1200 New Jersey Ave., SE

 Washington, D.C. 20590

March 30, 2011

In Reply Refer To:

HSST/LS-72

Mr. Zach Thiemann, E.I.T.

Associate Product Development Engineer

Valmont Industries, Inc. 

7002 North 288th Street

P.O. Box 358

Valley, NE 68064-0358

Dear Mr. Thiemann:

This letter is in response to your request for the Federal Highway Administration (FHWA) 

acceptance of roadside safety systems for use on the National Highway System (NHS).

Name of system: Valmont Decorative Clamshell Base Covers 

Type of system: Breakaway Luminaire Support Structure

Test Level: NCHRP Report 350 Test Level 3

Testing conducted by: Valmont-MwRSF/UNL Pendulum Facility

Date of request: September 24, 2010

Date of completed package: September 24, 2010

Request initially acknowledged: September 30, 2010

You requested that we find these systems acceptable for use on the NHS under the provisions of 

the National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended 

Procedures for the Safety Performance Evaluation of Highway Features.” 

Requirements

Roadside safety devices should meet the guidelines contained in the National Cooperative 

Highway Research Program (NCHRP) Report 350 or the American Association of State 

Highway and Transportation Officials’ (AASHTO) Manual for Assessing Safety Hardware 

(MASH). Requirements for breakaway supports are those in the AASHTO Standard 

Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Signals. 

Decision

The following devices were found acceptable:

• Valmont decorative bases over TRANSPO Couplings on certain poles as detailed in this 

letter.
2

Description

Clamshell base covers are installed on luminaire poles for aesthetic purposes. The Valmont 

Industries system described in this submission includes (1) a breakaway system; (2) a decorative 

clamshell base; (3) a pole; and (4) a luminaire arm. 

For the breakaway system, four 1 inch (25 mm) diameter TRANSPO Industries double neck, 

pole safe, couplings were used to fasten the pole to the foundation as shown in Enclosure 1. 

These couplers were previously accepted in FHWA acceptance letter LS-45B dated on 

January 16, 1997.

Valmont Industries evaluated five different styles of decorative clamshell bases in this request 

namely, (1) Huntington; (2) Washington; (3) Harrisburg; (4) Memphis; and (5) Osceola. Each 

may be fabricated in multiple sizes to accommodate various luminaire poles. The decorative 

clamshell bases are cast in two halves from either a 319F or 356F aluminum alloy. The two 

halves are bolted together using four 3/8 inch (10 mm) diameter bolts, two near the top and two 

near the bottom. The clamshell does not attach directly to the pole but only wraps around the 

base of the pole and rests on the ground. Design details for each of the models are shown in 

Enclosure 4 through 24. 

Valmont Industries fabricates various poles and luminaire arms. In order to test the system, one 

of the Valmont Industries taller, thicker, and heavier poles was selected. The round steel pole 

was fabricated with a 7-gauge (4.55 mm) wall thickness and had a height of 38 feet, 6 inches 

(11.7 m). The nominal height to the luminaire was 45 feet (13.7 m). The pole had a top outside 

diameter of 4-1/2 inches (114 mm) and a bottom outside diameter of 10-3/8 inches (263 mm). 

A handhole was located on the pole centered at a height of 1 foot, 6 inches (0.5 m) from the base 

of the pole. Two mounting points for luminaire arms were located 6 inches (152 mm) and 33 

inches (838 mm) from the top of the pole. The pole is shown in Enclosure 2. The pole base 

plate, 1 inch (25 mm) thick by 14 inches (356 mm) square, was welded to the bottom of the pole. 

The bolt circle was 13-1/2 inches (343 mm) in diameter. 

The luminaire arm attached to the pole had a length of 15 feet (4.6 m) as shown in Enclosure 3. 

The arm was braced with two struts at locations of 5 feet and 10 feet (1.5 m and 3m) laterally 

from the pole. 

Crash Testing

Pendulum testing was conducted on the test articles described above by 

Valmont-MwRSF/UNL Pendulum Facility. The testing was conducted according to NCHRP 

350 test designation 3-60. The following table shows test IDs, clamshell styles tested, and 

weights of pieces of each test article. 

Test ID Clamshell 

Style

Clamshell 

Size 

(inch)*

Clamshell 

Weight (lb)

Pole Weight 

(lb)

Luminaire 

Arm Weight 

(lb)

LST-353-04 Huntington 24 47 548 175

LST-353-05 Washington 30 113 548 175

LST-381-01 Memphis 18 57 571 165

LST-381-02 Harrisburg 22 56 571 165

LST-381-03 Osceola 24 89 571 165
3

* Base Diameter

Summaries of test results for tests LST-353-04 and LST-353-05 are shown in Enclosures 25 and 

26 respectively. Enclosures 27 through 29 summarize test results for tests LST-381-01 through 

LST-381-03 respectively. 

 

Findings

According to the NCHRP 350, test designation 3-60 and test designation 3-61 are to be 

conducted for support structures for Test Level 3 approval. In both tests full scale automobile 

testing with an 820C small car is required. As described before, five pendulum tests were 

conducted as a surrogate for a low speed test with an 820C vehicle. In these tests occupant 

impact velocity, occupant ridedown acceleration, and maximum vehicle speed change (where 

measured) were found to be within the acceptable limits of NCHRP 350. The couplings and 

luminaire poles broke away in a consistent and predictable manner. The base of the pole rotated 

away from impact to allow a vehicle to travel underneath it. Therefore, the test article passed the 

low speed test.

The breakaway system used includes TRANSPO Industries double neck bolts. In tests 

LST-381-01 through LST-381-03, two bolts broke at the upper neck. In test LST-353-04, one 

bolt broke at the upper neck and in test LST-353-05 all bolts broke at the lower necks. For those 

bolts that broke at the upper neck, remaining stubs were 6 inches above the ground whereas 

those broke at the lower neck had stubs remaining that were 3 inches above the ground. The 

AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaries, and 

Traffic Signals require that any “substantial remains” of the breakaway support not project 

greater than 4 inches above ground level to avoid vehicle undercarriage snagging. It was judged 

that the stubs in these crash tests that measured more than 4 inches would not present a 

significant hazard. This was due to the fact that the breakaway elements of the stubs, the lower 

neck, was present and thus the remaining stubs are themselves breakaway systems which would 

give way on subsequent impact, reducing potential snagging. 

FHWA allows the results of the high speed tests to be estimated using data from the low-speed 

test in combination with an analytical extrapolation method described in the FHWA 

memorandum “Identifying Acceptable Highway Safety Features” dated on July 25, 1997. For all 

five test articles, the high speed test extrapolation analysis resulted in change in velocity values 

for the high speed tests above the NCHRP 350 limit of 5.0 m/s and all five test articles failed the 

test. 

The equation for extrapolation to obtain results for the high speed test includes mechanical 

properties of the test article, the speed at which low speed and high speed tests are conducted, 

and the speed change of the test vehicle during the low speed test. It is intuitive that in both low 

speed and high speed tests, a heavier pole with greater moment of inertia/radius of gyration and

longer luminaire would cause more speed change for the impacting vehicle. As described in this 

letter, Valmont Industries selected critical poles and luminaire arm combinations (i.e., tall, 

heavy, thick poles with long luminaire arms) for the low speed tests. Experience has shown that 

any less critical (lighter) poles will cause smaller speed change for the impacting vehicles. 

In your request, you have estimated the results of the high speed tests for various combinations 

of poles, luminaire arms, and clamshell bases that Valmont Industry fabricates using the 

analytical equation. In these estimations you used the speed changes obtained from the low 

speed tests which are more conservative speed changes for these less critical combinations. 
4

Therefore, if the result of the extrapolation for each combination satisfies the requirements of 

NCHRP Report 350, I agree that the combination passes test 3-61. 

The following tables illustrate all combinations which passed test 3-60 and 3-61. These poles 

can be used with single or twin arms shorter or equal to 15 ft or top mount luminaries weigh less 

than 150 pounds where applicable. In these tables, the cells containing “X” represent the pole 

and aesthetic clamshell base covers that are compatible with each other and determined to pass 

both tests. It should be noted that a pole that falls between any two poles shown in these two 

tables is also acceptable and can be used on the NHS provided that all other conditions of this 

letter are satisfied. 

It should be noted that the pole, luminaire arm, and clamshell base covers must meet the 

conditions and limitations of TRANSPO Industries breakaway couplings identified in FHWA 

acceptance letter LS-45B particularly the followings:

• All supports shall be mounted to a structural concrete foundation that will not move in 

the soil if the support is struck be a vehicle.

• Luminaire mounting height should not exceed 15.7 meters (55 feet). 

• Mass of pole, mast arm, luminaire and other hardware above the couplings shall not 

exceed 454 kg (1000 lbs.). 

Therefore, the system described in the requests above and detailed in the enclosed drawings is 

acceptable for use on the NHS under the range of conditions tested, when such use is acceptable

to a highway agency. 

Pole Aesthetic Clamshell Base Covers

Family 

- Type

Shaft 

Length 

(ft)

Mounting 

Height 

(ft)

Thickness 

(ga.)

Base 

O.D. 

(in.)

Huntington Washington Memphis Harrisburg Osceola

24 17 12 30 24 18 18 15 22 24 17

DS30 20 21 11 5.90 X X X X

DS30 25 26 11 5.90 X X X X

DS30 30 31 11 6.60 X X X X X

DS30 35 36 11 7.30 X X X X X X

DS30 35 36 11 8.50 X X X X X

DS30 39 40 11 9.00 X X X X

DS50 17 20 11 5.90 X X X X

DS50 17 20 11 6.50 X X X X X

DS50 22 25 11 5.90 X X X X

DS50 22 25 11 7.00 X X X X X

DS50 27 30 11 6.60 X X X X X

DS50 27 30 11 7.50 X X X X X X

DS50 30 32 11 6.60 X X X X X

DS50 30 32 11 8.00 X X X X X X

DS50 32 35 11 7.30 X X X X X X

DS50 32 35 11 8.00 X X X X X X

DS50 37 40 11 9.00 X X X X

DS50 42 45 11 9.50 X X X

DS60 20 25 11 6.50 X X X X X

DS60 20 25 11 7.00 X X X X X

DS60 25 30 11 7.00 X X X X X

DS60 25 30 11 7.50 X X X X X X

DS60 25 30 11 8.00 X X X X X X

DS60 30 35 11 8.00 X X X X X X

DS60 30 35 11 8.50 X X X X X

DS60 35 40 11 9.00 X X X X
5

DS70 22 25 11 7.00 X X X X X

DS70 27 30 11 7.50 X X X X X X

DS70 27 30 11 8.00 X X X X X X

DS70 32 35 11 8.00 X X X X X

DS70 32 35 11 8.50 X X X X X

DS70 32 35 11 9.00 X X X X

DS70 37 40 11 9.00 X X X X

DS70 37 40 11 9.50 X X X

DS32 28.5 30 11 7.50 X X X X X X

DS32 28.5 30 11 8.00 X X X X X X

DS32 33.5 35 11 8.00 X X X X X X

DS32 33.5 35 11 8.50 X X X X X

DS32 33.5 35 11 9.00 X X X X

DS32 38.5 40 11 9.00 X X X X

DS32 38.5 40 11 9.50 X X X

DS32 38.5 40 11 10.00 X X X

DS32 43.5 45 11 9.50 X X X

DS32 43.5 45 11 10.00 X X X

X = Passes Requirements for all Luminaire Arm Possibilities

= Aesthetic Clamshell Base Not Compatible With Pole 

Pole Aesthetic Clamshell Base Covers

Family 

- Type

Shaft 

Length 

(ft)

Mounting 

Height 

(ft)

Thickness 

(ga.)

Base 

O.D. 

(in.)

Huntington Washington Memphis Harrisburg Osceola

24 17 12 30 24 18 18 15 22 24 17

DS210 20 20 11 5.90 X X X X

DS210 20 20 11 6.50 X X X X X

DS210 25 25 11 5.90 X X X X

DS210 25 25 11 7.00 X X X X X

DS210 25 25 7 7.00 X X X X X

DS210 30 30 11 6.60 X X X X X

DS210 30 30 11 8.00 X X X X X X

DS210 35 35 11 7.30 X X X X X X

DS210 35 35 11 8.50 X X X X X

DS210 35 35 11 9.50 X X X

DS210 39 39 11 7.82 X X X X X X

DS210 39 39 11 9.00 X X X X

DS210 45 45 11 10.00 X X X

DS210 50 50 11 10.00 X X X

FL210 20 20 11 6.72 X X X X X

FL210 25 25 11 7.30 X X X X X X

FL210 25 25 7 7.75 X X X X X X

FL210 30 30 11 8.00 X X X X X X

FL210 30 30 7 8.00 X X X X X

FL210 35 35 11 8.45 X X X X X

FL210 35 35 7 9.00 X X X

FL210 39 39 11 9.00 X X X X

FL210 39 39 7 10.00

Custom 20 23 7 6.00 X X X X

Custom 20 23 7 7.00 X X X X X

Custom 25 28 7 6.00 X X X X

Custom 25 28 7 7.00 X X X X X

Custom 25 28 7 7.75 X X X X X X

Custom 25 28 7 8.00 X X X X X

Custom 30 33 7 7.00 X X X X X

Custom 30 33 7 7.75 X X X X X X

Custom 30 33 7 8.00 X X X X X

X = Passes Requirements for all DS70 Luminaire Arm or Top Mount Possibilities

= Aesthetic Clamshell Base Not Compatible With Pole 
6

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

• This acceptance is limited to the crashworthiness characteristics of the systems and does not 

cover their structural features, nor conformity with the Manual on Uniform Traffic Control 

Devices.

• Any changes that may adversely influence the crashworthiness of the system 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 system being marketed is 

significantly different from the version that was crash tested, we reserve the right to modify or 

revoke our 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 it will meet the crashworthiness requirements of the FHWA and the NCHRP 

Report 350. 

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

LS-72 and shall not be reproduced except in full. This letter and the test documentation upon 

which it is based are public information. All such letters and documentation may be reviewed 

at our office upon request. 

• The Decorative Clamshell Bases are patented products and considered proprietary. If 

proprietary systems are specified by a highway agency for use on Federal-aid projects, except 

exempt, non-NHS projects, (a) they must be supplied through competitive bidding with 

equally suitable unpatented items; (b) the highway agency must certify that they are essential 

for synchronization with the 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.

• This acceptance letter shall not be construed as authorization or consent by the FHWA to use, 

manufacture, or sell any patented system for which the applicant is not the patent holder. The 

acceptance letter is limited to the crashworthiness characteristics of the candidate system, and 

the FHWA is neither prepared nor required to become involved in issues concerning patent 

law. Patent issues, if any, are to be resolved by the applicant.

Sincerely yours,

Michael S. Griffith

Director, Office of Safety Technologies

Office of Safety

29 Enclosures