Headlight flashing is the act of a driver flashing their headlights at an oncoming driver by briefly turning the headlights on or off, or from high beam to low beam, or low beam to high beam. There is no set or clear message transmitted by headlight flashing, but it often means the driver who flashes their headlights believes the oncoming driver’s headlights are inappropriately on high beams or are not turned on or illuminated when they should be.

Headlight flashing may also be intended to convey other messages, such as warning another driver of the flashing driver’s presence; telling another driver to proceed in front of the flashing driver (yielding the right of way); or warning an oncoming driver of danger ahead—which may include a deer or other animal in the road, an automobile wreck, or a police officer hidden from view who is checking the speed of passing drivers and issuing speeding tickets (a speed trap).

Police officers have sometimes issued traffic tickets to drivers for headlight flashing, and in some instances a traffic stop for headlight flashing has led to more serious charges and an arrest for DUI/DWI, for example. Tickets for headlight flashing are often issued based on an alleged violation of a municipal ordinance or a state statute that prohibits:

• high beam headlights within a certain distance (500 feet, for example) of an oncoming driver;

• aggressive driving;

• having flashing lights on a vehicle; or

• obstructing a police investigation.

Drivers who have received tickets for headlight flashing have sometimes challenged the ticket—or the traffic stop that led to an arrest and additional charges—on the ground that headlight flashing is a communication protected by the First Amendment to the United States Constitution.

Laws and ordinances vary from state to state and among cities and towns (municipalities), and state and federal courts have arrived at different conclusions when applying the First Amendment and other laws and ordinances to traffic tickets or stops based on headlight flashing.

In Wisconsin, headlight flashing is not explicitly regulated by a specific state statute that addresses the act of flashing headlights to communicate with other drivers. However, Wisconsin does have laws regarding the appropriate use of headlights. For instance, Wisconsin Statute 347.12(1) requires that headlights must be dimmed when approaching or following another vehicle within 500 feet. While headlight flashing could potentially be interpreted as a violation of this statute if it's done within the specified distance, the act itself is not directly prohibited. Additionally, Wisconsin Statute 347.12(2) and (3) prohibit the use of flashing or rotating lights that are blue, red, or white, as these are reserved for emergency and certain service vehicles. As for the First Amendment defense, while some courts in other jurisdictions have recognized headlight flashing as a form of protected speech, Wisconsin courts have not definitively ruled on this issue. Therefore, while headlight flashing is not outright illegal in Wisconsin, it could lead to a citation under certain circumstances, such as misuse of high beams or if it's interpreted as aggressive driving. Drivers should exercise caution and consider the potential for misinterpretation by law enforcement when using headlight flashing as a means of communication.