft post spacing), dated May 13, 2003
B-119B (2m / 6.5 ft post spacing), dated August 28, 2003

The FHWA acceptance letter B-141C Revised (dated November 14, 2008) found the Trinity CASS 3-cable barrier system acceptable for use on a 1:4 slope per NCHRP Report 350 TL-3 conditions. 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.

Your first request is for this TL-3 barrier to be used as a TL-4 barrier on slopes of 1:6 or flatter. This system differs from the previously accepted TL-4 system (see FHWA Acceptance Letter B-157 dated April 23, 2007) only in the heights of the cables and how the bottom cable is attached to the post. As the proposed spread of the three cables is wider than the previously accepted system we concur that these changes should have no adverse affect on the crashworthiness of the barrier system.

Your second request is to add a fourth cable (between the top and middle cables) to the TL-3 barrier accepted in B-141C. Because the addition of the fourth cable at a height of 949 mm (37.375”) above the ground surface, measured to the center of the cable is not considered to be detrimental to the performance of the crash tested system, and is indeed likely to increase the capacity and improve the performance, the CASS system described in Letter B-141C with the added cable is acceptable. It is understood that the added cable will have its own anchorage just like the other cables.

Your third request is to add a fourth cable (between the top and middle cables) to the TL-4 barrier on 1:6 or flatter slopes discussed above. Because the addition of the fourth cable at a height of 949 mm (37.375”) above the ground surface, measured to the center of the cable is not considered to be detrimental to the performance of the crash tested system, and is indeed likely to increase the capacity and improve the performance, this CASS system with the added cable is acceptable. It is understood that the added cable will have its own anchorage just like the other cables.

Finally you requested that these CASS Systems be acceptable with post spacings from 2.0 m (6.5 feet) to 5.0 m (16.5 feet) and with the same range of post embedment types (direct driven, set in driven tube, set in tube sleeve in concrete foundation). These variations have been shown to be crashworthy in earlier testing and will be acceptable for these systems. The end terminal acceptance for these systems was included in acceptance letter B-157, dated April 23, 2007.

CASS System Variations
Date FHWA Letter CASS System Description Cable Heights inches Drawing
November 17, 2005 B-141 3-Cable TL-4 on 1V:6H Slopes 20.9", 30.5", 38.1 SS-740
April 23, 2007 B-157 4-Cable TL-4 on 1V:6H Slopes 20.9", 26.2", 30.5", 38.1" SS-740-740-4
November 14, 2008 B-141C
(Revised)
3-Cable TL-3 on 1V:4H Slopes 17.5", 29.5", 41.7" SS-730-4:1-3C
This letter B-141D 3-Cable TL-4 on 1V:6H Slopes 17.5", 29.5", 41.7" SS-730-4:1-3C
This letter B-141D 4-Cable TL3 on 1V:4H Slopes 17.5", 29.5", 37.4", 41.7" SS-730-4:1-4C
TL4 on 1V:6H Slopes

Findings
The 3- and 4-cable barrier systems described above are acceptable for use on the designated or flatter slopes under NCHRP Report 350 TL-3 or 4 conditions as noted. The systems are detailed in the enclosed drawings and are acceptable for use on the NHS when such use is acceptable to a highway agency.

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

 

Sincerely yours,

David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

Page last modified on August 16, 2011.
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