Mr. Michael J. Rood
Vice President, Engineering
Safe-Lite Mfg. Co.
6230 Gross Point Road
Niles, IL 60714

Dear Mr. Rood:

This is in reply to your letter of July 23, 1997, to Taylor Vinson of this Office, asking for an interpretation of Federal Motor Vehicle Safety Standard No. 108. We apologize for the delay in responding, but your letter presented unique questions which took some time to resolve to the agency's satisfaction.

There are three aspects of reflex reflector conspicuity treatment that you wish us to address, to clarify questions asked by owners who wish to retrofit their trailers, as well as by manufacturers of new trailers. Retrofitting of trailers manufactured before December 1, 1993, of course, is not subject to the requirements of Standard No. 108.

As you point out, S5.7.2.2(a) allows the use of reflex reflectors as a conspicuity alternative to S5.7.1.4 "in the same locations and in the same length in which retroreflective sheeting is required. . . ." You believe that because reflex reflectors cannot be trimmed, it is impossible that reflex reflectors can comply in some instances with the literal requirement of S5.7.2.2 that they be applied "in the same length" as retroreflective sheeting to meet conspicuity requirements.

The conspicuity requirements of Standard No. 108, including the provisions referring to practicability, are stated in terms of sheeting material. Each reflex reflector used to fulfill conspicuity requirements must have photometric performance equivalent to that of a 100 mm length of sheeting material, and the conspicuity treatment may then be implemented using reflex reflectors with a center-to-center spacing not greater than 100 mm. Conspicuity treatments using one reflex reflector as an alternative to 100 mm of sheeting material would be equivalent in minimum performance and nearly identical in reflective appearance to a treatment using sheeting material.

The trailer manufacturer has the choice of using either reflex reflectors or sheeting material. However, reflex reflectors could not be used to comply with the standard if they cannot replicate a complying sheeting material installation. For example, S5. requires the conspicuity treatment to originate and terminate "as close to the front and rear as practicable," and that it need not be continuous as long as "the spaces are distributed as evenly as practicable." If sheeting material would terminate closer to the front or rear than is possible with reflex reflectors on a particular trailer, or if it results in a more even distribution of spaces, then sheeting material must be used to meet the practicability provisions. There may be instances when sheeting material is better than reflex reflectors in taking account of ribs and obstructions on the trailer body in marking the overall length of the vehicle, or when its use would result in lesser gaps in the treatment than use of reflex reflectors.

Similarly, if a trailer manufacturer determines that it may use reflex reflectors as a conspicuity treatment, it must use a single reflector of 100 mm length rather than a bar of reflectors of 300 mm if the single reflector would more closely mark the extreme width or length of the trailer or result in smaller gaps.

Underride Protection Devices

Paragraph S5. requires a strip of retroreflective sheeting in alternating colors to be installed across the full width of the horizontal member of the rear underride protection device.

You have enclosed sample reflex reflector bars that are 12 inches (approximately 300 mm) in length. You point out that, unlike retroreflective sheeting, reflex reflectors cannot be trimmed in application. Assuming that the underride protection bar is 90 inches (7' 6") in length, you present two options. In the first option, you would center a white reflex reflector on the bar, and work outward with alternating red and white reflectors (seven in all), which would leave 3 inches of uncovered surface at both ends of the underride bar. In the second option, you would work inward from reflectors placed at the end of the underride bar, distributing the 6 inches of uncovered surface evenly between reflectors. We understand that this means that seven reflectors would be provided, with only 1 inch of space between adjacent reflectors.

The standard requires reflex reflectors to be used "in the same locations and in the same length in which retroreflective sheeting is required...with the center of each reflector not more than 100 mm (4 in) from the center of each adjacent reflector." The underride protection device in question would have been treated with 90 inches of sheeting material, and an exact replacement using reflex reflectors would require 22 reflex reflectors with each reflector replacing 4 inches of sheeting material. However, Standard No. 108 does not recognize fractional reflex reflectors because, unlike sheeting material, they are non-homogenous indivisible units. Nor does it assume that there will be sufficient space to apply a greater number of whole reflex reflectors. Therefore, the agency has decided that the "full width" requirement can be met by using the greatest number of whole reflectors (on a basis of one reflector per 4 inches) that will fit in the length required for sheeting material. Since both of the options you propose use 21 rather than 22 reflex reflectors, neither would satisfy the standard. Given the space limitations on an underride guard, you would have to supplement the bars of three reflectors with some double or single reflectors to achieve acceptable coverage. Since the maximum cumulative space between reflectors would always be less than 4 inches per element of the conspicuity treatment, the distribution of spaces would have little practical significance. However, arrangements that mark the actual full width are always preferable to those that only approximate it.

Rear Width of a Trailer

Similarly, the conspicuity treatment specified in S5. is to be applied "across the full width of the trailer." You ask how a continuous pattern of alternating red and white reflex reflectors are to be applied in multiples of 12-inch segments when there are rear door hardware obstructions that do not allow it.

You suggest that if the linear space between hardware obstructions is between 12 and 24 inches, then one reflex reflector can be centered in this space provided that it is a different color than its two neighbors. If the space is between 24 and 36 inches, two reflex reflectors could be centered, again preserving a pattern of alternating colors. This scheme would apply in successive 12-inch increments with the reflectors applied at both ends of the completed scheme, "positioned as close to each end as practicable."

As in the underride interpretation above, the minimum number of reflex reflectors needed to implement an element of conspicuity treatment is the number of mm (or inches) of sheeting material that would have been used, divided by 100 mm (or 4 inches) and rounded down to the greatest whole number. In general, it would be a matter of chance if the minimum number of reflex reflectors could be arranged in a single line when obstructions are present, especially when the reflectors are combined in bars of three. However, element 1 of the rear trailer conspicuity treatment (S5. is not required to be located on the same parallel plane; obstructions can be cleared by mounting some of the reflex reflector bars above or below obstructions to obtain a greater number of reflex reflectors in the treatment. Of course, the treatment must mark the full width of the body in the same manner as a treatment with sheeting material.

Unique Trailer Side Walls and Rub Rails

The required conspicuity treatment for trailer sides is set forth in S5. It requires that conspicuity treatment originate and terminate as close to the front and rear as practicable, and that a strip of retroreflective sheeting need not be continuous as long as not less than half of the length of the trailer is covered and the spaces are distributed as evenly as practicable.

You bring to our attention the fact that the distance from one outer rib to another on the side of some "plate" trailers could vary from 5 to 42 inches, and that your reflector will not fit into a section narrower than 12 inches. You would provide reflex reflectors in alternate color segments to cover not less than half the trailer length, even though there might be a space between some segments. This treatment would start and finish as close to both ends of the trailer "as practicable," and meet the requirement of S5.7.1.3(c) that neither color in the aggregate exceed two-thirds of the total provided to mark the sides.

As noted above, the practicability requirements for the placement and distribution of the retroreflective material in S5. were conceived and expressed in terms of a treatment using sheeting. If these requirements are more closely fulfilled using sheeting material, then sheeting material must be used. Although either sheeting material or reflex reflectors could be used on trailers with uninterrupted sills, it may be impossible to use triple reflector bars exclusively as a complying conspicuity treatment on the side of a trailer with ribs. Depending on the distance between the ribs, trailer manufacturers would be expected to use single reflectors or bars of two reflectors (or simply to use sheeting material) for that element of the conspicuity treatment.

If you have further questions, you may phone Taylor Vinson at 202-366-5263.

John Womack
Acting Chief Counsel