From bizpacreview.com:
Hey flashers, you are now protected under the First Amendment right to free speech to give the universal sign to fellow drivers that cops are nearby running radar.
Hailed as a “victory for drivers,” U.S. District Court Judge Henry Autrey in St. Louis, Mo. ruled Monday that flashing one’s headlights to warn others about speed traps was free speech.
This is an interesting question I'd never thought of before. I haven't read the court's ruling (it's not linked on the page above), but the result seems right to me.
As far as I know, flashing one's headlights in and of itself is not illegal in any state. Drivers flash their headlights for any number of purposes, sometimes in lieu of or in tandem with honking the horn, to signal other drivers. One could call it a safety feature.
Is flashing one's headlights to signal other drivers that a speed trap is nearby the kind of expression that is protected by the First Amendment? Clearly it is; it's communicative and conveys a particularized message. It's expressive conduct under United States v. O'Brien, 391 U.S. 367 (1968).
Of course that's not the end of the inquiry; the next question is, does the state have a justification for banning it? It can't reasonably be argued that this would be a content-neutral time/place/manner restriction, because it's not content-neutral; it's specifically directed at suppressing a very specific expression of a very specific idea: "Dude, speed trap, slow down." [OK, maybe not that precisely...]
Let's stipulate for a moment that promoting highway safety is a compelling governmental interest to which a law banning speed-trap-headlight-flashing-warnings would be directed. Is the law narrowly tailored to serve that interest?
Here's where the conversation gets interesting. The state endeavours to promote and maintain highway safety by setting speed limits and sending state troopers out onto the highway to catch speeders and give them tickets. When drivers flash their lights to warn other drivers of speed traps, it helps those other drivers avoid getting a ticket for speeding, thus (theoretically) helping them avoid getting caught breaking the law. It makes it harder for the state trooper to do his job. And state troopers can't be everywhere at once, so they need to catch speeders speeding when they speed past speed traps.
But hold on: You can't assume that everyone who saw a speed-trap warning signal and drove past the speed trap at 54 MPH was necessarily speeding when he saw the signal, let alone at any other time. You also can't assume that the driver who sent the signal knows how fast the other drivers are going as they approach the speed trap, or even that he sent the signal because he thought or assumed they were speeding. So the driver flashing his lights is not necessarily encouraging other drivers to break the law, or even to avoid getting caught.
More importantly, as ACLU attorney Tony Rothert is quoted in the article as saying, "it’s also good for the public because it tells people to slow down, to use caution. That’s never a bad thing[.]" The worst thing that can happen when a driver flashes his lights to warn of a speed trap, is that another driver who is speeding will slow down enough, long enough, to avoid getting a ticket, and then accelerate again until he sees another warning. Or gets a ticket. Or not. The alternative would be to require drivers to simply let speeders speed, just so they can be ticketed.
The fact is that speeders are always at risk of being ticketed whether other drivers warn them or not. And such warnings are not necessarily to be expected when you're out on the road. So allowing drivers to signal speed trap warnings to other drivers doesn't materially increase the risk of speed-related harm. Remember, the goal is to promote highway safety, and that goal is better accomplished by getting people to slow down than by making sure they get a speeding ticket. In that sense, flashing headlights to warn of speed traps helps the police more than it hurts them.
One more thing: It's important to note again that the purpose of speed limits and speed traps is to get people to slow down and drive at or below the speed limit, not to issue tickets or to raise revenue for the state. Allowing speed-trap warnings might interfere with the latter interest, but not the former.
Ultimately, speed-trap warning signals by drivers don't make the roads less safe. Banning speed-trap warning signals by drivers would not make them safer. Accordingly such a law would not be narrowly tailored to the admittedly compelling state interest in highway safety.
It'll be interesting to see if this ruling is appealed, and what happens from here. But I think the court got this one right. What does everyone else think?