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July 28, 1998

Refer to HNG-14/SS-80

Ms. Dottie Aberle
Post Exchanger
1365 Harlan
Lakewood, Colorado 80214

Dear Ms. Aberle:

This is in response to your May 6 letter requesting Federal Highway Administration's (FHWA) acceptance of your company's "Post Exchanger" as a foundation system for small breakaway signs. Accompanying your letter were copies of the crash test report prepared by the Texas Transportation Institute, drawings and material specifications of the Post Exchanger, a video tape of the crash tests, and installation instructions, etc.

Crash testing in accord with National Cooperative Highway Research Program Report 350, "Recommended Procedure for the Safety Performance Evaluation of Highway Features," was conducted to assess the breakaway performance of this small sign support foundation when mounted in concrete footings in "standard" soil. The frontal crush of the 820-kg pendulum bogie's aluminum honeycomb nose simulates the crush of an actual vehicle. Requirements for breakaway supports are those found in the American Association of State Highway and Transportation Officials' (AASHTO) Standard Specifications for Structural Supports for Highway Signs, Luminaries and Traffic Signals.

The USAberle Post Exchanger is a cast-aluminum alloy tube 584-mm long which, when mounted in concrete, provides the base for a sign post (see enclosed drawing). The top of the Post Exchange has adjustable clips in two different sizes with which to stabilize the signpost.

Two different mounting configurations were tested. In tests 400001-USA P and 400001-USA P2, a 100x100x3 mm steel tube 712 mm long was attached at the lower end of the Post Exchanger. This steel tube allowed the extension of the post exchanger approximately 200 to 250 mm into the "standard" soil below the 450-mm diameter concrete footing. This configuration is referred to as the "extended" post exchanger. It was tested with a 100 mm by 100 mm rectangular timber sign post with no holes and with a 10 gauge, 64 mm perforated square steel tube sign post.

In tests 400001-USA P3 and 400001-USA P4, no extension was used, but the 450-mm diameter concrete footing was supplemented with a 1.2m(squared), 127-mm thick concrete pad around the mounting area. This configuration is referred to as the "unextended" post exchanger. It was tested with the standard 100 mm square timber signpost with no holes and standard 50 mm diameter 10-gauge steel round signpost. For all tests, as 760-mm square, 19-mm thick wooden sign panel was mounted on the posts at a height of 2000 mm above the ground level.

Test Number





Post Type*


Square Tube


Round Pipe

Depth Embedded

705 mm

705 mm

577 mm

577 mm

Impact Speed

35.73 km/h

35.51 km/h

35.42 km/h

35.44 km/h

Occupant Impact


3.53 m/s



Velocity Change

0.59 m/s

3.46 m/s

0.43 m/s

8.9 m/s

Stub Height


< 100 mm

7 mm

? mm






*Wood posts were "4x4" posts with no holes. Square tube was 64-mm square perforated 10 gauge steel post. Round pipe was 50 mm diameter 10-gauge steel.

**Wood remains of approximately 100 to 150-mm height remained but were not substantial.

***The pipe was pulled out of the foundation, bent, and halted the bogie.

The USAberle Post Exchanger supporting single 100-mm square wood sign posts or 64-mm perforated square steel tubes (both 10-gauge steel) are acceptable for use on the National Highway System, (NHS) in the range of conditions shown above, when proposed by a State. The round pipe was pulled out of the ground and formed a bend that was snagged by the pendulum, causing the pendulum to stop. It is, therefore, unacceptable for use with the Post Exchanger.

Our acceptance is limited to the breakaway characteristics of the tested and passing supports when used with the USAberle Post Exchanger system and does not cover their structural features. Presumably, you will supply potential users with sufficient information on design and installation requirements to ensure proper performance. We anticipate that the States will require certification from USAberle the hardware furnished has essentially the same chemistry, mechanical properties, and geometry as that submitted for acceptance, and that the foundations will provide rigid support to the sign posts.

If the USAberle Post Exchanger system becomes a patented product, it will be considered "proprietary." The use of proprietary devices specified on Federal-aid projects, except exempt, non-NHS projects: (a) must be supplied through completive bidding with equally suitable unpatented items; (b) the highway agency must certify that they are essential for synchronization with existing highway facilities for 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,

Dwight A. Horne
Chief, Federal-Aid and Design Division


Geometric and Safety Design Acceptance Letter Number SS-80

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