FEB 2 4 |997

ACTION: Nebraska and South Dakota Road
Closure Gates

Chief, Federal-Aid and Design Division HNG-14

Mr. Arthur E. Hamilton
Regional Administrator (HEO-07)
Kansas City, Missouri

This is in reply to your December 13, 1996, memorandum requesting
the Federal Highway Administration's (FHWA) acceptance of the
Nebraska road closure gate as meeting crashworthiness
requirements for use on the National Highway System (NHS).
Transmitted with your memorandum was a report dated January 1995,
of tests conducted on a South Dakota road closure gate at the
Midwest Roadside Safety Facility (MWRSF) and an analysis by

Dr. Dean L. Sicking of the Nebraska version of the gate.

Both gates are built of square tubular aluminum, and are mounted
on breakaway posts. The South Dakota design is 8.5 meters long
and the Nebraska design is 11 meters long. Drawings of both
gates are attached, along with a drawing and description of the
breakaway hardware common to the support and end posts for both
gates. Your request was for FHWA acceptance of the Nebraska
modification. However, since this office had not previously
reviewed the crash testing of the South Dakota design, we will
take this opportunity to examine and act on both gate designs.

Full-scale crash testing was-conducted to assess the breakaway
performance of the 8.5-meter-long South Dakota road closure gate.
It was tested in the “open” position, as this was considered the
most likely “worst case” condition. It was also tested with the
gate downstream of the principal support post.

Requirements for breakaway supports are found in the American
Association of State Highway and Transportation Officials'
(AASHTO) Standard Specifications for Structura Supports for

i Signs minaire: id affic Signals. These
specifications have been adopted by the FHWA. Guidelines
established in the National Cooperative Highway Research Program
(NCHRP) Report 350 were used to conduct the tests and analyze
their results.

Form DOT F 1320.65
Supersedes previous edition OFFICIAL FILE COPY


A summary of the crash tests of the South Dakota design, and

estimated values

for the Nebraska Design are presented below:

Test Number Target Values SDG-1 SDG-2 NEB LO* NEB HI*
Test Article Mass, kg na 68 68 91 91

Gate Length, m wa 8.5 8.5 i i
Vehicle Mass, kg 820 794 794 7194 194
Impact Speed, km/h 35.0 or 100.0 37.1 95:5. 35 100.
Breakaway Device n/a Transpo** Transpo** ‘Transpo** ‘Transpo**
Bolt Circle Diameter, mm wa 36 36 ee ot
Occupant Impact Speed, m/s 5.0 maximum. aul 4.2 est 3.3: est 4.6
Vehicle Velocity Change, m/s 5.0 3.6 Bull oo i“

Stub Height, mm. 100 maximum 76 <100 ecu eles

*These two columns contain the values estimated by Dr. Sicking
of the MWRSF. This design was not crash tested.

**Model No. 201 Pole-Safe ®(1-inch, frangible, die cast
aluminum couplings produced by Transpo Industries, Inc.)

***Bolt circle diameter was not specified. However,

at as)

recommended that the same bolt layout pattern be used as was

crash tested.

****Transpo Couplings can be expected to leave stubs no greater

than 100 mn.

The results of the tests SDG-1 and SDG-2 meet the change-in-

velocity and stub-height requirements adopted by the FHWA.
South Dakota road closure gate is, therefore, acceptable for use
on the NHS, within the range of conditions tested, if proposed by
a State. All posts supporting the gate in the open and closed
positions are to be of breakaway designs.
test conditions was the impact direction.
acceptable for use where it can struck head-on, on the opposite
impact end. We concur that the estimated
values for the Nebraska design are within our requirements and it
is also acceptable for use, with the same orientation limitation
as that for the South Dakota design.

end from the test

The

Note that one of the
Thus, it is not

Our acceptance is limited to the breakaway characteristics of the
slip-base mechanism and the crashworthiness of the gate

installations, and does not cover their structural features.



Presumably the States will develop sufficient information on
structural design and installation requirements to ensure proper
performance.

Dwight A. Home

Dwight A. Horne

Attachments

Federal Highway Administration

HNG-14: NArtimovich: 366-1331: gmorton: 2-19-97:R7
copies to:

HNG-1 HNG-10 HNG-14 Reader, 3128 File, 3128
RAs HFL-1 HSR-20 HHS-10

Geometric and Safety Design Acceptance Letter Number LS-46