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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-88G

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U.S. Department of Transportation
Federal Highway Administration

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

August 18, 2011

In Reply Refer To:
HSST/B-88G

Mr. Jesper Sorensen
Safence, Inc.
1557 N.W. Ballard Way
Seattle, WA 98107

Dear Mr. Sorensen:

This letter is in response to your request for the Federal Highway Administration (FHWA) to review a roadside safety system for eligibility for reimbursement under the Federal-aid highway program.

 

Name of system:

SAFENCE Cable Barrier on 1V:4H Slopes

Type of system:

Modified Cable Barrier (post design)

Test Level:

NCHPR Report 350 TL-3

Testing conducted by:

Midwest Roadside safety Facility (MwRSF)

Date of request: December 28, 2010
Date of completed package: December 30, 2010
Task Force 13 Designator: SGM32

You requested that we find this modified system acceptable for use on the NHS as a TL-3 barrier under the provisions of NCHRP Report 350.

Requirements
Roadside safety systems should meet the guidelines contained in National Cooperative Highway Research Program (NCHRP) Report 350 if tested prior to January 1, 2011, and the guidelines contained in AASHTO's Manual for Assessing Safety Hardware (MASH) if tested after that date.  The FHWA Memorandum "ACTION: Identifying Acceptable Highway Safety Features" of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Decision
The following system was found acceptable, with details provided below:

Description
Various designs of the Blue System/Safence have been previously tested and accepted under the following the FHWA Acceptance Letters:

FHWA Acceptance
Letter Number
Date Test
Level
System
Types
B-88 July 13, 2001 TL-3 Roadside Driven elliptical posts
B-88A January 28, 2004 TL-3 3504RI Median Driven I posts
B-88B June 08, 2004 TL-3 Concrete footers
B-88C May 26, 2005 TL-3 Roadside Allow "C" posts
B-88D December 27, 2006 TL-4 3RC Modified "C" posts
B-88E July 31, 2007 TL-4 Add fourth Cable to TL-4 Safence
B-88F December 23, 2008 TL-3
(MASH)
3 and 4-cable Safence on 1V:4H slope

 The tested metric cable heights for these systems are as follows:

FHWA Acceptance
Letter Number
As tested metric cable heights
(millimeters)
B-88 480 630 780 930
B-88A 480 560 640 720
B-88B 480 560 640 720
B-88C 480 630 780 930
B-88D 480 640 720 -
B-88E 480 560 640 720
B-88F 500 785 880 975

(Tested with 3 cables – 4th cable optional)

Your current request is the acceptance of a modified version of the 3-cable (and 4-cable) Safence placed 4 feet (1.22 meters) beyond the hinge point of a 1V:4H fill slope.  This modification consisted of strengthening the original "C" posts to reduce the dynamic deflection of the barrier system.  The posts are made from ASTM A1011-04a high-strength, low alloy Grade 50 steel. Each post is 1480 millimeters (58.3 inches) long, 95 millimeters (3.74 inches) wide, 30 millimeters (1.189 inches) deep, and 4.1 millimeters (0.16-inch) thick.  The posts were strengthened by the addition of steel post stiffeners measuring 84 millimeters (3.3 inches) wide x 900 millimeters (35.4 inches) long x 5 millimeters (0.2-inch) thick.  The posts were set 457 millimeters (18 inches) in plastic sleeves embedded in a continuous concrete footing.  For the test conducted, the posts were spaced 4.9 meters (16 feet) apart.  The total installation length was approximately 304 feet (92.7 meters).  This length was selected for comparison to other cable systems tested on 1V:4H slopes.  Your original slope test, using the MASH pickup truck (B-88F), was conducted on an installation that was 185 meters (607 feet) long with 2100 millimeters (82.7 inches) long posts directly embedded 1050 millimeters (41.3 inches) in a "standard soil". In that test, the design deflection distance was 5 meters (16.4 feet).

The 19 millimeters (¾-inch) diameter cables were installed at heights of 490 millimeters (19.3 inches) , 785 millimeters (30.9 inches), and 975 millimeters (38.4 inches) above the ground and tensioned to approximately 5,600 pounds (24.9 km) prior to the test.  Details of this system are included as enclosure to this correspondence.

Crash Testing
NCHRP Report 350 test 3-11 was conducted on November 2, 2010. A 1990 Chevrolet C2500 impacted the Safence barrier at 101.7 km/hr (63.2 mph) and at a 25 degree impact angle.  The vehicle was redirected by the barrier and stopped after traveling about 77 meters (250 feet).  As seen in the test summary sheet (Enclosure 3), all evaluation criteria were met.  The observed deflection distance under the test conditions was 9.2 feet (2.8 meters).  Because one post was inadvertently omitted from the test installation, a post-crash analysis concluded that the deflection would have been slightly less (8.5 feet/2.6 meters) had the post been in place.  The FHWA has long contended that minor differences in the reported design deflections of cable barrier systems are relatively inconsequential, considering the large range of impact conditions likely to be found in the field.  Crash test summary is included as enclosure to this correspondence.

Findings
The vehicle trajectories and occupant risk values were within the evaluation criteria contained in NCHRP Report 350.  You also requested that a 4-cable design also be considered acceptable under similar median conditions, with the 4th cable placed between the middle and top cables at an approximate height of 870 millimeters (34.3 inches).  We agree that the addition of a fourth cable would not be detrimental to system performance, but would actually serve to reduce the design deflection below that seen in the test described above as well as improve the overall capacity of the system.  However, without an actual test of the single-unit truck on the 1V:4H slope, the FHWA is not willing to classify the 4-cable design used on a 1V:4H slope at NCHRP Report 350 TL-4.

Therefore, the system described above and detailed in the enclosed drawings is acceptable for use on the NHS as an NCHRP Report 350 TL-3 barrier.

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

 

Sincerely yours,

/* Signature of Michael S. Griffith */

Michael S. Griffith
Director, Office of Safety Technologies
Office of Safety

Enclosures

Page last modified on June 24, 2011.
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