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July 26, 1999

Refer to: HMHS / SS-84

Mr. Francisco D. Estrada, Supervisor
Los Angeles County SAFE
One Gateway Plaza
Los Angeles, California 90012-2932

Dear Mr. Estrada:

Thank you for your February 25 letter to the Director, Office of Engineering, requesting acceptance of the Comarco Wireless Technologies' TTY Call Box support system as a breakaway support for use on the National Highway System. Accompanying your letter was a report of crash testing done at E-Tech Testing Services dated December 1998, and videos of the crash tests.

Testing of the supports was in compliance with the guidelines contained in the National Cooperative Highway Research Program (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


The test articles each consisted of a callbox, a 102-mm diameter by 4267-mm steel pole conforming to ASTM A 500, with an A.B.Chance auger foundation, a "Call Box" sign, a "TTY" sign, a unity gain antenna, and a 6.5 Watt solar panel. The poles were equipped with rectangular slip base mounting hardware consisting of (4) 5/8- 11 UNC 3 1/4" long hot-dipped galvanized SAE J429 GD 2 hex bolts and J995 GD 2 nuts. SAE wide Type A plain washers were used against the faces of the nuts and bolts and between the slip base plates. All mating surfaces of the slip base plates, washer surfaces, and bolt threads were rubbed down with a layer of paraffin wax. The supports were augured 1664 mm (65.5 inches) into "weak" soil, and the slip base nuts were torqued to 54 N-m prior to testing. The hardware and torque specifications differ from those shown in the enclosed illustration of the tested support.

A summary of the crash tests is presented in the following table.

Test #



NCHRP 350 Designation



Vehicle Mass

834.4 kg

809.4 kg

Vehicle Impact Speed

38.09 km/h

101.05 km/h

Soil Type

Weak (S-2)

Weak (S-2)

Impact Angle

20 degrees

20 degrees

Test Article Mass 1

103 kg

103 kg

Occupant Impact Speed

1.49 m/s

2.30 m/s

Vehicle Velocity Change

4.25 km/hr (1.18 m/s)

7.02 km/hr (1.95 m/s)

Windshield Damage

None, no contact

None, no contact

Vehicle Deformation 2

Major roof dents, 89 mm max

Major bumper, body dents

Stub Height

Approximately 75 mm

Approximately 75 mm


  1. The test article mass includes the pole, slip base assembly, and callbox, signs, and solar panel assemblies. That part of the test article which remains in the soil is included in this total even though it does not have to be put in motion by the test vehicle.

  2. The 89 mm maximum deformation of the roof is within the 125-mm tolerance allowed by FHWA for roof deformation under impact by luminaire supports in a memorandum dated August 19, 1994.

The tested supports met the change in velocity and stub height requirements of the AASHTO Standard Specifications and NCHRP Report 350. There were no excessive deformations of the passenger compartment and no damage to the windshield. Therefore, the callbox supports are acceptable for use on the National Highway System (NHS) within the range of conditions tested, when requested by a State. The "weak" soil testing was the "worst-case scenario" for any slip-base design. Therefore the Comarco Wireless Technologies' TTY Call Box support system will be acceptable when installed in strong soil as well. Should you wish to use the same slip base mechanism on a support embedded in concrete, that too will be acceptable if the foundation is adequate to support the typical structural loadings imposed by such an installation. To prevent misunderstanding by others, this letter of acceptance, numbered SS-84, shall not be reproduced except in full.

Our acceptance is limited to the breakaway characteristics of the supports and does not cover the structural features, compliance with the Americans with Disabilities Act, nor the devices' conformity with the Manual on Uniform Traffic Control Devices. Presumably, users will be provided with sufficient information on structural design and installation requirements to ensure proper performance of the supports. Comarco Wireless Technologies should provide certification to other transportation agencies wishing to use this breakaway support system that the hardware furnished will have essentially the same chemistry, mechanical properties, and geometry as those used in the tests and that they will meet FMWA change in velocity requirements.

Sincerely yours,

[Original signed by Dwight A. Horne]
Dwight A. Home
Director, Office of Highway Safety Infrastructure

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