1200 New Jersey Ave., S.E. 

Washington, DC 20590

September 5, 2008 

In Reply Refer To: 

HSSD/SS-128 Revised 

Mr. Raymond Kisiel 

Northwest Pipe Company 

6307 Toledo Street 

P.O. Box 2002 

Houston, TX 77252-2002 

Dear Mr. Kisiel: 

Thank you for your letter of May 9, 2007, requesting an update to your Federal Highway 

Administration (FHWA) acceptance letter of your company’s Poz Loc Slip base Casting 28339 

as a breakaway feature for sign supports for use on the National Highway System (NHS). The 

update of this letter includes changing the reference from casting 2709 to casting 28339 and an 

updated drawing that is enclosed. Slight design modifications have been made which include 

adding a fourth set screw. These modifications will not affect the breakaway performance of this 

device. 

Accompanying your original request letter that was received July 14, 2004, was a report from 

Texas Transportation Institute (TTI) and videos of the crash tests. You requested that we find 

this slip base 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.” You provided additional information on 

February 14 and February 22, 2007 in response to our requests. 

Introduction 

Testing of the supports was in compliance with the guidelines contained in the NCHRP Report 

350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. 

Requirements for breakaway supports are those in the American Association of State Highway 

and Transportation Officials’ Standard Specifications for Structural Supports for Highway Signs, 

Luminaires and Traffic Signals. 

The test article consisted of a 73 mm (2.875 inch) outside diameter schedule 10 pipe support 

with a crossbar at the top, and a 1200 x 1200 mm x 16 mm (48 x 48 x 5/8 inch) plywood sign 

panel attached. The cast iron slip base device weighs 5 kg (11 pounds), the pipe was 4.6 kg 

(10 pounds, 4 oz.), and the sign panel was 14.8 kg (32 pounds, 8 oz.) 
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Testing 

Pendulum bogie testing was conducted on your company’s devices. The mass of the test vehicle 

was 820 kg in all tests. The complete devices as tested are shown in the Enclosures. 

Test # NCHRP 350 Speed Impact Height Occup. Speed Delta V 

1 3-60 35.1 km/hr 18 inches None 0.47 m/s 

2 3-60 35.1 km/hr 24 inches None 0.47 m/s 

Occup. Speed: Occupant Impact Speed: Speed at which a theoretical front seat occupant 

will contact the windshield. In meters per second. 

Delta V: Speed change of the test vehicle. In meters per second. 

Test #1 was conducted at the typical 18-inch bumper height for small cars (and pendulum bogie 

noses.) Test #2 was conducted at 24 inches above the ground to investigate a concern of the 

Texas Department of Transportation regarding the bending of thinner wall tubes. They surmised 

that low speed impacts with taller vehicles, especially in the light truck class, could cause a 

bending failure prior to slip activation. The slip base performed as intended at both heights. 

Calculations based on the FHWA memorandum of November 12, 1993, performed by the TTI 

show the expected velocity change during a 100-km/hr impact to be 0.48 m/s. 

Findings 

The results of the low-speed bogie testing and the high speed extrapolations met the FHWA 

requirements and, therefore, the devices described above and shown in the enclosed drawings for 

reference are acceptable for use as test level 3 devices on the NHS under the range of conditions 

tested, when proposed by a State. 

FHWA accepts the results of testing conducted on torque values for slip base systems performed 

by TTI in 2001 that revealed the torque values for the keeper bolts may be increased from 38 

foot-lbs. to 80 foot-lbs. The use of these increased torque values for keeper bolts is acceptable 

with the Poz-Loc 10 inch round slip base systems and this modification also applies to FHWA 

Acceptance letter SS-65. 

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

• This acceptance is limited to the crashworthiness characteristics of the devices and does not 

cover their structural features, nor conformity with the Manual on Uniform Traffic Control 

Devices. 

• Any changes that may adversely influence the crashworthiness of the device will require a 

new acceptance letter. 

• Should the FHWA discover that the qualification testing was flawed, that in-service 

performance reveals unacceptable safety problems, or that the device being marketed is 

significantly different from the version that was crash tested, it reserves the right to modify or 

revoke its acceptance. 
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• You will be expected to supply potential users with sufficient information on design and 

installation requirements to ensure proper performance. 

• You will be expected to certify to potential users that the hardware furnished has essentially 

the same chemistry, mechanical properties, and geometry as that submitted for acceptance, 

and that they will meet the crashworthiness requirements of the FHWA and the NCHRP 

Report 350. 

• To prevent misunderstanding by others, this letter of acceptance, designated as number 

SS-128, shall not be reproduced except in full. This letter, and the test documentation upon 

which this letter is based, is public information. All such letters and documentation may be 

reviewed at our office upon request. 

• The device is a patented product and considered proprietary. If proprietary devices are 

specified by a highway agency for use on Federal-aid projects, except exempt, non-NHS 

projects, they: (a) must be supplied through competitive bidding with equally suitable 

unpatented items; (b) the highway agency must certify that they are essential for 

synchronization with the existing highway facilities or that no equally suitable alternative 

exists; or (c) they must be used for research or for a distinctive type of construction on 

relatively short sections of road for experimental purposes. Our regulations concerning 

proprietary products are contained in Title 23, Code of Federal Regulations, Section 635.411. 

• This acceptance letter shall not be construed as authorization or consent by the FHWA to use, 

manufacture, or sell any patented device for which the applicant is not the patent holder. The 

acceptance letter is limited to the crashworthiness characteristics of the candidate device, and 

the FHWA is neither prepared nor required to become involved in issues concerning patent 

law. Patent issues, if any, are to be resolved by the applicant. 

Sincerely yours, 

 

 George E. Rice, Jr. 

 Acting Director, Office of Safety Design 

 Office of Safety