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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter LS-74

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U.S. Department of Transportation
Federal Highway Administration

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

September 9, 2011

In Reply Refer To:
HSST/LS-74

Mr. Joseph M. Bowman, P.E.
Director of research and Development
Hapco Aluminum Pole Products
26252 Hillman Highway
Abington, VA 24210

Dear Mr. Bowman:

This letter is in response to your requests for the Federal Highway Administration (FHWA) acceptance of specific Hapco roadside safety systems for use on the National Highway System (NHS).

Name of system: Various breakaway bases and decorative covers for lighting and luminaire support posts as described below
Type of system: Breakaway Hardware/Decorative Covers for Various Lighting Poles and Luminaire Supports
Test Level: NCHRP Report 350 Test Level 3 (Pendulum Testing)
Testing conducted by: Texas Transportation Institute for Hapco
Date of request: December 21 and 28, 2010
Request acknowledged: Request acknowledged:

You requested that we find five (5) breakaway post designs and three (3) decorative base covers used with previously-accepted breakaway post designs 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."

Requirements
Roadside safety devices should meet the guidelines contained in the National Cooperative
Highway Research Program (NCHRP) Report 350 if tested prior to December 31, 2010, and the American Association of State Highway and Transportation Officials' (AASHTO) Manual for Assessing Safety Hardware (MASH) if tested after that date. Requirements for breakaway supports are contained in the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Signals.

Decision

The Hapco designs/configurations shown in the Test Summary below were tested by TTI and found acceptable as indicated.  In four cases, design modifications were made to the hardware initially used in failed tests and the tests were repeated with successful results.

Test Summary

Hapco TTI Breakaway Device Tests October - November 2010

Drawing TTI Test Test Date Results Device
B18836 P15 10/6/2010 Fail 67238A coupling
B18836 P16 10/6/2010 Pass 67238A coupling
B18859 P17 10/6/2010 Pass 67238A coupling
Sample-515 P18 10/7/2010 Fail 18357 casting assembly
Sample-513 P19 10/7/2010 Fail 17642 casting assembly
Sample-514 P20 10/7/2010 Pass 25089 (13172 casting with machined groove)
Sample-512 P21 10/7/2010 Pass Hapco Energy Transfer Profile with 2-pc decorative cover at impact point w/nylon fasteners for use with previously accepted breakaway devices.
Sample-511 P22 10/7/2010 Pass Hapco 2-piece decorative cover below impact point w/nylon fasteners for use with previously accepted breakaway devices.
Sample-510 P23 10/7/2010 Fail Hapco 2-piece decorative cover below impact point w/nylon fasteners for use with previously accepted breakaway devices.
Sample-515 P24 11/23/2010 Pass 25090 (18357 casting assembly modified with machined groove)
Sample-513 P25 11/23/2010 Pass 25088 (17642 casting assembly modified with machined groove)
Sample-510 P26 11/23/2010 Pass Hapco 2-piece decorative cover below impact point w/nylon fasteners for use with previously accepted breakaway devices.
19880 P27 11/23/2010 Pass Hapco Modular t-base assemble using 15190 corner casting
19881 P28 11/23/2010 Pass Hapco Modular t-base assemble using 15190 corner casting

Test Descriptions
TTI Tests P15, 16, and 17:  These tests were run using HAPCO's modified breakaway coupling 67238A (Enclosure 1).  Test P15 was not successful because the post did not breakaway and the occupant impact velocity was 10.5 m/s, well over the allowable maximum of 5 m/s. It was determined the failure was caused by improper installation.  Specifically, there was no gap left between the breakaway couplings and the foundation/support base.  This deficiency was corrected and drawings B18836 and B18859 (Enclosures 1A and 1B) were revised to show the required gap.  Test P16, using a tapered aluminum pole with a 55-foot mounting height, resulted in an occupant impact velocity of 3.3 m/s.  Test P17, using a tapered aluminum pole with a 50-foot mounting height, resulted in an occupant impact velocity of 3.2 m/s.  The calculated high speed changes in velocity were reported to be 3.6 m/s and 2.4 m/s for Tests P16 and P17, respectively.

TTI Tests P18 and 24: Test P18 was run using HAPCO's Decorative Pedestal (18357) to support its Sample-515 lighting pole.  This test produced an occupant impact velocity of 5.4 m/s, slightly above the maximum value allowed.  The Pedestal was modified by drilling two 6 millimeters (0.25-inch) holes19 millimeters (0.75 inches) above the base and 146 millimeters (5.75 inches) apart.  These holes were connected by a 3 millimeters (0.125 inch) slot to create a shear plan when the base is impacted by a vehicle.  The modified design is designated as part 25090 and is shown as Enclosure 2. Test P24 was a test of the modified design with the tapered aluminum tube shown in Enclosure 2A.  The low-speed occupant impact velocity was reported to be 3.6 m/s and the calculated high-speed OIV was reported to be 2.4 m/s.

TTI Tests P19 and 25: Test P19 was run using HAPCO's Decorative Pedestal (17642) to support its Sample-513 lighting pole.  This test resulted in an unacceptable low-speed OIV of 5.9 m/s. The Pedestal was modified by drilling two 6 millimeters (0.25-inch) holes 22 millimeters (0.875 inches) above the base and 152 millimeters (6 inches) apart.  These holes were connected by a 3 millimeters (0.125 inch) slot to create a shear plan when the base is impacted by a vehicle.  The modified design is designated as part 25088 and is shown as Enclosure 3. Test P25 was a test of the modified design with the tapered aluminum tube shown in Enclosure 3A.  The low-speed occupant impact velocity was reported to be 5.0 m/s and the calculated high-speed OIV was reported to be 2.6 m/s.

TTI Test P20: Test P20 was run on HAPCO's Sample-514 lighting pole supported by a Decorative Pedestal made from 356-T6 aluminum and modified from the previously-accepted part 13172 to add a machined groove.  The modified design, part 25089, is shown as Enclosure 4 and the tested set-up is Enclosure 4A.  Upon impact with the pendulum, the pole separated from the base.  Although this separation is not desirable, the test video showed that the sheared pole continued to move away from the impact point and thus was not likely to impact the windshield of a vehicle in an actual crash. The reported OIV was 3.1 m/s and the calculated high-speed value was 3.1 m/s

TTI Test P21: This test was conducted to verify acceptable crash performance of a decorative base cover installed over a previously-accepted breakaway design.  This cover is a two-piece cast aluminum design bolted together with 10-millimeters (0.375 inch) nylon hex screws and nuts to ensure separation of the two halves in a crash.  The reported low-speed OIV was 2.9 m/s and the calculated high-speed value was 1.4 m/s.  The tested set-up with pole Sample-512 is shown in Enclosure 5.

TTI Test P22: This test was also conducted to verify acceptable crash performance of a decorative base cover installed over a previously-accepted breakaway design.  This cover is a two-piece cast aluminum design bolted together with 10-millimeters (0.375 inch) nylon hex screws and nuts to ensure separation of the two halves in a crash. The reported low-speed OIV was 3.3 m/s and the calculated high-speed value was 1.8 m/s.  The tested set-up with pole Sample-511 is shown in Enclosure 6.

TTI Tests P23and 26: Test P23 was conducted to verify acceptable crash performance of a decorative base cover installed over a previously-accepted breakaway design.  This cover was also a two-piece aluminum design bolted together with 10-millimeters (0.375 inch) nylon hex screws and nuts to ensure separation of the two halves in a crash.  The test failed with a reported low-speed OIV of 6.0 m/s. Post-impact analysis indicated that the previously-accepted breakaway base failed to yield as designed because of an oversized fillet weld.  This error was corrected and the system was re-tested under test P26.  In the second test, the reported low-speed OIV was 2.9 m/s and the calculated high-speed value was 1.7 m/s.  The tested set-up with pole Sample-510 is shown in Enclosure 7. Note #3 was added to this drawing to address the aforementioned weld problem.

TTI Tests P27 and 28: Both of these tests used HAPCO's Modular T-base Assembly as shown in Enclosures 8 and 8A.  Test P27 used a 55-foot luminaire mounting height as shown in Enclosure 8B and Test P28 shown in Enclosure 8C used a similar set-up, but with a 50-foot mounting height.  For Test P27, the low-speed actual and high-speed calculated OIV values were 4.5 m/s and 4.4 m/s, respectively.  For Test P28, these values were 4.8 m/s and 3.3 m/s, respectively. Although both test installations used a 14.5-inch bolt circle, you requested the Modular T-base be accepted for use with bolt circles from 10 inches to 17.5 inches.  For a traditional cast aluminum transformer base, FHWA acceptance is limited to the largest diameter bolt circle that was actually tested.  However, in your design, each "leg" of the breakaway structure functions independently of the remaining three.  Therefore, a bolt "circle" ranging from 10 inches to 17.5 inches is acceptable.

Crash Testing
Pendulum testing was conducted on the test articles described above by the Texas Transportation Institute (TTI) at their outdoor pendulum testing facility.  All tests were conducted according to NCHRP 350 test designation 3-60.  The FHWA accepts pendulum tests as surrogates for this low-speed small car test.  The FHWA also allows the results of the high speed tests to be estimated using data from the low-speed pendulum test in combination with an analytical extrapolation method described in the FHWA memorandum "Identifying Acceptable Highway Safety Features" dated on July 25, 1997.

Findings

For all eight test articles, the low speed test results and the high speed test extrapolation analysis resulted in change in velocity values less than the upper limit of 5.0 m/s.

It should be noted that the pole, luminaire arm, and clamshell base covers must meet the conditions and limitations of TRANSPO Industries breakaway couplings identified in FHWA acceptance letter LS-45B particularly the followings:

Therefore, the 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 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 September 27, 2013.
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