Refer to: HSA-10/SS-119

Mr. Stuart Cole 

Northwest Pipe Company 

Traffic Systems 

P.O. Box 2002 

Houston, Texas 77252-2002 

Dear Mr. Cole: 

On February 27 an acceptance letter was sent to you, numbered SS-115, which found the 

following systems acceptable for use on the National Highway System: 

1) Northwest Pipe POZ LOC S-Q Post TM Sign Support System 

2) PozLoc Sign Support System with extended anchor for use in weak soils. 

3) PozLoc Breakaway Mailbox Support System for snow regions. 

Please note that we have found it necessary to revise the designation of that letter to 

“SS-119.” 

I apologize for any inconvenience, and I appreciate your understanding. 

 Sincerely yours, 

John R. Baxter, P.E. 

 Director, Office of Safety Design 

 Office of Safety 

FHWA:HSA-10:NArtimovich:tb:x61331:8/12/03 

File: SS119NWpipeFIN.wpd 

cc: HSA-10 (Reader, HSA-1; Chron File, HSA-10; 

 N. Artimovich, HSA-10) 
Refer to HSA-10/SS-115 

Mr. Stuart Cole 

Northwest Pipe Company 

Traffic Systems 

PO Box 2002 

Houston, TX 77252-2002 

Dear Mr. Cole: 

Thank you for your letters of December 27, 2002, January 15, 2003, and February 10, 2003, 

requesting Federal Highway Administration (FHWA) acceptance of variations to your 

company's breakaway support systems for use on the National Highway System (NHS). 

Accompanying your letters were: 1) a report from the Texas Transportation Institute (TTI) on the 

square slipbase system, and videos of the crash tests; 2) a 1996 TTI report on weak soil testing of 

the PozLoc system; and 3) drawings of the PozLoc Breakaway Mailbox Support. You requested 

that we find the following acceptable for use on the NHS under the provisions of National 

Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for 

the Safety Performance Evaluation of Highway Features.” 

1) Northwest Pipe POZ LOC S-Q Post TM Sign Support System 

2) PozLoc Sign Support System with extended anchor for use in weak soils. 

3) PozLoc Breakaway Mailbox Support System for snow regions. 

Introduction 

Testing of the Square Slipbase Sign Support System and prior testing of the PozLoc systems 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' (AASHTO) Standard Specifications for Structural Supports for Highway Signs, 

Luminaires and Traffic Signals. 

1) The Northwest Pipe POZ LOC S-Q Post TM Slipbase Sign Support System consists of a 

2.5 x 2.5 inch x 10 ga and 12 ga perforated square steel tube signpost mounted in a triangular 

slip base system. This system uses a 0.02 inch thick triangular keeper plate separated from the 

base plate by circular cardboard washers. A 3 3⁄4 inch long horizontal 0.5 inch diameter pin 

through the holes in the signpost prevent the end of the post from dropping below the slip joint. 

In test NWP-P1, the lower portion of the slip base was rigidly anchored to the steel anchor plate 

in the pendulum facility. In test NWP-P2, the lower portion of the slip base was mounted in a 

standard TxDOT concrete footing placed in NCHRP Report 350 standard soil at the pendulum 

Facility. Details of the triangular slip base system are detailed in the diagrams that are enclosed 
2

for reference. A 48 x 48 inch x 5/8-inch thick plywood sign panel was mounted at a height of 

7 feet in test P1, and at a height of 7 feet, 2 inches in test P2. The slip base bolts were torqued to 

40 foot-pounds in test P1 and to 60 foot-pounds in test P2 

Testing 

Pendulum testing was conducted on the slip base system. The mass of the test bogie was 820 kg 

in all tests. The test bogie was equipped with a crushable honeycomb nose simulating the front 

end of a Volkswagen Rabbit. (Although no longer produced, this configuration is considered a 

“worst case” design.) The complete devices as tested are shown in the Enclosures. 

Test Number NWP-P1 NWP-P2 

Foundation Type Rigid test foundation Concrete footer in Std soil 

Pendulum Test Mass 

Slip Base Bolt Torque 40 foot pounds 60 foot pounds 

Impact Angle Zero degrees Zero degrees 

Test Impact Velocity 21.1 mph (34 kmh) 21.2 mph (34.2 kmh) 

Occupant Impact Speed None None 

Bogie Delta V 1.32 fps (0.43 m/s) 1.47 fps (0.47 m/s) 

Extrapolated high speed Delta 

V 

1.84 fps (0.56 m/s) 1.73 fps (0.53 m/s) 

Stub Height 4 inches 3-1/2 inches 

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

windshield. Delta V: Speed change of the test vehicle / bogie. 

Findings 

Velocity changes were all within acceptable limits. Because stub heights were at the 4-inch 

maximum we recommend that installation instructions stress the need to keep the height of the 

lower slip plate below the 4 inch maximum as required by the AASHTO Specification. The 

results of testing met the FHWA requirements and, therefore, the Northwest Pipe Square 

Slipbase Sign Support System 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. 

2) PozLoc Sign Support System with extended anchor for use in weak soils. The PozLoc 

sign support system was crash tested in weak soils in February of 1997. In both the low and high 

speed tests the post pulled the socket / anchor out of the ground (in strong soil, the post pulls out 

of the socket.) FHWA Acceptance Letter SS-65A, dated 6-20-97, covered the PozLoc system in 

all soil types. The PozLoc anchor used in the testing was 33 inches (383 mm) long. Your current 

request is to find this system acceptable if anchors 48 inches (1220 mm) or 60 inches (1525 mm) 

long are used. Because of the increased embedment length it can be assumed that there will be 

greater resistance to pullout. After reviewing the prior crash testing we have concluded that the 

greater resistance will not be a disadvantage. If the anchor does not pull out then the system’s 
3

performance will be more like that seen in the strong soil testing. In those tests, the subject of 

FHWA Acceptance Letter SS-1 dated 5-13-86, the vehicle velocity changes were also below the 

“desirable” limits. Therefore, we concur that 48-inch and 60-inch long PozLoc anchors are 

acceptable for use. 

3) PozLoc Breakaway Mailbox Support System for snow regions. The Northwest Pipe Co. 

90 Degree Poz-Loc Socket Assembly for use with mailboxes is similar to the POZ-LOC Socket 

System with a minor difference. The single box cantilevered support system currently being used 

is 1-1/4 inch Schedule 40 pipe fabricated with pipe fittings (drawings enclosed for reference) in a 

concrete base. You proposed that the post be a 2-3/8 inch OD 14 ga pipe using a swaged elbow. 

The post is to be mounted in a POZ-LOC Socket and wedge mounted in concrete. You also 

requested a different single and double box support, which is a simple vertical 2-3/8 inch OD 

14 ga pipe, mounted on a POZ-LOC post and socket. Because the Poz-Loc anchor performance 

has been found acceptable for sign supports, and the thin 14 gage steel is specified for the pipe 

supporting the mailbox, these systems can be expected to perform in an acceptable manner. 

Findings: 

In addition to the square slipbase system discussed as item 1) above, the Poz-Loc supports 

covered as items 2) and 3), as 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, or under the range 

that similar systems were tested, when proposed by a state. 

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

 Our acceptance is limited to the crashworthiness characteristics of the devices and does 

not cover their structural features, or 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. 

 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 FHWA and 

NCHRP Report 350. 

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

SS-115 shall not be reproduced except in full. As this letter and the supporting 

documentation that support it become public information, it will be available for 

inspection at our office by interested parties. 

 Northwest Pipe Company’s Poz-Loc S-Q Post TM slipbase system is a patented product 

and is considered "proprietary." The use of proprietary devices specified on Federal-aid 
4

projects, except exempt, non-NHS projects (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 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, a copy of which is enclosed. 

 Sincerely yours, 

 Michael S. Griffith 

 Acting Director, Office of Safety Design 

 Office of Safety 

2 Enclosures 

 

FHWA:HSA-10:Nartimovich:db:x61331:2/26/03 

cc: Reader – HSA-1, HAS-10(Chron File, NArtimovich) 

h:directoryfolder/nartimovich/ss15nwpipeFIN