David Robertson, Manager
Environmental and Safety Engineering
Mazda North American Operations
1500 Enterprise Drive
Allen Park, MI 48101-2053
Dear Mr. Robertson:
This responds to your request asking whether a driver and passenger seat belt reminder system under development by Mazda would violate any Federal motor vehicle safety standards (FMVSS). Our understanding of the Mazda system, based on a meeting between staff from the National Highway Traffic Safety Administration (NHTSA) and Mazda, is that the contemplated system is designed to meet the new European New Car Assessment Program criteria for belt minders. The Mazda system, as described, is not prohibited by any FMVSS.
According to your letter, the Mazda system would consist of a reminder system that would trigger if either the driver or front passenger fails to buckle his or her seat belt by the time the vehicle reaches a forward speed of 20 km/h (12.5 mph). The reminder will not sound when the vehicle transmission is in reverse. Once triggered, the reminder system will produce an audible warning signal that will continue for 90 seconds or until the seat belts are fastened, whichever occurs first. This audible signal is indistinguishable in tone from the warning signal used by Mazda to meet the mandatory seat belt warning system required by S7.3 of FMVSS No. 208, Occupant crash protection. S7.3 of that standard requires the driver's seating position to be equipped with a seat belt warning system that activates, under specified circumstances when the seat belt is not buckled, a continuous or intermittent audible signal for a period of "not less than 4 seconds and not more than 8 seconds," and a continuous or flashing warning light for not less than 60 seconds after the ignition switch is turned on.
The prohibition on any audible signal lasting longer than 8 seconds reflects a statutory requirement imposed by Congress in response to public resistance to seat belt interlock systems.  49 U.S.C. 30124 provides, in relevant part, that a motor vehicle safety standard "may not require or allow a manufacturer to comply with the standard
By using...a buzzer designed to indicate a safety belt is not in use, except a buzzer that operates only during the 8-second period after the ignition is turned to the 'start' or 'on' position."
While the statute prohibits NHTSA from requiring, or specifying as a compliance option, an audible seat belt warning that sounds outside of the specified 8-second period, it does not prohibit vehicle manufacturers from placing such systems in their vehicles. However, given FMVSS No. 208's requirement that the required seat belt warning be no longer than 8 seconds, a vehicle manufacturer wishing to provide a voluntary audible signal must provide some means of differentiating the voluntarily provided signal from the required signal. Differentiation is required so that NHTSA can definitively determine whether the warning signal meets the requirements of the standard in a compliance test.
One way to differentiate between the two signals is to utilize different sounds for each warning signal. The Mazda system, as contemplated, would not do this. Another way to differentiate between the two signals is a clearly distinguishable lapse in time between the two signals. While generally speaking, the Mazda system would provide a distinguishable lapse in time, there are instances where there may not be such a lapse under real world operating conditions.
According to your letter, the warning signal used by Mazda to meet the requirements of FMVSS No. 208 continues for six seconds from the time the ignition is turned on or until the driver's seat belt has been engaged, while the non-mandatory belt reminder system would trigger once the vehicle had reached a forward speed of approximately 12.5 mph. Under most circumstances, it is unlikely that this 12.5 mph forward speed would occur within six seconds of engaging the ignition. However, in some circumstances it would be possible to achieve this speed quickly enough to preclude a vehicle occupant from distinguishing between the two, separate warning signals.
Nevertheless, we have determined that the Mazda system would not violate S7.3 of FMVSS No. 208. The fact that, under limited circumstances, a particular vehicle occupant may be unable to distinguish between the two warning signals is not determinative. As noted above, the distinction between the two signals is needed to determine whether the mandatory signal complies with FMVSS No. 208. The Mazda system, as contemplated, will comply with S7.3 when tested in accordance with the applicable laboratory test procedure for FMVSS No. 208, TP208-12. Under that test procedure, the transmission is never moved from "park" once the ignition is engaged. Accordingly, the second, voluntary warning signal will not sound because it is only engaged once the vehicle achieves a particular forward speed. Accordingly, the system will not prevent NHTSA from clearly determining whether the requirements of S7.3 have been met.
I hope this information addresses your concerns. If you have any further questions, please feel free to contact Rebecca MacPherson of my staff at (202) 366-2992.
See H.R. Rep. No. 93-1452 (to accompany S355), at pp. 44-45 (1974), reprinted in 1974 U.S.C.C.A.N. 6108.