2480 Precision Drive, Suite A
Minden, NV 89423
Dear Mr. Yuen:
This responds to your letter, dated October 9, 2009, asking whether the motorcycle rear lamp system you describe is permissible under Federal Motor Vehicle Safety Standard (FMVSS)
No. 108, which governs lamps, reflective devices, and associated equipment on vehicles. I sincerely apologize for the delay in this response. As explained below, we believe that the system would be permissible under FMVSS No. 108.
By way of background, NHTSA is authorized by the Safety Act to issue FMVSSs that set performance requirements for new motor vehicles and new items of motor vehicle equipment. NHTSA does not provide approvals of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture. NHTSA selects a sampling of new vehicles and equipment each year to determine their compliance with applicable FMVSSs. If our testing or examination reveals an apparent noncompliance, we may require the manufacturer to remedy the noncompliance, and may initiate an enforcement proceeding if necessary to ensure that the manufacturer takes appropriate action. NHTSA also investigates safety-related defects.
The following is our interpretation of the Safety Act and the FMVSSs based on the description contained in your letter.
You describe the lamp system as consisting of two lamps, with one lamp located on either side of the rear vertical centerline of the motorcycle. The lamps are separated by a distance of 300 mm (11.8 in). Each of the lamps functions as turn signal, stop lamp, and taillamp. You indicate that the system has four functional modes:
1) Both lamps continuously illuminated as taillamps when the vehicle is on;
2) Both lamps illuminated at a higher intensity as stop lamps when the brakes are applied;
3) One lamp flashing as a turn signal while the other lamp remains continuously illuminated as a taillamp; and
4) In a situation where the brakes are applied at the same time as a turn is indicated, one lamp flashing as a turn signal while the other lamp remains continuously illuminated at a higher intensity.
You also submitted diagrams showing two configurations of this system using lamps with different effective projected luminous lens areas (EPLLA). In the first configuration (No. 1), each of the two lamps has an EPLLA of 25.5 cm2 (3.96 in2). In the second configuration (No. 2), each of the lamps has an EPLLA of 50.3 cm2 (7.8 in2).
You ask whether either of these configurations would be permissible under FMVSS No. 108. In particular, you express concern as to whether the first configuration would meet the EPLLA requirements for a stop lamp because, in Functional Mode No. 4, only one of the two lamps would be illuminated as a stop signal.
As you indicate in your letter, FMVSS No. 108 requires a motorcycle to have one stop lamp but permits it to have two stop lamps symmetrically disposed about the vertical centerline. A motorcycle is also required to have two rear turn signal lamps, one on each side of the vertical centerline, with at least 9 inches separating the lamps. FMVSS No. 108 requires that the stop lamps must meet the requirements of Society of Automotive Engineers (SAE) Standard J586, revised February 1984, and that the rear turn signal lamps must meet the requirements of SAE J588, revised November 1984.
The SAE standards permit the use of multiple compartment lamps or multiple lamps to meet the photometric requirements for stop lamps. The compartments or lamps in such systems are tested together as a unit so long as all the compartments or lamps are within a certain distance of each other. For a two-lamp system, the lamps must be within 560 mm of each other to be tested as a unit.
In previous interpretation letters addressing rear motorcycle lamp configurations, we have applied the distance requirements in the SAE standards to conclude that lamp systems consisting of lamps on either side of the rear vertical centerline can be considered single lamps for the purposes of meeting the stop lamp photometric requirements (See enclosed November 20, 1998 letter to Tadashi Suzuki).
In addition to the requirements contained in the SAE standards, FMVSS No. 108 states that [i]f a multiple compartment lamp or multiple lamps are used to meet the photometric requirements for stop lamps . . . the effective projected luminous lens area of each compartment or lamp shall be at least 22 square centimeters, provided the combined area is at least 50 square centimeters. However, each motorcycle rear turn signal lamp is only required to have an EPLLA of 22.58 cm2 (3.5 in2).
In your letter, the Configuration No. 1 lamp system consists of two lamps located 300 mm (11.8 in) apart, each of which has an EPLLA of 25.5 cm2, for a combined EPLLA of 51 cm2. Accordingly, we believe that this system would meet the EPLLA requirements for a single stop lamp and two motorcycle rear turn signal lamps. In response to your specific question, FMVSS No. 108 explicitly contemplates the optical combination of stop lamps and turn signal lamps. Therefore, we would not consider the stop lamp system to be noncompliant because only one of the lamps would function as a stop signal when a turn signal is flashing. Likewise, we believe
that the Configuration No. 2 lamp system, which consists of two lamps with individual EPLLAs of 50.3 cm2, would meet the EPLLA requirements for two stop lamps and two motorcycle rear turn signal lamps.
However, the Configuration No. 1 lamp system raises another issue that we would like to address regarding the optical combination of the stop lamp and turn signals. The SAE standards state that when a stop lamp is optically combined with a turn signal lamp, the circuit shall be such that the stop signal cannot be turned on if the turn signal is flashing. FMVSS No. 108 adopts the definition of optically combine found in SAE J387, revised November 1987. Under the SAE definition, optical combination results when 1) a lamp has two or more separate light sources, or a single light source that operates in different ways (e.g., a two-filament bulb), and 2) the lamps optically functional lens area is wholly or partially common to two or more lamp functions.
In the Configuration No. 1 lamp system, both lamps together constitute the required single stop lamp, and each individual lamp also acts as a turn signal. Under the definition stated above, the single stop lamp (consisting of both lamps) could be considered to be optically combined with both turn signals. Such an interpretation would mean that Functional Mode No. 4, where one lamp flashes as a turn signal while the other lamp remains continuously illuminated as a stop signal, would not be permissible. Neither of the lamps could be illuminated as a stop signal if one of the turn signals is flashing. In other words, the vehicle would display no signal indicating that the brakes were being applied in such a situation.
In light of these consequences, we do not believe that such an interpretation of the term optically combine is appropriate for the unique situation presented by the lamp system you describe. Instead, we conclude that Functional Mode No. 4 is permissible under FMVSS No. 108. In that mode, the lamp that is flashing as a turn signal ceases operating as a stop signal. Nevertheless, the lamp system would continue to signal when the brakes are applied because the other lamp continues to operate as a stop signal. We caution that this interpretation is limited to the unique motorcycle rear lamp system described in your letter.
I hope this information is helpful. If you have further questions, please contact William Shakely of my staff at (202) 366-2992.
O. Kevin Vincent
Enclosureref: Standard No. 108