ID: nht76-4.20

DATE: 02/12/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: General Teamsters Local 959 - Alaska

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 29, 1976, questions whether an owner-operator of a vehicle manufactured to comply with Standard No. 121, Air Brake Systems, may legally disconnect portions of the brake system after a vehicle is delivered, or specify that the vehicle be delivered without certain portions of the brake system installed. Your members are asking about the antilock portion of the brake systems installed to meet the "no lockup" provisions of the standard (S5.3.1).

Two provisions of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. @ 1381 et seq.) are involved. Section 108(a)(1)(A) prohibits the sale of any vehicle unless it complies with all applicable safety standards that were in effect on the date of the vehicle's manufacture. This means that a member cannot purchase a newly-constructed tractor with portions of the brake system disconnected, if those portions are installed in compliance with the standard. The antilock portions of the system are, as far as I know, installed in compliance with the standard and therefore cannot be disconnected prior to sale.

Section 108(a)(2)(A) with which you are familiar prohibits, with one exception, knowing disconnection of the antilock system by manufacturers, distributors, dealers, or repair businesses. Thus, there is no prohibition on disconnection by an owner-operator of his own vehicle's system under the Traffic Safety Act. However, other State of Federal statutes, or the regulations of the Bureau of Motor Carrier Safety may prohibit disconnection. In any case, the NHTSA urges that you not disconnect safety devices without consultation with the vehicle manufacturer with regard to the safest configuration of the vehicle.

SINCERELY

General Teamsters Local 959 State of Alaska

January 29, 1976

Frank A. Berndt, Acting Chief Counsel U. S. Department of Transportation National Highway Traffic Safety Administration

Several of our members have obtained copies of your letter of September 29, 1975 to Mr. Joseph L. Casson, concerning Standard Number 121 and Section 108 (a) (2)(A) of the National Traffic and Motor Vehicle Safety Act. In that letter, you stated that manufacturers of air braked buses that conform to Standard Number 121 may instruct the owners of his products to disconnect the anti-lock system used to meet the Standard. For the period necessary to correct a safety-related defect in the system that may make its operation hazardous.

Several members of Local 959 either operate tractors or are in the process of obtaining newly built tractors. They have requested that I contact you to obtain your opinion on if they may disconnect the anti-lock system in the existing tractors, or not have an anti-lock system placed on their tractors which are presently being constructed. They are of the opinion that no anti-lock system currently on the market is safe. In other words, they wish to disconnect or not have placed on the newly constructed tractors any anti-lock system until the safety-related defects in the anti-lock system are corrected. If the anti-lock systems were disconnected, the defect report requirement of 49 CFR Part 573 and the defect notification requirements of 49 CFR Part 577 would be complied with.

Thanking you in advance for your attention to my request,

James A. Witt, General Counsel

CC: BILL SHANNON -- COPPER FREIGHT LINES

ID: nht76-4.21

DATE: 05/13/76

FROM: AUTHOR UNAVAILABLE; S. P. WOOD for F. Berndt; NHTSA

TO: Rome Engineering & Manufacturing Co.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Remco's April 26, 1976, question whether an exclusion from a safety standard based on the gross axle weight rating (GAWR) of an axle is met by using the rating of the axle beam by its manufacturer, or whether the truck or trailer manufacturer must also consider the load-bearing abilities of the wheels, rims, and hubs used with the axle beam.

Gross axle weight rating is defined in 49 CFR 571.3 to mean:

. . . the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tireground interfaces.

This definition means that the determination of GAWR is made by the vehicle manufacturer and that the axle beam rating of the component supplier cannot be the only basis for GAWR calculation. The GAWR is the value established at the tire-ground interfaces at each wheel position, and this means that the wheels, rims, hubs, and tires must be included in the determination. Thus, with regard to the exclusion from Standard No. 121, Air Brake Systems, until September 1, 1977, for any vehicle with an axle that has a GAWR of 24,000 pounds or more, the vehicle manufacturer must take into consideration each component on the axle as well as its attachment to the vehicle frame.

Sincerely,

ATTACH.

ROME ENGINEERING & MANUFACTURING CO.

April 26, 1976

TAD HERLIHY -- OFFICE OF CHIEF COUNSEL -- National Highway Safety Administration

Dear Sir:

We are in need of clarification of Motor Vehicle Safety Standard No. 121 as pertains to paragraph S3 of Part 571-S121-1, quote: "or that has a gross axle weight rating for any axle of 24,000 pounds or more."

Does this mean that a certification from the axle manufacturer that his product is rated at 24,000 pounds or more would exempt the trailer manufacturer from compliance with MVSS 121 or is it necessary to have a single axle as well as the tires, wheels, hubs, and rims on that axle rated at 24,000 pounds or more capacity before the exemption is valid?

We would appreciate an advisory opinion on this matter.

Thank you.

Very truly yours,

R. A. Plummer -- Vice President & General Manager

ID: nht76-4.22

DATE: 08/02/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: MOTAC Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Motac's June 24, 1976, request to know why a trailer with a flat cargo-carrying surface that is not more than 40 inches above the ground is considered a "heavy hauler trailer" (as defined in Standard No. 121, Air Brake Systems), while a trailer with an inclined cargo-carrying surface that is more than 40 inches above the ground over the fifth wheel attachment point is not considered a heavy hauler trailer. You also request confirmation that the period for exclusion of heavy hauler trailers from the standard has been extended to September 1, 1977.

At the time that the "heavy hauler trailer" exclusion was implemented, the agency considered and rejected the addition of trailers with inclined beds to the excluded category. I have enclosed a copy of the notice that implemented the exclusion, which states "The NHTSA has concluded that trailers with beds higher than 40 inches (including trailers whose beds are below 40 inches over the wheels but higher than 40 inches over the fifth wheel) can accommodate the new larger brake packages available at this time." Of course the exclusion was intended to and does apply to the traditional trailer with a gooseneck and a flat cargo-carrying surface that is not more than 40 inches above the ground. The "double-drop semi", the "stock drop frame flat-bed", and the "40'-0" single axle drop frame platform semi" you describe appear to qualify as heavy hauler trailers.

I have enclosed a copy of the amendment of Standard No. 121 that extends the date for exclusion of heavy hauler trailers to September 1, 1977.

Yours truly,

Enclosures

ATTACH.

June 24, 1976

Frank Berndt -- Acting Chief Counsel, DEPT. OF TRANSPORTATION

Subject: Clarification regarding installation of FMVSS-121 brakes on "Low Bed Heavy Hauler Trailers."

Dear Sir,

We would appreciate further clarification if FMVSS-121 brakes are required or are exempt on the Drop Frame Platform Semi-Trailer per our attached drawing SK-7229-W3. This Drop Frame Platform Semi-Trailer is also made with Tandem axles and a platform height of 39".

In accordance with my letter of Aug. 7, 1975 addressed to Mr. James B. Gregory and his reply "N40-30 of Sept. 8, 1975 (copies attached) I interpret that this type of trailer is exempt from the S-121 brakes as it complies to the definition of a Low Platform Heavy Hauler Trailer."

We also received from T.T.M.A., a copy of your letter, file No. N40-30 RFBPI (copies attached) with two sketches of similar type trailers, stating that they do not qualify for exemption of the S-121 brake system.

Since the greater majority of the load is carried on the main deck, which I interpret as the "Primary Cargo Carrying Surface" and only a small portion of the load can be carried on the gooseneck platform, I analyze that this complies with your definition of Low Platform Heavy Hauler Trailers.

Also please advise if your Docket No. 75-16, Notice 5 has become effective to extend the installation of the S-121 brake system on Heavy Hauler Trailers until Sept. 1, 1977 as I do not have a confirming copy in my files.

Yours very truly,

Jack A. Johnson -- Chief Engineer, MOTAC, INC.

Enc.

ID: nht76-4.23

DATE: 08/16/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Truck Equipment & Body Distributors Association

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your July 28, 1976, request for confirmation that a boat-carrying trailer which has a primary cargo-carrying surface less than 40 inches from the ground qualifies as a "Heavy hauler trailer", and that such trailers are not required to meet the requirements of Standard No. 121, Air Brake Systems, until September 1, 1977.

"Heavy hauler trailer" is defined in the standard as follows:

"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 boat-carrying trailer which you describe as having a bed height of 18 3/4 inches would qualify for exemption until September 1, 1977.

Yours truly,

ATTACH.

TRUCK EQUIPMENT & BODY

DISTRIBUTORS ASSOCIATION

July 28, 1976

Chief Counsel -- National Highway Traffic Safety Administration, Department of Transportation

Gentlemen:

We are writing on behalf of a member company who has received a large order for some boat trailers, per the enclosed photograph.

The trailer is 42 feet in overall length, and eight feet wide. The "primary carrying surface" is 18 3/4 inches high, although the gooseneck portion at the front of the trailer is 48 inches high and 79 inches long. The vehicle will be equipped with 12 1/4 inch by 5 inch air brakes.

We agree with our member that this unit is exempt from FMVSS 121, since it meets the definition of a "heavy-hauler trailer". However the member would appreciate your agreement just to be on the safe side.

Thank you for your assistance in this matter.

Sincerely,

THOMAS S. PIERATT/LW -- Executive Director

Enclosure:

[Graphics omitted]

ID: nht76-4.24

DATE: 04/07/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Trail-O-Matic, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your March 8, 1976, request to know the status of "log trailers" under Standard No. 121, Air Brake Systems, whether the exclusion for "heavy hauler" trailers terminates September 1, 1976, and what the penalties are for non-compliance with an applicable Federal motor vehicle safety standard. You indicate that you may know of some manufacturers that do not comply with Standard No. 121 and suggest that all persons concerned with the standard be advised of the status of the regulation.

Without description of the "log trailers" in question, it is not possible to determine if Standard No. 121 applies to them. Most pole trailers and trailers equipped with any axle having a gross axle weight rating of 24,000 pounds or more are examples of vehicles that may be excluded from the standard. Mr. Herlihy of this office has already sent applicable documents to you under separate cover.

The exclusion from the standard for "heavy hauler" trailers was extended recently and now terminates September 1, 1977.

Section 108(a)(1) of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. @ 1397(a)(1)) prohibits the sale and false or misleading certification of a non-complying vehicle to which a standard is applicable. Each violation of these provisions makes the manufacturer liable to a maximum civil penalty of $ 1,000 for each violation, up to a total of $ 800,000 for a related series of violations. (15 U.S.C. @ 1398). You may advise our Office of Standards Enforcement of any violations of which you are aware.

The NHTSA finds it impracticable to notify directly every interested person of each of its regulatory actions. Each action is made public and is widely distributed by commercial services and trade associations. Enclosed is an information sheet that explains the various means to obtain copies of our regulations.

YOURS TRULY,

Trail-O-Matic, Inc.

March 8, 1976

Richard B. Dyson, Assistant Chief Counsel U. S. DEPARTMENT OF TRANSPORTATION National Highway Traffic Safety Administration

RE: N40-30 (TH)

With reference to "anti-skid" brake regulation # 121 we have strictly conformed to all terms and conditions of the above but wish to report some our competition in Georgia and Florida are building log trailers without installing the anti-skid equipment.

It isn't quite fair to comply with the rules and then miss some sales because competition is selling much cheaper because the unit is not equipped to the D. O. T. # 121 requirement.

What are the penalties, if any, for not complying with this requirement OR has anything been changed basically that we are not aware of?

As a suggestion I think the government should advise all concerned as to the status of this regulation in order to clear the air and put everyone on equal footing.

Please let me hear from you as soon as possible with reference to the above and also will the September 1, 1976 date be applicable on low bed machinery trailers.

Thanking you for your prompt attention, we are

J. L. Chancey President

ID: nht76-4.25

DATE: 06/30/76

FROM: AUTHOR UNAVAILABLE; John Womack for F. Berndt; NHTSA

TO: Wayne Daniel Truck, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your June 18, 1976, request for permission to substitute pre-121 brake components for certain components of the brake systems on trucks and trailers you own that were manufactured in conformity with Standard No. 121, Air Brake Systems.

From your description, I assume that you intend to remove portions of the brake system that were installed in satisfaction of the requirements of S5.3.1 of Standard No. 121. Section 108(a)(2)(A) of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. @ 1397(a)(2)(A)) prohibits, with one exception, knowing disconnection of the antilock system by a manufacturer, distributor, dealer, or repair business.

A person that does not fall into there categories is not prohibited from disconnection of the systems. Thus, it would be permissible for you to make such modifications on your own trucks and trailers. Other State or Federal requirements, such as those of the Bureau of Motor Carrier Safety for operation in interstate commerce, may prohibit disconnection. In any case, the NHTSA urges that you not disconnect safety devices without consulting the vehicle manufacturer with regard to the safest configuration of the vehicle.

SINCERELY,

Wayne Daniel Truck, Inc.

June 18, 1976

Thomas Herliky Office of Chief Counsel National Highway Traffic Safety Admin.

Our firm is planning to purchase some new trucks in the near future. Since we have had difficulty with the 121 brake we would like to replace the brake with the pre-121 brake.

Please let me know as soon as possible if we will be in violation if we do this.

W. Wayne Daniel

ID: nht76-4.26

DATE: 09/09/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: B. F. Goodrich Engineered Systems Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your July 26, 1976, question whether the "no lockup" requirement of S5.3.1 and S5.3.2 of Standard No. 121, Air Brake Systems, requires wheel sensors on both axles of a tandem axle system in those cases where the "no lockup" performance is provided by means of an antilock system. I have enclosed a detailed discussion of this issue that responded to a similar question from another manufacturer. The response should answer your question.

Yours truly,

Enclosure

ATTACH.

B.F. Goodrich Engineered Systems Company

July 26, 1976

JOHN W. SNOW -- ADMINISTRATOR -- National Highway Traffic Safety Administration

Subject: REQUEST FOR CLARIFICATION OF MVSS 121

Gentlemen:

Section S.5.3.1.A (for trucks and buses) and Section S.5.3.2.A (for trailers) of MVSS 121 states that wheel lock-up shall not occur on any wheel above 10 M.P.H., except for controlled lock-up of wheels allowed by an anti-lock system.

It is understood that a manufacturer is not required to utilize an anti-lock system to meet the "no lock-up" requirement, however, if a manufacturer does choose to utilize the "controlled lock-up" exception of S.5.3.1.A and S.5.3.2.A, by installing an anti-lock system, it must control the lock-up of the wheels which are pneumatically controlled by that system (reference attached copy of letter dated March 7, 1975 to Harold D. Shall from James C. Shultz). Therefore, it is our interpretation that the vehicles' anti-lock system, if included, must include a wheel speed sensor on each wheel, that is pneumatically controlled by the anti-lock logic module valve. Is this correct?

We will appreciate your official ruling on this pressing matter at your earliest convenience.

Very truly yours,

Richard J. Brandewie -- Program Manager, Highway Products

cc: D. L. Haines; C. D. McCarty

ID: nht76-4.27

DATE: 09/03/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Freightliner Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your July 23, 1976, question whether the "no lockup" requirement of S5.3.1 of Standard No. 121, Air Brake Systems, requires wheel sensors on both axles of a tandem axle system in those cases where the "no lockup" performance is provided by means of an antilock system. Sections S5.3.1 (trucks and buses) and S5.3.2 (trailers) specify that the vehicle shall, under various load, road surface, and speed conditions, be capable of stopping

. . .without lockup of any wheel at speeds above 10 mph, except for:

(a) Controlled lockup of wheels allowed by an antilock system. . .

(b) * * * * *

This basic requirement is stated in performance terms, permitting a manufacturer to choose any brake system design that will ensure that the wheels do not lock up under the specified conditions.

The exception to the "no lockup" requirement set forth above permits "controlled lockup of wheels allowed by an antilock system." Manufacturers demonstrated, during the course of rulemaking, that properly functioning antilock systems might be designed to allow wheel lockup for a fraction of a second, and that antilock design should not be inhibited by a prohibition on all lockup. The agency made the "controlled lockup" exception a part of the standard (36 FR 3817, February 27, 1971) and has subsequently interpreted the term to permit manufacturers latitude in the design of their systems.

In compliance with the basic requirement, most manufacturers have equipped each axle of a vehicle with a valve to regulate the air pressure that applies the brakes, sensors at each wheel to send a signal when a wheel is locking up, and a logic module that receives the signals and instructs the valve when to release air pressure to prevent lockup ("axle-by-axle control"). Recently, some manufacturers have simplified their systems by utilizing only one valve and logic module to modulate the air supply to both axles of the typical tandem axle system found on many trucks and trailers ("tandem control"). Two approaches to wheel sensor placement have been used for tandem control systems. If it is possible to predict which of the two axles will lock first during braking, sensors may be placed on this axle only, knowing that reduced air pressure in response to a signal from the "sensed" axle will also release the brakes on the "unsensed" axle. In other cases, where it is not possible to predict which axle will lock first, tandem control systems may have sensors on all four wheels of the tandem.

In November 12, 1974, and March 7, 1975, letters of interpretation to Dana Corporation, the NHTSA confirmed that a manufacturer may choose the number of wheel speed sensors and logic modules that he includes in his antilock system. Thus, tandem control is not prohibited by the standard, regardless of the number of wheel speed sensors provided. When Dana asked if lockup on the unsensed axle of a single-axle sensor system would qualify for the "controlled lockup" exception of the requirement, the agency said that it would not, reasoning that the logic module would not exert effective control over the lockup of the unsensed axle without benefit of input signals from wheels on that axle. Therefore, according to the Dana interpretation, the unsensed axle in a single-axle sensor system could not be allowed to lock at all, even momentarily, during the service brake stopping test. No data of actual performance was submitted with the Dana letter.

Your letter argues that the NHTSA's interpretation of "controlled lockup" (to Dana Corporation) creates an anomalous and unjustified restriction on the use of "tandem control." Your submission, and data received by the agency from other interested persons, demonstrate that the Dana interpretation does not adequately reflect the degree of control which a single-axle sensor system actually can exert over the unsensed axle of a tandem system. Based on analysis of the submitted data, it appears that the amount of lockup permitted on unsensed axles is closely controlled by the permitted on unsensed axles is closely controlled by the available antilock systems. While there is a measurable difference in stopping performance between "axle-by-axle" control and "tandem control," the standard already permits either of these means to satisfy the requirements. When the narrower question of the performance difference between sensors on one or both axles is analyzed, it is apparent that virtually no difference exists in the stopping distance of vehicles equipped these two ways. The effective lateral stability available during a stop also appears comparable regardless of placement of sensors on one or both axles. A technical report summarizing these findings will be placed in the public docket as soon as possible.

For this reason, and based on review of test unavailable at the time of the Dana interpretation, the agency concludes that its interpretation of "controlled lockup" in response to the question posed by Dana should be, and is hereby, withdrawn. It is the agency's interpretation that the "controlled lockup" exception is not dependent on the number or location of sensors used in an antilock installation.

Sincerely,

ATTACH.

FREIGHTLINER CORPORATION

July 23, 1976

LEGAL COUNSEL -- National Highway Traffic Safety Administration

Re: Motor Vehicle Safety Standard No. 121 (49CFR571.121)

Dear Sir:

Freightliner Corporation, a manufacturer of light-weight heavy-duty air braked vehicles, is vitally affected by the requirements of FMVSS-121. Therefore, we are requesting a clarification of the exemption contained in S5.3.1, for "controlled lockup of wheels allowed by an antilock system." In reading the requirements of Standard No. 121, the exemption to the "no wheel lockup" requirement contained in S5.3.1 clearly applies to any wheel of a tractor, truck or bus which is subject to the control of an antilock system. But in a previous interpretation on this subject (March 7, 1975, letter of James C. Shultz to Harold D. Shall, Dana Corporation), the Acting Chief Cousel appeared to limit this exemption only to wheels which are equipped with antilock wheel speed sensors. Clearly, this interpretation is design restrictive in that it is stated in design rather than performance terms. Further, this interpretation does not take into consideration the possibility of alternate means for achieving controlled wheel lockup, such as mechanical drives which interlock both tandem axles.

The results of recent tests conducted by Freightliner show that the wheels on both tandem axles of a tandem axle vehicle can be effectively controlled through the use of one antilock system sensing wheel speeds from only one axle, and demonstrate that "controlled lockup" typical of that provided by axle-by-axle antilock systems can be achieved through a combination of suspension design, controlled brake actuation timing, and antileck system design. The test results (see attachment) indicate that the vehicle equipped with only one antilock controller meets the stopping distance requirements of FMVSS-121 with performance equivalent to that of vehicles equipped with the more complex and costly axle-by-axle antilock systems currently employed.

Since tractors and trucks, such as those manufactured by Freightliner Corporation, are subject to stopping distance requirements under a variety of road and load conditions, efficient utilization of available traction for braking is already a requirement of the standard for powered vehicles. Therefore, we believe that requiring the use of axle-by-axle antilock systems is unnecessary to ensure efficient utilization of available traction for braking of powered vehicles. Accordingly, we request interpretation of the requirements of S5.3.1 which is:

1. Stated in performance rather than design criteria.

2. Which does not impose a more strigent requirement for axles which are not equipped with wheel speed sensors (but subject to the control or an antilock system) than the "controlled lockup" requirement applicable to wheels which are equipped with wheel speed sensors.

If further information is necessary or desirable, we would be pleased make a technical presentation to you and appropriate members of the NHTSA staff, which would include a discussion of our test results along with movies of the tests.

Respectfully submitted,

Ray W. Murphy -- Director, Research and Development

Attach. FMVSS-121 STOPPING DISTANCE TEST DATA

Vehicle - Three Axle COE Tractor, 138" Wheelbase Control Axle Loads (lbs.) Steering Drive Trailer Loaded 10,480 34,110 33,290 Bob tail 7,550 6,040 -

Brakes Size Actuation Power Linings Steering Axle 15x4 14 degrees x9 ABB-551D Drive Axle 15x7 12 degrees x12 (Dual) ABB-551D

Average service brake stopping distances in ft., vehicle equipped with tandem control antilock system (numbers in parenthesis are values from tests of similarly configured vehicle equipped with axle-by-axle antilock control system)* Loaded Bobtail FMVSS-121 Requirement 20 MPH Dry Asphalt 33.6 27.6 35 (SN 75) Test Surface (34.0) (26.4) 60 MPH Dry Asphalt 259.8 251.2 293 (SN 75) Test Surface (253.7) (225.5) 20 MPH Wet Slippery 58.8 60.2 ** (SN 20) Test Surface (71.3) (57.3)

* Freightliner CTC Report No. T081-75/12, November 20, 1975

** 60 ft. on SN 30 test surface

ID: nht76-4.28

DATE: 09/03/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Frehauf Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your August 17, 1976, question whether the "no lockup" requirement of S5.3.1 of Standard No. 121, Air Brake Systems, requires wheel sensors on both axles of a tandem axle system in those cases where the "no lockup" performance is provided by means of an antilock system. Sections S5.3.1 (trucks and buses) and S5.3.2 (trailers) specify that the vehicle shall, under various load, road surface, and speed conditions, be capable of stopping

. . . without lockup of any wheel at speeds above 10 mph, except for:

(a) Controlled lockup of wheels allowed by an antilock system. . .

(b) * * * * *

This basic requirement is stated in performance terms, permitting a manufacturer to choose any brake system design that will ensure that the wheels do not lock up under the specified conditions.

The exception to the "no lockup" requirement set forth above permits "controlled lockup of wheels allowed by an antilock system." Manufacturers demonstrated, during the course of rulemaking, that properly functioning antilock systems might be designed to allow wheel lockup for a fraction of a second, and that antilock design should not be inhibited by a prohibition on all lockup. The agency made the "controlled lockup" exception a part of the standard (36 FR 3817, February 27, 1971) and has subsequently interpreted the term to permit manufacturers latitude in the design of their systems.

2

In compliance with the basic requirement, most manufacturers have equipped each axle of a vehicle with a valve to regulate the air pressure that applies the brakes, sensors at each wheel to send a signal when a wheel is locking up, and a logic module that receives the signals and instructs the valve when to release air pressure to prevent lockup ("axle-by-axle control"). Recently, some manufacturers have simplified their systems by utilizing only one valve and logic module to modulate the air supply to both axles of the typical tandem axle system found on many trucks and trailers ("tandem control"). Two approaches to wheel sensor placement have been used for tandem control systems. If it is possible to predict which of the two axles will lock first during braking, sensors may be placed on this axle only, knowing that reduced air pressure in response to a signal from the "sensed" axle will also release the brakes on the "unsensed" axle. In other cases, where it is not possible to predict which axle will lock first, tandem control systems may have sensors on all four wheels of the tandem.

In November 12, 1974, and March 7, 1975, letters of interpretation to Dana Corporation, the NHTSA confirmed that a manufacturer may choose the number of wheel speed sensors and logic modules that he includes in his antilock system. Thus, tandem control is not prohibited by the standard, regardless of the number of wheel speed sensors provided. When Dana asked if lockup on the unsensed axle of a single-axle sensor system would qualify for the "controlled lockup" exception of the requirement, the agency said that it would not, reasoning that the logic module would not exert effective control over the lockup of the unsensed axle without benefit of input signals from wheels on that axle. Therefore, according to the Dana interpretation, the unsensed axle in a single-axle sensor system could not be allowed to lock at all, even momentarily, during the service brake stopping test. No data of actual performance was submitted with the Dana letter.

Your letter argues that the NHTSA's interpretation of "controlled lockup" (to Dana Corporation) creates an anomalous and unjustified restriction on the use of "tandem control." Your submission, and data received by the agency from other interested persons, demonstrate that the Dana interpretation does not adequately reflect the degree of control which a single-axle sensor system actually can exert over the unsensed axle of a tandem system. Based on analysis of the submitted data, it appears that the amount of lockup permitted on unsensed axles is closely controlled by the available antilock systems. While there is a measurable difference in stopping performance between "axle-by-axle"

3

control and "tandem control," the standard already permits either of these means to satisfy the requirements. When the narrower question of the performance difference between sensors on one or both axles is analyzed, it is apparent that virtually no difference exists in the stopping distance of vehicles equipped these two ways. The effective lateral stability available during a stop also appears comparable regardless of placement of sensors on one or both axles. A technical report summarizing these findings will be placed in the public docket as soon as possible.

For this reason, and based on review of test data unavailable at the time of the Dana interpretation, the agency concludes that its interpretation of "controlled lockup" in response to the question posed by Dana should be, and is hereby, withdrawn. It is the agency's interpretation that the "controlled lockup" exception is not dependent on the number or location of sensors used in an antilock installation.

Sincerely,

ATTACH.

FRUEHAUF DIVISION / FRUEHAUF CORPORATION

August 17, 1976

Chief Counsel NHTSA Gentlemen:

RE: 49 CFR 571.121

In our evaluation of anti-lock systems, Fruehauf has become convinced that a considerable economic improvement can be made in the system provided for FMVSS 121. A system involving sensors on one axle, a logic controlling that axle, and a second axle of the suspension controlled by the same logic, performs identically to a system on the same suspension that uses sensors on each wheel and a logic for each axle. The economic gains for trailer users is very attractive. This system conforms with the 121 standard in its entirety and no change in the standard is requested.

We have exhibited in many tests, that our suspension provides mechanical control of lock-up. The momentary lock-up of the second axle of the suspension is always initiated at a slightly later time than the front axle. When we use an air and electrical system as described above, we can assure that the release of air to the two axles is simultaneous. Therefore, the second axle performance in lock-up is equal to or slightly better than the first axle. See charts in Appendix B of typical tests.

Both axles are under the control of an anti-lock system. The control is such that any momentary lock-up on the axle without sensors is equal to or shorter than momentary lock-up with sensors. This is possible through the geometry of the suspension. The suspension has equal loads on the axles at rest. However, with the application of brakes, one axle reduces load, transferring load to the second axle momentarily. This transfer assures that the first axle always locks or reduces speed faster than the second axle. The effect of this system of anti-lock is that the average of the two wheels of the front axle controls both axles. No wheel is allowed more than momentary lock-up.

2

The suspension described above is different from that on which Dana Corporation requested an interpretation some time ago. However, the letters of interpretation in answer to Dana are general enough that they should be clarified so they do not restrict our use of this system. Those interpretations say that an axle must have sensors if it is to be allowed to have momentary lock-up. This requirement does not seem justified in this instance since it requires the axle without sensors to perform better than the axle with the complete sensor and logic system. Certainly, we agree that the axle-by-axle complete control system adequately controls the braking function and stability of a trailer. Wheel-by-wheel systems were not significantly better. We believe that a "slave" axle that performs as well as those controlled axles in all respects, should be adequate even though mechanical control is used rather than sensors in each wheel.

While stopping distances is not a test requirement on trailers, it is an important safety factor. Considerable testing with measured stopping distances has been done with both bogie control and axle-by-axle control. Best stopping distances are secured with systems which allow momentary zero wheel speed intervals on low mu surfaces. A system tuned to give no lock-up or zero wheel speed would give longer stopping distances. While there are differences in some instances with one system having shorter distance than the other, the variations are not as great between bogie control and axle control of a given anti-lock system on a given trailer, as they are between two manufacturers' anti-lock systems. See Appendix A. Therefore, the use of bogie control does not change the stopping distance beyond the ranges already exhibited by variations in anti-lock systems.

In all of the testing that has been done with bogie control, we've had no indication of lack of stability.

Air consumption, which is not a test requirement but is a factor in the selection of systems, is not significantly different.

Systems on which we have seen test data using four sensors with a single logic, do not perform better than the bogie control described here.

In the interest of providing the most economical system that meets the requirements and intents of FMVSS 121, Fruehauf is considering production of the described system of anti-lock where any momentary lock-up on any wheel is of equal or shorter time than any momentary lock-up on the wheel using electrical speed sensors.

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We request your prompt confirmation that the described system complies with FMVSS 121. If NHTSA has any questions about this systems' compliance, Fruehauf would request an early response to avoid any economic loss or inconvenience to the trailer customers.

Sincerely,

A. F. Hulverson Vice President Engineering

(Enclosures Omitted.]

ID: nht76-4.29

DATE: 10/07/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Pullman Trailmobile

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Trailmobile's August 13, 1976, question whether a trailer would be considered to be newly manufactured for purposes of compliance with applicable safety standards if it is assembled from all new materials except for axles (axle beams, spindles and brakes, and associated brake drums, wheels, seals, and bearings) from an existing trailer whose identity and ownership would be continued in the reassembled trailer.

The answer to this question is yes. The assembly of a trailer entirely from new materials except for the trailer axles does not qualify as a "repair" under NHTSA regulations (49 CFR @ 571.7(f). This regulation states that such trailers will be considered newly manufactured unless, "at a minimum, the trailer running gear assembly (axle(s), wheels, braking, and suspension) is not new . . ." In the case you describe, the suspension would be new.

SINCERELY,

Pullman Trailmobile

August 13, 1976

Office of Chief Counsel National Highway Traffic Safety Administration

RE: Used Components in Trailer Manufacturing NHTSA Regulation @ 571.7(f), Effective July 1, 1976

Opinion is requested concerning the extent to which substitution of new components in trailer running gear assemblies taken from existing trailers is permissible under the above regulation which permits the combination of new and used highway trailer components without the re-assembled trailer being considered "newly manufactured".

A customer has tendered to Pullman Trailmobile 200 trailer running gear assemblies selected by the customer from its inventory of wrecked and damaged van trailers. The customer proposes to ship the assemblies to a Pullman Trailmobile factory, identified by the serial numbers of the existing trailers from which the running gear assemblies were taken. The customer requests Trailmobile to combine such running gear assemblies with new components to complete re-assembled van trailers which will continue to be used by the customer in its transportation business. The trailer running gear assemblies to be shipped to Pullman Trailmobile will consist of the following components:

(a) axle beam including the spindle and brake assembly;

(b) complete axle assembly (including brake drums, wheels, oil seals, bearings, etc.).

All other components of the trailer running gear assemblies have been adjudged by the customer's maintenance employees to require replacement, consistent with safe maintenance and operation practices.

Reference is made to NHTSA's discussion and evaluation of comments upon the proposed regulation published in the July 1, 1976 Federal Register; in particular, to that paragraph reviewing the comments of Firestone Corporation concerning rims and wheels. In that connection, it was stated that "The agency in no way intends to modify safe maintenance and operation practices by its action. Substitution of new components or of use of old components is not advocated or discouraged by this action". NHTSA also reported that "frame attachment components" were excluded from the description of running gear assemblies for fear that persons might reuse damaged attachment hardware.

Based upon the foregoing, a favorable opinion is requested that reuse of the above described components of trailer running gear assemblies in combination with sufficient new running gear and other components required to produce re-assembled van trailers does not result in a "newly manufactured" trailer; assuming, of course, that the re-assembled trailer will be used by the owner of the existing trailer which will continue to be identified by its existing serial number.

If additional facts or information in connection with the agency's determination is necessary or desirable, please call upon this writer for assistance.

Edgar E. Lungren Jr.