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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-120

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

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U.S. Department of Transportation
Federal Highway Administration

September 7, 2011

Reply Refer To:

Mr. Dallas James
Armorflex International Ltd.
8 Paul Matthews Road,
North Harbour 0751
New Zealand

Dear Mr. Dyke:

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: X-LITE Terminal
Type of system: Tangent & Flared Re-directive Gating W-Beam Terminal
Test Level: NCHRP Report 350 TL-3
Testing conducted by: Safe Technologies, Inc.
Date of request: December 20, 2010
Request acknowledged: December 27, 2010
Task Force 13 Designator: SEW23 Tangent
SEW24 Flared

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

Roadside safety devices tested prior to January 1, 2011 should meet the guidelines contained in NCHRP Report 350; those tested after that date must follow the guidelines contained in the American Association of State Highway and Transportation Officials' (AASHTO) Manual for Assessing Safety Hardware (MASH). The FHWA Memorandum Identifying Acceptable Highway Safety Features" of July 25, 1997 provides further guidance on crash testing requirements for longitudinal barriers.

The following barrier design was found acceptable, with details provided below:

he X-LITE Terminal evolved from the original X-Tension Terminal (FHWA letter CC-91) and incorporates many of the key components and design features of the X-Tension. Like the earlier design, the X-LITE Terminal absorbs the kinetic energy of the impacting vehicle when struck head on by telescoping the W beam panels, gathering and retaining the rails into the slider mechanism. The friction applied by the slider mechanism increases with each additional rail that it gathers and retains, thereby gradually increasing the energy absorbing capability of the X-LITE Terminal. When hit at an angle at or beyond the third post, the X-LITE Terminal is restrained laterally by the W-Beam panels and its end anchor. This anchor consists of posts #1 and #2 connected by tension struts and a soil plate below grade on post #2.

The X-LITE Terminal consists of 3 standard W-beam panels installed on I-beam posts. using either composite or routed wood offset blocks. It can be installed parallel to the roadway or flared with a 1220-millimeter (48-inch) offset over 11.4 meters (37.5 feet), there are 6 modified (crimped) posts used in the flared design and 3 in the tangent design, including post #2 in both designs. The flared design includes an offset block at post #2, whereas the tangent design does not. For both layouts, only the offset block is bolted to post #5. Based on the test results reported below, the X-LITE can be installed with the top of the rail at either 702 millimeters (27 5/8 inches) or 787 millimeters (31 inches) above grade. The slider mechanism is at the joint between rails I and 2, with shear bolts at the joint between rail 2 and 3. An additional set of shear bolts between rails 3 and 4 are used in the tangent system only.

Enclosures I and 2 show the design and assembly of the flared and tangent X-LITE Terminal systems respectively. .

Crash Testing
The crash test matrix was developed in consultation with the FHWA's Office of Safety Design and the following tests were conducted to validate the crashworthiness of the X-LITE Terminal: NCHRP Report 350 test designations 3-31 and 3-35 were conducted on the flared system at 27 5/8 inches high and test 3-30 was run using a rail height of 31 inches; tests 3-31 and 3-30 were also run on the tangent system. To provide additional support of the X-LITE at 31 inches high, test 3-34 was run on the X-Tension Terminal. Each of these tests is briefly described below.

Flared design:
Test 3-30 was conducted with the rail height set at 787 millimeters (31 inches) to verify that the 820C vehicle would not underride the impact head. Enclosure 3 is the summary sheet for this test.

Test 3-31 was conducted with the rail height set at 702 millimeters (27 5/8 inches) to verify impact performance with the 2000P test vehicle. The pickup truck proceeded through the terminal and came to rest behind the test installation. 27 meters (approximately 90 feet) downstream from the impact point. While this trajectory is common to all Oared. gating W-beam terminals, it serves to emphasize the importance of a clear and traversable runout area behind and beyond such terminals. Enclosure 4 is the summary sheet for this test.

Test 3-34 with the 820C vehicle impacting the side of the system at the critical impact point (CIP) at a 15-degree angle was conducted using the flared X-Tension design at the 787-millimeter (31-inch) height. Since the X-Tension has only two weakened posts at the front, followed by standard steel line posts, this test was considered to be a more severe test of wheel snag than the X-LITE with its six crimped posts. Enclosure 5 is the summary sheet for this test.

Test 3-35 was conducted with the 2000P vehicle impacting the side of the terminal at post #3 at a nominal angle of 20 degrees. Because of the flared terminal layout, the actual impact angle was approximately 26 degrees. For this test, the lower rail height of 702 millimeters (27 5/8 inches) was used. The pickup truck was contained and redirected, thus confirming the barrier length of need (LON) begins at post #3. Enclosure 6 is a summary of the test conditions and results.

In your request, you noted that tests 3-32 and 3-34 were not run because these tests have always been shown to be less severe than the end-on tests for gating terminals. Test 3-39, a reverse-direction, 20 degree test with the pickup truck was not run on the flared X-LITE design based on the successful performance of the tangent X-Tension test which you conducted during certification testing for that design. The flared X-LITE layout reduces the effective impact angle to approximately 14 degrees so the impact would be less severe than the earlier test. The FHW A reconfirms that these three tests can be waived.

Tangent design:
Test 3-30 was run on the X-LITE tangent design which uses only three modified (crimped) posts. For this test, the 820C vehicle was offset the field side of the terminal to maximize the likelihood of the car yawing into the standard steel posts beginning with post #4. The rail height was set at 702 millimeters (27 5/8 inches). Although all Report 350 test criteria were met, the car travelled over 20 meters (66 feet) behind the rail from the initial impact point and exhibited a roll angle slightly over 50 degrees. This post-impact trajectory again reinforces the need for a relatively clear and traversable runout area behind and beyond all gating terminals. Enclosure 7 is a summary of these test results.

Test 3-31 was run with the rail set at its lower limit of 702 millimeters (27 5/8 inches) to verify its capability to stop the 2000P vehicle without override. Enclosure 8 is a summary of this successful test.

Tests 3-32 and 3-33 were not run on the tangent layout for the same reason they were waived for the flared design. Test 3-34 and 3-35 were not run on the tangent system because these tests were successfully completed on the more-critical flared design and would be less severe on the tangent system. Test 3-39, as noted earlier, was successfully run on the stiffer X-Tension design during earlier testing. The FHWA agrees that these five tests can be waived for the tangent X-LITE.

Finally, your December 201h request summarized the design changes made to the X-LITE terminal after your initial test 3-35 that were incorporated into the final design. The FHWA concurs that these modifications will not adversely affect the crash test performance of the first test and it need not be repeated.

You requested FHWA acceptance of the following configurations for the X-LITE Terminal as an NCHRP Report 350 TL-3 Re directive, Gating, W-Beam Terminal:

– X-LITE Flared Terminal with a 1220-millimeter (48-inch) offset over 11.4 meters (37.5 feet) at both 702-millimeter (27 5/8-inch) and 787-milimeter (31-inch) rail heights, using either composite or timber offset blocks.

– X-LITE Tangent Terminal with a 0 to 300-millimeter (0 to I-foot) offset at both 702-millimeter (27 5/8-inch) and 787-milimeter (31-inch) rail heights, using either composite or timber offset blocks.

Both systems described above and detailed in the enclosed drawings are acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to a highway agency.

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

This letter includes an AASHTO/ARTBA/AGC Task Force 13 designation that should be used when drafting new or revised Task Force 13 drawings.


Sincerely yours,

Signature of Michael S. Griffith

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


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