ID: nht74-1.6

DATE: 09/11/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: International Harvester

TITLE: FMVSS INTERPRETATION

TEXT:

SEP 11 1974

Mr. K. W. Berner Manager Component Design & Development International Harvester Truck Division Engineering 2911 Meyer Road Fort Wayne, Indiana 46803

Dear Mr. Berner:

This is in reply to your letter of August 13, 1974, to Dr. Gregory asking for confirmation of your interpretation of S5.3.1(b) of Motor Vehicle Safety Standard No. 105.

Paragraph S5.3.1(b) states that an indicator lamp shall be ?????? whenever there is "A drop in the level of brake fluid in a master cylinder reservoir to less than . . . one-fourth of the fluid reservoir capacity in any reservoir compartment ...." This will confirm that the lamp must activate whenever the fluid in any compartment is less than one-fourth the capacity of that compartment, rather than one-fourth the total capacity of the reservoir regardless of the number of compartments.

Yours truly,

Richard B. Dyson Acting Chief Counsel

ID: nht74-1.7

DATE: 12/18/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

Dec 18 1974 N40-30 (TWH)

Mr. J. R. Farron Group Director of Engineering The Bendix Corporation 401 Bendix Drive P. 0. Box 4001 South Bend, Indiana 46634

Dear Mr. Farron:

This responds to your undated letter which requests a determination that the Bendix "Hydro-boost" qualifies as a brake power assist unit" as that term is defined in Standard No. 105-75. You describe the unit as designed with a "push through" cabability in both the "normal" and "failed power" operating conditions, and with an accumulator that permits low pedal effort for a limited number of brake applications after a power failure has occurred.

The following definitions distinguish a "Brake power assist unit" from a "Brake power unit":

"Brake power assist unit" means a device installed in a hydraulic brake system that reduces the operator effort required to actuate the system, and that if inoperative does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control.

"Brake power unit" means a device installed in a brake system that provides the energy required to actuate the brakes, either directly or indirectly through an auxiliary device, with the operator action consisting only of modulating the energy application level.

In the preaamble to Notice 8 of Docket No. 70-27, we made the further clarification that the capabilities of the unit in the "failed power" condition determine whether it is a brake power assist unit. A copy of this discussion is enclosed. Because the Bendix "Hydro--boost" in the "failed power" condition does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control (i.e.. with "push through" capability), it qualifies as a brake power assist unit under the definitions of Standard No. 105-75.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

Enclosure SECURITY=000

ID: nht74-1.8

DATE: 10/16/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Volkswagen of America, Inc.

TITLE: FMVSS INTERPRETATION

TEXT:

OCT 16 1974 NOA-30 (ZTV)

Mr. Joseph W. Kennebeck, Manager Emissions, Safety & Development Volkswagen of America, Inc. Englewood Cliffs, N. J. 07632

Dear Mr. Kennebeck:

This is in reply to your letter of September 24, 1974. You informed us that Volkswagen intends to introduce a new model, the Rabbit, in January 1975 that meets all requirements of Standard No.105-75 except S5.3.1.(b), requiring a brake fluid reservoir capacity indicator, which it will meet as of September 1, 1975. You also informed us that "one version of the Rabbit which meets FMVSS 105-75 exceeds the currently required preburnish check permissible pedal force." You therefore asked for an "interpretation of whether the Volkswagen Rabbit could comply with FMVSS 105-75 except for S5.3.1.(b) prior to September 1975, in lieu of complying with FMVSS 105 in effect up to that time."

In our view, the fact that the Rabbit exceeds the maximum specified preburnish check pedal force does not by itself indicate a failure to comply with existing Standard No. 105. Paragraph S4.1 of Standard No. 105 requires the performance ability of a passenger car service brake system to be "not less than that described in Section D of Society of Automotive Engineers Recommended Practice J937, 'Service Brake System Performance Requirements - Passenger Cars', June 1966." and tested in accordance with SAE Recommended Practice J843c, 'Brake System Road Test Code - Passenger Cars', June 1966." Section D of J937, Preburnish check, subreferences "SAE J843, Section C item 1".

The subreferenced item says that the purpose of the preburnish check is "to allow for a general check of instrumentation, brakes, and vehicle function," rather than a test of the effectiveness of the service brake system. Thus the preburnish check is not actually a test requirement. Although the distinction between test requirements, conditions and procedures is not made in the SAE materials incorporated into Standard No. 105, the successor Standard No. 105-75 distinguishes the three. It makes brake burnish part of the test procedure and sequence. Burnishing appears in the test procedure section, S7.4, and Table I, showing test requirements and corresponding procedures, does not relate it to any of the requirements of S5.

A manufacturer's certification covers only the performance requirements of the standard, and is his representation that if testing is conducted in the manner the standard specifies, the vehicle will meet those requirements. Therefore, no "waiver" of Standard No. 105-75 or amendment to Standard No. 105 appears necessary for Volkswagen to certify that the Rabbit complies with Standard No. 105, assuming, of course, that it meets all actual performance requirements of that standard.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

ID: nht74-1.9

DATE: 03/15/74

FROM: AUTHOR UNAVAILABLE; J. B. Gregory; NHTSA

TO: General Motors Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in further reply to your letter of November 19, 1974, petitioning the NHTSA to amend Part 567, Certification (@ 567.4(f)), to allow the use of certification labels on which the lettering is embossed or engraved without regard to whether it contrasts with its background.

The NHTSA has decided that your petition should be denied. Our experience has been that certain types of engraving, those that are stencil-typed or stamped, are difficult to read without color contrast. The NHTSA considers it essential that certification labels be readable under all lighting conditions, and has not found embossing or engraving to produce by themselves sufficiently readable lettering for these labels. Of course, there is no prohibition against embossing or engraving if the finished lettering contrasts with its background.

We appreciate your point that Standard No. 105a accepts embossed or engraved lettering on the master cylinder reservoir label without requiring a color contrast. We are presently considering amending Standard No. 105a to eliminate this discrepancy.

ID: nht74-2.1

DATE: 01/17/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Aeroquip Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your request of January 8, 1974, made to Mr. Herlihy of this office, for an interpretation of S5.1.2.3 of Standard No. 121, Air brake systems, as it applies to a check valve which is designed to bleed back no more than 5 psi pressure from the service reservoir toward the source of air pressure.

The check valve described in the specification you enclosed would satisfy the requirements of S5.1.2.3 as long as there is no air loss in excess of the designed bleed off, and that total air loss never lowers the pressure at any time below the air compressor "cut in" pressure.

Yours truly,

ATTACH.

AEROQUIP CORPORATION/INDUSTRIAL DIVISION

January 4, 1974

John Womack and Richard Dyson -- Chief Council, National Highway Traffic Safety Administration

Gentlemen:

This letter is a request for approval of our XFF9260-50 check valve for use in truck and bus air brake systems as detailed in the Motor Vehicle Safety Standards #121, Paragraph S5.1.2.3.

The function of the subject check valve is to allow air bleed back of no more than 5 psi pressure from the maximum pressure setting on the primary reservoir. The purpose of the air bleed back is to increase the service life of our Aerofiner Air Purifier (P/N FF9260-01). The air volume used off the #1 air reservoir (pre-dried air) is used to back flush the desiccant bed in the Aerofiner at approximately 3 cfm until the pressure in the reservoir drops to the relief valve setting, (5 psi below maximum reservoir operating pressure) at which time the valve is completely closed. In all other respects, it functions as a typical safety check valve.

Attached is a layout sketch of the subject check valve showing the seal surfaces and flow paths under various conditions.

Also attached, is a copy of Bulletin #5212, describing our Aerofiner brake system air purifier.

Please supply me in writing, the council's approval of our XFF9260-50 check valve in truck and bus air brake systems.

If there are any questions, feel free to contact me.

Sincerely yours

Donald T. Fischer -- Project Engineer, Coupling Section

ID: nht74-2.10

DATE: 11/07/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Columbia Body & Equipment Co.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to CBE's October 24, 1974, question whether a trailer equipped with a telescoping drawbar that varies the distance between axles to conform to various State regulations would qualify as a "Heavy hauler trailer" as that term is defined in Standard No. 121, Air brake systems:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) Its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @ 393.106 of this title.

The answer to your question is no. The extension of the drawbar is not an "extension of the vehicle frame." This characteristic is intended only to describe trailers whose function necessitates a highly specialized configuration that significantly interferes with brake design. In contrast, the telescoping drawbar is not related to the trailer's function, but simply permits the vehicle to conform to State highway regulations.

Yours truly,

ATTACH.

October 24, 1974

Acting Chief Consel -- U.S. Dept. of Transportation

Attn: Richard Dyson

Dear Mr. Dyson;

Does the Pony Trailor on our drawing number T65-497 (enclosed) qualify as a heavy hauler trailer and exempt from the S121 or any other antiskid requirement until Sept. 1, 1976 as Mr. Tadd Herllhy defined in our phone conversation Oct. 23, 1974. Please reply as soon as possible.

Sincerely yours,

COLUMBIA BODY & EQUIPMENT COMPANY

John C. Hansen -- Sales Manager

ID: nht74-2.11

DATE: 08/19/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Dura Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Dura Corporation's July 24, 1974, questions whether S5.6 of Standard No. 121, Air brake systems, requires parking brakes on air suspension liftable axles, and whether the "no lockup" requirements of the standard apply to a liftable axle on a "tandem axle rig".

The parking brake performance options of S5.6 do not require parking brakes on an air suspension liftable axle such as you describe. S5.6.2 requires only that the parking brakes installed on a vehicle meet minimum performance levels. S5.6.1 requires parking brake retardation force on "an axle other than a steerable front axle". We do not consider this requirement to apply to an axle which is not on the ground when the parking brake system is activated.

The standard's "no lockup" requirement (S5.3.1) applies to

"any wheel at speeds above 10 mph except for . . .

(b) Lockup of wheels on nonsteerable axles other than the two rearmost nonliftable, nonsteerable axles on a vehicle with more than two nonsteerable axles.

Under this provision, if a vehicle has two nonliftable, nonsteerable axles at the rear which do not lock up (such as an antilock-equipped tandem axle rig) it may be equipped with a liftable nonsteerable axle which does not meet the "no lockup" requirements.

Yours truly,

July 24, 1974

Sidney F. Williams -- Office of Operating Systems, National Highway Traffic Safety Administration, Department of Transportation

Dear Sir:

Dura Corporation is presently involved in manufacturing add-on liftable axle/suspension assemblies which are marketed with OEM and body builders. Due to the impending effectivity dates of FMVSS 121 we are presently preparing to equip our products to comply. Our liftable airide axle/suspension assemblies are applicable to both pusher and tag situations.

The intent of this letter is to request an official interpretation of FMVSS 121. Our present understanding of the standard is as follows:

An anti-lock system will be required with the add-on axle/suspension if added to a single axle rig but not required if added to a tandem axle rig.

II. An emergency/parking spring brake will not be required with the add-on axle/suspension. This supposition is based on a loss of air pressure will automatically lift the axle rendering the spring brake inoperable.

Please indicate if the above statements are correct. Your consideration and cooperation in this matter is truly appreciated.

Sincerely,

Raymond E. Jones, Project Engineer -- DURA CORPORATION

cc: W. Locke

ID: nht74-2.12

DATE: 11/14/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Truck Trailer Manufacturers Association

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your October 23, 1974, question in behalf of Steadman Containers, Ltd., asking if Standard No. 121, Air brake systems, applies to the Steadman "liftainer", which is described as a semi-trailer frame capable of carrying 20- and 40-foot cargo containers that are loaded by means of cranes mounted at each end of the semi-trailer. The vehicle is used to move containers in terminal areas and is used on the highway only in relocation to another terminal.

The "liftainer" is a motor vehicle as that term is defined in the National Traffic and Motor Vehicle Safety Act of 1966, because it uses the highway on a necessary and recurring basis to move between work sites. A discussion of the motor vehicle definition is enclosed for your information. As a motor vehicle, it is subject to the requirements of Standard No. 121 for trailers, effective January 1, 1975.

I have also enclosed a discussion of Standard No. 121's applicability to vehicles purchased by Canadians for use between Canadian and United States points. The standard would apply to Steadman trailers if they are purchased for use on U.S. highways.

Yours truly,

ATTACH.

October 23, 1974

James B. Gregory -- National Highway Traffic Safety Administration, Department of Transportation

Dear Dr. Gregory:

Could you please furnish us with an interpretation in connection with the enclosed described equipment and its relationship with the anti-skid devices to be placed on equipment by January 1, 1975?

You will note that Steadman containers indicates that "The Liftainer Container handling unit is not intended, nor used, as a highway unit, but is used in terminals where it is moved by means of a conventional highway tractor. Its highway use is limited only to possible occasional re-positioning from one yard to another. As its width in the closed, unfolded condition, is in excess of 8', road movement always involves use of special permits."

We will appreciate your consideration and response to the above.

Sincerely yours, Charles J. Calvin -- President

ID: nht74-2.13

DATE: 09/30/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Nabors Trailers, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your August 21, 1974, question whether a "logging pole trailer", which consists of a beam to which an axle-mounted bolster can be clamped at different points to accomodate different log lengths, qualifies as a heavy hauler trailer as that term is defined in Standard No. 121, Air brake systems:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) Its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @ 393.106 of this title.

This also acknowledges receipt of your September 5 and September 17, 1974, letters on the same subject.

The logging pole trailer you describe is a heavy hauler trailer, and as such, Standard No. 121 does not apply to this trailer until September 1, 1976. The beam or "reach", together with the bolster, constitutes the frame of the trailer, and the brake lines are designed to adapt to extension of the bolster element along the beam.

This arrangement differs from the standard highway van which has a one-piece frame with an adjustable tandem axle. The purpose of this sliding arrangement is unrelated to an extension of the frame itself to accomodate the transportation of heavy or oversize loads.

Yours truly,

ATTACH.

NABORS TRAILERS, INC.

Sept. 17, 1974

Sidney Williams -- National Highway Traffic Safety Administration

Dear Mr. Williams:

It should be of interest and concern to the National Highway Traffic Safety Administration that we have not had the sight nor the specifications nor the price of a brake equipped axle assembly that can be certified to meet the requirements of Federal Motor Vehicle Safety Standard 121. We are wholly dependent upon the one source for our brake axle assemblies. From that source we have been told that they have encountered one delay after another in their program to develop and test brakes that will meet the new requirements. Their best hope now is that by the end of October they will be able to give us technical information and sometime in November they will be able to begin shipping certifiable brakes.

The same situation prevails with respect to wheel and drum assemblies. Our supplier of drums have told us that they are conducting tests now and that they should be able to tell us in November what drums will be required for compliance with the new Safety Standard.

You can guess from this information the predicament in which we find ourselves when trailers that we put into production in December scheduled for completion in January will be required by law to be in compliance with SS 121. We are certain that there are many other trailer manufacturers who are dependent upon the same sources of supply that we are who are in the same predicament. There may be other sources of supply for brake axle assemblies and for wheels and drums who are ready to describe and certify their products to meet the new Safety Standard, but we, for one, could not at this time get in schedule with new suppliers.

Sincerely yours, B. H. Smith -- President

NABORS TRAILERS, INC.

Sept. 5, 1974

Sidney Williams -- National Highway Traffic Safety Administration

Dear Mr. Williams:

On November 15, 1973 I sent a collection of our pole trailer catalogs and of photographs of logging pole trailers in service to the Truck Trailers Manufacturers Association in Washington. I thought that these had been sent over to your offices. Perhaps they never did get there. My letter went to Mr. M. L. Higgins who at that time was handling these matters for TTMA, and very shortly after that he resigned and Mr. Burt Weller took his place.

With this letter I am sending you two each of our Catalog 196 and our Form 198 describing our standard types of pole trailers.

The logging pole trailers described in Catalog 196 are those about which we are primarily concerned with respect to MVSS 121. Those trailers are designed and used exclusively in logging operations and move logs from the woods to the saw mills or to storage areas. Logging pole trailers are subjected to unbelievably difficult conditions, or at least unbelievable to those who have never witnessed difficult logging operations. Maintaining brakes and lights on logging pole trailers when the very minimum of equipment is used is difficult and often impossible. When the hardware that is required for compliance with MVSS 121 is added to braking equipment as now being used, the difficulties of maintenance will be multiplied and the likelihood that the brakes will be kept operational is reduced.

On the inside of Catalog 196 you will see good views of the rear assembly of our two popular models, the Logmaster and the SPR. These two trailers are identical in capacity and in usage, and the two models are built simply because some loggers like one type and some like the other. In both models you will see that the rear bolster sits on a frame that sits on the two-spring suspension that sits on the axles. A pole or drawbar connects the front bolster assembly to the rear assembly. The rear assembly can slide along the pole to change the distance between the front and rear bolsters to accommodate various log lengths. If you look closely you will see that the rear assembly is locked into place on the pole by means of clamping collors around the coupling pole ahead of and behind the rear assembly. Also, for safety purposes a pin is dropped through the pole at the rear to avoid the possibility that the trailer might slide off the pole.

You will see in the illustrations that the two hoses for the brakes and the cable for the lighting on the rear assembly are connected to the truck or to the front bolster assembly at the front and are connected to the rear assembly at the rear with quick detachable couplings. You will see that when the distance between the bolsters is relatively short these brake and light lines must be coiled up and supported by the pole. If the trailer should be extended in length, the full length of these lines would be required. It is a characteristic of these trailers that the brake lines are designed to adapt to permitting the distance between the front and rear bolsters to contract and to expand.

Another common practice in the use of logging pole trailers is to load the rear frame assembly on the back end of the truck when the trailer and truck are being carried unloaded back into the woods. This practice is for both economic and safety reasons. When the rear assembly is loaded on the truck the brake lines must be disconnected. Also, no part of the brake system can extend below the bottom of the axles because the axles must rest on the truck frame or on the runners that are put on the truck frame to carry the trailer.

When you look closely at these pictures of these logging pole trailers you will observe that the space between the axles and the load-carrying bolster is limited and is filled with equipment with current types of brakes. The trailers shown have only one air reservoir. In order to comply with MVSS 121 another larger air reservoir will have to be added. There simply is no place to put it on these logging pole trailers without interfering severely with their intended usage. If in addition to this other air reservoir we must add spring-loaded power chambers and the valves and logic boxes and electrical connections required for the anti-skid brake system, it is up to now inconceivable to us how to add that hardware in such a way that it could reasonably be expected to stay on the trailers when they are used in the log woods.

The Models TP and TPC Pole Trailers illustrated in our Form 198 are designed and used primarily for hauling pipe and poles and reinforcing rods and long steel beams and other, long and self-supporting objects. The same difficulties in adding the anti-skid brake equipment and the spring loaded power chambers apply to these trailers as to the logging pole trailers. However, since these two models are used primarily on improved roads the difficulties of maintaining the equipment would not be as great. Trailers of these two models constitute no more than perhaps 50 units a year for us. They do have the same characteristic of logging pole trailers in that the brake lines are designed to be adapted to permitting the distance between the front and rear bolsters to change. There would be the same difficulties on these trailers in getting the speed of brake application and release that there would be on other pole trailers.

I can understand the difficulty of writing an exemption for any one class or category of trailers without letting the exemption be subject to unintended interpretations. However, it has seemed to me since we first became concerned with the problems of MVSS 121 that pole trailers as defined in Part 371.3 of the Federal Motor Vehicle Safety Standards could be exempted without any reasonable misunderstandings. Pole trailers as defined in Part 371.3 were exempted from the requirements of MVSS 108 and have been exempted from certification requirements. I have not understood why they could no also be exempted from MVSS 121, and I think that their categorical exemption would be beneficial rather than detrimental to the highway safety program. I have made all of these statements previously in letters to the National Highway Traffic Safety Administration and to the Truck Trailer Manufacturers Association.

We appreciate very much your consideration of our problems and I thank you again for your telephone call on September 3rd in response to our letter of August 21st.

If it might be helpful to giving you and others concerned a better understanding of our problems, which we think are shared by many others, I would be willing to come to Washington for a conference.

Sincerely yours, B. H. Smith -- President

Enclosures

NABORS TRAILERS, INC.

August 21, 1974

Sidney Williams -- National Highway Traffic Safety Administration

Subject: FMVSS 121 - Air Brake Systems, Docket #74-10, Notice 5

Dear Mr. Williams:

We are unable to determine from the subject Notice 5 and from the discussions and considerations that preceded it whether or not it is the intention of NHTSA that Logging Pole Trailers be considered "Heavy Hauler Trailers" within the definition of that category.

In one way of looking at it nearly all Logging Pole Trailers come within Characteristic (1) of the definition because the brake lines are designed to adapt to permitting the rear frame assembly of the pole trailer to slide on the pole or drawbar and thereby to adapt to extension or contraction of the effective length between the load bearing members. In another way of looking at it, pole trailers would not come within Characteristic (1) because there is no actual separation or extension of the vehicle frame. Actually, in pole trailers there is no frame as such connecting the front and rear load bearing members.

The one consistent and definitive characteristic of pole trailers, as we understand them, is that they consist of a front bolster that rests on the towing tractor and a rear bolster that rests on the trailer suspension and axles with the two connected with a pole on which the rear assembly can slide forward and backward.

In some logging operations the length between the front and rear bolsters is changed frequently, maybe daily. In some operations the length between the bolsters is changed only as the species or types of logs being hauled change. In some operations, on every unloaded trip the rear assembly is moved forward on the pole and is loaded on the truck to be hauled back into the woods. Since logging conditions and practices require different effective lengths between the front and rear bolsters and different problems with respect to the brake lines, practically all of our Logging Pole Trailers are rigged out with quick disconnectors for the brake and light lines at the rear assembly, and to that extent the rigging is similar to that on extendable platform trailers. The difficulties of maintaining good air line connections and unrestricted flow of air are certainly as great on pole trailers as on extendable frame trailers.

There are other inherent problems in applying and maintaining brakes on Logging Pole Trailers that in our opinion should be considered before there is a requirement upon trailer manufacturers to add anti-skid devices, spring loaded power chambers, dual or triple air reservoirs, and the other hardware that goes with the system. For example, up to now we have not been able to devise a way to put spring loaded power chambers on the axles of Logging Pole Trailers without swinging them under the axles. We definitely do not have sufficient clearance for putting the spring loaded power chambers over the axles with the suspensions and construction that we are using now. To put the (Illegible Word) chambers under the axles on pole trailers that are destined for the logging woods is, in our opinion, impracticable. The operators will not be able to keep the power chambers in place. The net result will be that they will knock them off or take them off the trailers and run the trailers without brakes. We run into similar but not insoluble problems with respect to installing additional air reservoirs and all of the other wiring and hardware required in an anti-skid system, but the trailers will have to be redesigned, they will be made substantially more expensive, and they will be less suited to their purpose.

Opinions have been expressed that we should simply assume that the definition of Heavy Hauler Trailers does embrace Logging Pole Trailers and that we should bother ourselves and our customers no more about the problem. We are not willing to leave it there because we cannot afford to be found in violation of the law and to be required to go back and add equipment which we did not furnish when the trailers were built. If we must put the anti-skid equipment on Logging Pole Trailers we must be getting ready for it in our designs and in our production methods, and we must be preparing our customers for the added cost and for the maintenance problems that will be inevitable.

Pole Trailers make up hardly more than 1% of the truck trailers that are manufactured. According to the Bureau of the Census Industrial Report for May, 1974, 189 pole trailers were shipped in May 1974, 214 in April 1974, and 177 in May 1973. For ourselves, the total volume in pole trailers is less than 300 units per year, but that is a substantial portion of our total volume and we are one of the largest suppliers of such trailers to the Southern lumber industry. Could you tell me exactly where we stand with respect to Logging Pole Trailers and MVSS 121?

Sincerely yours, B. H. Smith -- President

ID: nht74-2.14

DATE: 09/30/74

FROM: R. B. Dyson; NHTSA

TO: Royal Industries

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your August 28, 1974, question whether a "logging pole trailer", which consists of a beam to which an exle-mounted bolster can be clamped at different points to accommodate different log lengths, qualifies as a heavy hauler trailer as that term is defined in Standard No. 121, Air brake systems:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @@393.106 of this title.

The logging pole trailer you describe is a heavy hauler trailer, and as such, Standard No. 121 does not apply to this trailer until September 1, 1976. The beam or "reach", together with the bolster, constitutes the frame of the trailer, and the brake lines are designed to adapt to extension of the bolster element along the beam.