"After many of the delays that auto-makers love, on August 15, 1973,
Department of Transportation officials finally issued a new regulation
requiring ignition interlocks on all new cars. There was now no need for
airbags, so they dropped from the picture. During this two-year delay,
however, Congress member Louis Wyman (R-N.H.) was preparing an amendment
to the Motor Vehicle and School Bus Safety Act of 1974, which said,
"Federal safety standards may not require that any vehicles be equipped
with a safety belt interlock system." Some Hill staffers say Ford actually
wrote the amendment. With a well-timed push from auto lobbyists, the
amendment passed. The airbag and the ignition interlock were now both
dead, victims of one of the most brilliantly executed double fixes in the
history of lobbying."

____________________________________________________________

We note that our agency's previous experience with ignition interlocks
indicates that great care must be taken in requiring vehicle modifications
to induce higher belt use, to avoid consumer backlash. As of August 1973,
Standard No. 208 required all new cars to be equipped either with
automatic protection or an ignition interlock for both front outboard
seating positions. General Motors sold about ten thousand of its 1974
model year cars equipped with air bags that met the automatic protection
requirement. Every other 1974 model year car sold in the United States
came with an ignition interlock, which prevented the engine from operating
if either the driver or front seat outboard passenger failed to fasten
their manual seat belt.

   In a notice published in the Federal Register (39 FR 10272) on March
   19, 1974, we described the public reaction to the ignition interlock
   as follows: "Public resistance to the belt-starter interlock system .
   . . has been substantial, with current tallies of proper lap-shoulder
   belt usage on 1974 models running at or below the 60% level. Even that
   figure is probably optimistic as a measure of results to be achieved,
   in light of the likelihood that as time passes the awareness that the
   forcing systems can be disabled, and the means for doing so will
   become more widely disseminated. . . ."

   There were also speeches on the floor of both houses of Congress
   expressing the public's anger at the interlock requirement. On October
   27, 1974, President Ford signed into law a bill that prohibited any
   Federal motor vehicle safety standard from requiring or permitting as
   a means of compliance any seat belt interlock system. In response to
   this change in the law, we published a final rule in the Federal
   Register (39 FR 38380) on October 31, 1974 that deleted the interlock
   option from Standard No. 208 effective immediately.

________________________________________________________________

   DOT gave manufacturers a further choice for new vehicles manufactured
   between 1972 and August 1975. Manufacturers could either install a
   passive restraint device such as automatic seatbelts or airbags or
   retain manual belts and add an “ignition interlock” device that in
   effect forced occupants to buckle up by preventing the ignition
   otherwise from turning on. 37 Fed. Reg. 3911 (1972). The interlock
   soon became popular with manufacturers. And in 1974, when the agency
   approved the use of detachable automatic seatbelts, it conditioned
   that approval by providing that such systems must include an interlock
   system and a continuous warning buzzer to encourage reattachment of
   the belt. 39 Fed. Reg. 14593. But the interlock and buzzer devices
   were most unpopular with the public. And Congress, responding to
   public pressure, passed a law that forbade DOT from requiring, or
   permitting compliance by means of, such devices. Motor Vehicle and
   Schoolbus Safety Amendments of 1974, §109, 88 Stat. 1482 (previously
   codified at 15 U.S.C. § 1410b(b) (1988 ed.)).

so there...