U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

Skip to content
Facebook iconYouTube iconTwitter iconFlickr iconLinkedInInstagram


FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter LS-75

Safety Eligibility Letter LS-75 - Safety

Download Version
PDF [419 KB]

DOT logo
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:

Mr. Dean L. Sicking, Ph.D., P.E.
Director, Midwest Roadside Safety Facility
University of Nebraska – Lincoln
2200 Vine Street
130 Whittier research Center
Lincoln, NE 68583-0583

Dear Mr. Thiemann:

This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of specific Valmont pole and decorative base covers for use on the National Highway System (NHS).

Name of system: Various cast aluminum base covers for lighting and luminaire support posts as described below
Type of system: Valmont Decorative "Clamshell" Covers for Various Lighting Poles and Luminaire Supports
Test Level: NCHRP Report 350 Test Level 3 (Pendulum Testing)
Testing conducted by: Midwest Roadside Safety Facility (MwRSF)
Date of request: December 30, 2010
Request initially acknowledged: January 5, 2011

You requested that we find five (5) decorative base covers used with a range of previously-accepted breakaway couplings and with a range of aluminum poles 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." The specific clamshell bases for which acceptance is requested include the Memphis, Washington, Huntington, Harrisburg, and Osceola designs.

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, Luminaires, and Traffic Signals.

The Valmont clamshell designs/pole configurations described below were tested by the MwRSF and found to meet the required evaluation criteria.

Test Descriptions
A test protocol was developed to test the crashworthiness of two "worst case" combinations of clamshell bases and aluminum poles mounted on breakaway couplings.  The largest clamshell base was tested on a 55-foot (16.8-meter) tall aluminum pole/luminaire arm assembly using TRANSPO Industry's 1.25-inch (32-millimeter) diameter double-neck, pole-safe breakaway couplings.  In addition, the heaviest clamshell base that could fit around an 8-foot (2.4-meter) tall aluminum pole without a top attachment was tested, also utilizing TRANSPO breakaway couplings.  The clamshell bases suffered only minor to moderate damage, and the calculated changes in velocity (ΔVs) for the surrogate vehicle in each test satisfied the 16.4 ft/s (5.0 m/s) limit.  The results for NCHRP Report 350 test designation 3-61 were conservatively estimated using the high-speed test extrapolation equation, and all three tested configurations provided ΔVs below the 16.4 ft/s (5.0 m/s) limit.  Each of the three tests that were conducted is described in more detail below.

In test LST-440, the 1,842-pound (836-kilogram) pendulum impacted an 8-foot (2.4-meter) nominal height aluminum pole fitted with your Memphis decorative clamshell base (Enclosure 1) at a speed of 21.5 mph (34.7 km/h).  In this test, the welds between the pole and the base plate fractured instead of the TRANSPO couplings.  Consequently, the base plate and couplings remained attached to the foundation after the initial impact leaving a stub height of 9⅞ inches (251 millimeters), exceeding the 4-inch (100-millimeter) height limit.  Therefore, this test was repeated as test LST-455 after a sweeper plate was added to the pendulum.  Enclosure 2 is a summary of the test results for LST-440.

In test LST-441, the pendulum impacted a 55-foot (16.8-meter) nominal height aluminum pole and your Washington decorative clamshell base (Enclosure 3) at a speed of 21.8 mph (35.1 km/h).  All four couplings fractured at the lower neck location leaving a stub height of 3 inches (76 millimeter) which falls below the 4-inch (100-millimeter) limit. Enclosure 4 is a summary of these test results.

Test LST-455 was a repeat of test LST-440.  With the addition of the aforementioned sweeper plate to the pendulum, the TRANSPO couplers fractured at their lower necks, leaving a stub height of only 3 inches (76 millimeters).  Enclosure 5 is a summary of test LST-455.

Crash Testing
Pendulum testing was conducted on the test articles described above by the MwRSF at Valmont's pendulum facility in Valley, Nebraska.  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.

Based on the test results described above, your Memphis-15 and Washington-30 clamshell bases are considered to be crashworthy when used in combination with the breakaway couplings and pole sizes in tests LST-440 and LST-441.  Since testing was conducted using both the shortest and lightest pole used with the heaviest base for that pole size and with the largest pole/luminaire and heaviest base combination, you requested acceptance of intermediate pole and clamshell base combinations.  The additional bases were the Huntington (Enclosure 6), the Harrisburg (Enclosure 7), and the Osceola (Enclosure 8) designs. In summary, the FHWA concurs that these five bases are acceptable for use on the NHS when:

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


Page last modified on December 17, 2013
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000