Originally Posted By: David_g
I quoted the section on the California Vehicle Code that allows brake light flashers. You're welcome to tell the that they may not do that. I'm sure we're not the only state that allows them.
I'm sure you're right. And those states' permissiveness would be as null and void as California's.
From FMVSS 108 (
https://www.ecfr.gov/cgi-bin/text-idx?node=se49.6.571_1108):
S4
Definitions
Stop lamps are lamps giving a
steady light to the rear of a vehicle to indicate a vehicle is stopping or diminishing speed by braking.
Also see Table I-a - Required Lamps and Reflective Devices
Stop lamps -
Steady burning. Must be activated upon application of the service brakes.
Since flashing is not 'steady burning', there is no allowance in FMVSS 108 for flashing stop lamps (brake lights). Thus California Vehicle Code 25251.5.c is in direct conflict.
Federal laws and regulations trump state laws and regulations when there is a conflict. (Google: federal preemption)
Specific cite: 49 U.S. Code 30103(b)(1) (
https://www.law.cornell.edu/uscode/text/49/30103)
'Preemption — When a motor vehicle safety standard is in effect under this chapter (301 - Motor Vehicle Safety), a State or a political subdivision of a State may prescribe or continue in effect a standard applicable to the same aspect of performance of a motor vehicle or motor vehicle equipment
only if the standard is identical to the standard prescribed under this chapter. '
So, to sum up flashing brake lights:
Illegal in the U.S.? Yes, regardless of what your state says.*
A good idea? Maybe.
Will a NHTSA SWAT team hunt you down for having one? Probably not.
* - I believe the lighting behavior on emergency vehicles is not federally regulated so the state/local authorities have full control over what is allowed