Refer to: HSA-10/SS-121
Ms. Linda Lee
MTC SAFE Project Manager
Joseph P. Bort Metro Center
101 Eighth Street
Oakland, California 94607-4700
Dear Ms. Lee:
Thank you for your letter of November 13, 2003, requesting Federal Highway Administration (FHWA) acceptance of the MTC SAFE ITS Callbox support as a breakaway sign support system for use on the National Highway System (NHS). Accompanying your letter was a report from the Texas Transportation Institute and videos of the crash tests. You requested that we find the MTC SAFE ITS Callbox breakaway supports 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."
Testing of the supports was in compliance with the guidelines contained in 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.
The MTC SAFE ITS Callbox support includes the callbox main housing constructed of Lexan polycarbonate. The support poles were manufactured by A.B. Chance. Each pole was 102 mm (4 inch) outside diameter by 6096 mm (240 inches) long, schedule 40, galvanized steel pipe with a four-bolt unidirectional slip base welded to the base of the pole. The pole was attached atop a 1524 mm (60 inch) long galvanized steel auger foundation in NCHRP Report 350 strong soil. The height from the ground surface to the top of the auger foundation slip plate was 76 mm (3 inches). Four 16 mm x 76 mm (5/8 inch x 3 inch) long Grade 2 bolts with nuts, lock washers and three SAE wide Type A flat washer (one washer between the slip planes) per bolt, torqued to 58 Nm (48.2 ft-lb), were used to attach the support to the foundation stub.
Two 762 mm x 914 mm (30 inch x 36 inch) call box sign panels and two 254 mm x 508 mm (10 inches x 20 inches) TTY sign panels were attached back to back to the support pole. At the top of the support was a pole cap with a 20 watt solar panel (34 mm x 430 mm x 530 mm) and antenna. A simulated CCTV camera, weighing 3.8 kg (8.4 pounds) was mounted to the support 5793 mm from the ground. A drawing of the tested system is enclosed for reference.
The weights of the components and of the total system are listed for reference below:
|ITS Call Box Item Description||Mass in kg||Weight in pounds|
|6 m (20 ft) steel pole||83.1||183|
|ITS Call Box (battery removed)||20.4||45|
|Call Box Signs (2)||4.9||11|
Full-scale automobile testing was conducted on the commission'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||Occup. Speed||Delta V|
|474240/08-6 3-60||34.5 km/h||1.0 m/s (3.3 ft/sec)||4.2 km/hr|
|474240/08-7 3-61||99.2 km/hr||1.9 m/sec (6.2 ft.sec)||7.6 km/hr|
Occup. Speed: Occupant Impact Speed: Speed at which a theoretical front seat occupant will contact the windshield. Delta V: Change in speed of the test vehicle.
Damage was limited to the front bumper, hood, radiator, roof, and rear hatch, with no windshield contact occurring in either test. Velocity changes were all within acceptable limits, and the only stub remaining was the 76-mm tall lower slip plate. The results of testing met 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. Because the occupant impact speed was well below the "desirable" limit of 3 m/s, the additional weight of the battery will not have a significant effect on the breakaway performance of the system.
Please note the following standard provisions that apply to FHWA letters of acceptance:
(Original Signed By R. Powers)
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety