Interpretation ID: nht76-2.26

DATE: 10/07/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Wesbar Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of September 7, 1976, asking several questions concerning paragraph S4.4.1 of Federal Motor Vehicle Safety Standard No. 108. I am sorry that we were unable to respond by September 29 as you requested. Your questions and our answers are as follows:

"1. What is the DOT specific definition and interpretation of the words 'combined optically' as they appear in paragraph S4.4.1 of DOT 108?"

In pertinent part, S4.4.1 states that "no clearance lamp may be combined optically with any taillamp." The phrase "combined optically" as used here means that the luminous area of a lens used for a taillamp may not be also used as the luminous area of a lens for a clearance lamp. In other words lamps are "combined optically" when the same luminous area of a lens is lighted for more than a single function.

"2. Can a clearance lamp and tail lamp be combined in a single compartment with no opaque barrier wall existing between the clearance lamp bulb and the tail lamp bulb?"

The answer is no because the same luminous area of the lens would be lighted when both lamps are in use, and the lamps would be "combined optically."

"3. Does the DOT have no objection to a flashing red signal issuing from the side (at right angles to the fore-aft center line of the trailer) of the clearance lamp?"

Generally S4.6(b) requires most vehicle lamps to be steady burning in normal operation. If the right angle lamp serves as the rear side marker lamp, however, S4.6(b) allows it to be flashed for signaling.

"4. What is the DOT specific definition and interpretation of the term 'clearance lamp' as it is used in DOT 108?"

The term "clearance lamps" is defined by SAE Standard J592e, incorporated by reference in Standard No. 108, and are "lamps which show to the front or rear of a vehicle . . . to indicate the overall width and height of the vehicle."

"5. Does the 'clearance lamp' as the words are used in DOT 108 indicate a lamp intended to serve as its major function, a back up lamp in the event of failure of the tail light filament in the combination tail, turn and stop light bulb."

There is no intent that a clearance lamp serve as a backup lamp in the event of a taillamp filament failure though obviously both lamps perform a marking function.

"6. If DOT approves the combination of a clearance lamp and tail lamp in the same compartment, would it also approve for a boat trailer, moving the tail light outboard to show the extreme width of an over 80" vehicle and eliminate the need for a clearance lamp under those circumstances."

The question is moot since a combination clearance lamp-taillamp is not permitted.

I understand that you discussed the photometric test procedure for optically combined lamps with Mr. Owen of this agency, by telephone on September 22, 1976. So that there may be no misunderstanding I would like to set forth the test procedure in this letter. If a single lamp bulb (or filament) is used in the combined lamp, the photometrics for all of the functions must be met simultaneously. If two or more lamp bulbs (or filaments) are used and each is to provide a separate function, only those which provide that function are to be energized during the photometric test. Therefore, in a multiple compartment side marker and clearance lamp (or a multiple compartment tail and clearance lamp that is not optically combined), the clearance lamp bulb is not energized during the photometric test for the other function, and vice versa.

I hope this answers your questions.

SINCERELY,

WESBAR CORPORATION

September 7, 1976

Frank Berndt Acting Chief Counsel U.S. Dept. of Transportation National Highway Traffic Safety Administration

Refer: DOT 108, paragraph S4.4.1

On June 9, 1975 your predecessor in office answered an inquiry we made relative to a light design, and the last paragraph of his letter stated in part:

"Since the clearance lamp and tail lamp are in separate compartments and not optically combined -- the lamp design does not violate S4.4.1."

We have recently seen two lamps which bear the letters "DOT", in each of which the clearance, tail light and turn signal bulbs are all in the same compartment, i.e. the clearance lamp is not in a separate compartment.

It has always been the opinion of the writer and of boat trailer manufacturers, that in order to comply with S4.4.1, the clearance lamp would have to be in a compartment separated from the tail and stop lamp. However, while we were in Washington last week visiting your compliance office, we were advised that a Mr. Lou Owen had given a verbal interpretation of S4.4.1 in which he gave approval for the tail and clearance lamp to be in a single compartment, with no separating wall between them.

It would seem logical that tail lamp and clearance lamp should be separately compartmented. If the bulbs were in the same compartment with no shielding between them, the stop and turn light would illuminate that section of the compartment intended as a clearance lamp area, and at times the clearance lamp would appear to be flashing as well as varying in intensity. This would make for a confusing and hazardous situation for a driver traveling some distance behind a trailer equipped with such a combination lamp.

If this verbal interpretation which approves having the two lamp bulb mounted in the same compartment without a separating wall is valid, why should there be any need for a clearance lamp on a boat trailer since the tail lights could be mounted sufficiently outboard so they would indicate, when lighted, the overall width of the trailer?

We would appreciate receiving the DOT's specific interpretation of the words "combined optically". In its usual context, the words "combined optically" would mean a combination of light source and lens, and applied to S4.4.1 would seem to indicate that, in fact, the clearance lamp would have to be separately compartmented from the tail, stop, turn, and hazard lamp compartment.

When the clearance and tail lamp are housed in the same compartment there is a definite impairment of the combination turn, stop and hazard function of the lamp and an unsafe and confusing situation exists. We can report to you that while conducting an actual night test at a country road intersection, when a trailer was approaching the intersection with turn signal bulb flashing in the uncompartmented tail light, at 150 feet distance it was difficult to tell if the trailer ahead was on the same course as the following vehicle or crossing ahead of it at right angles.

While we were at the compliance section office, we were appalled to hear an interpretation of the term "clearance light" to the effect that the clearance lamp was not necessarily a separate lamp but was intended as a "back-up" light in the event the tail light filament should fail.

We have never ever heard or had it intimated to us that such was the purpose of a clearance lamp and we don't believe that it was ever intended to be so defined. When you consider the fact that the lamp on a semi trailer is at the uppermost corner of the trailer body (a long distance from the tail lamp!), and that travel trailers, buses and other vehicles also have the clearance lamp at the top extreme corners of the vehicles, it is difficult to conceive of their application as being a back up substitute for a defective tail lamp.

Carrying our argument further, on a trailer of less than 80" in width NO clearance lamp is required but the possibility of failure of the tail lamp filament is just as great. What then is supposed to serve as "back up" lamp for it? It is our observation that someone was just not thinking when he made the statement that a clearance lamp is really only there to serve as a "back up" lamp for the tail light.

In summary we ask for your specific answers to the following:

1. What is the DOT specific definition and interpretation of the words "combined optically" as they appear in paragraph S4.4.1 of DOT 108?

2. Can a clearance lamp and tail lamp be combined in a single compartment with no opaque barrier wall existing between the clearance lamp bulb and the tail lamp bulb?

3. Does the DOT have no objection to a flashing red signal issuing from the side (at right angles to the fore-aft center line of the trailer) of the clearance lamp?

4. What is the DOT specific definition and interpretation of the term "clearance lamp" as it is used in DOT 108?

5. Does the "clearance lamp" as the words are used in DOT 108 indicate a lamp intended to serve as its major function, a back up lamp in the event of failure of the tail light filament in the combination tail, turn and stop light bulb.

6. If DOT approves the combination of a clearance lamp and tail lamp in the same compartment, would it also approve for a boat trailer, moving the tail light outboard to show the extreme width of an over 80" vehicle and eliminate the need for a clearance lamp under those circumstances.

On September 29, 1976 there will be a meeting of the Trailer Manufacturers Association. In attendance will be representatives of all major manufacturers of boat trailers. We would appreciate your expediting your replies to the six questions posed above in order that we may give a copy of them to the group attending that meeting.

Since your interpretation of the questions given in this letter are of such vital importance to the boat trailer manufacturer, dealer and consumer, we would be most grateful for your clear, concise answers.

For your ready reference we attach copies of our previous correspondence and the reply we received. We also submit for your study, photos of a typical lamp where tail lamp and clearance lamp are combined in one compartment.

Looking forward to receiving your prompt response, we remain.

B. R. Weber Executive Vice President

cc: SEN. WILLIAM PROXMIRE; SEN. GAYLORD NELSON; REP. WILLIAM A. STEIGER