Motorists sometimes flash their headlights to alert other drivers to a road hazard or approaching auto accident.

No Colorado Law Bans the Practice

Since the 1970s, headlight flashing has been a common means of driver-to-driver communication in many areas of the world, including in the U.S., where some states believe that drivers have a right under the First Amendment to flash their headlights, but in other states, it is against the law.

Headlight flashing, also known as an optical horn, is a driver’s way to attract attention. Motorists might flash their headlights at another driver for any number of reasons, such as to:

  • Let another driver know they are there.
  • Respond to another’s driver’s actions.
  • Indicate that one driver is yielding the right of way to another, e.g. to let them merge into traffic.
  • Alert other drivers to a road hazard or approaching auto accident.
  • Inform another motorist that his headlights are misaligned, burned out, or not turned on (or that they are on, and should not be).
  • Signal an intention to pass another driver.
  • Request that a leading driver speed up or change lanes to get out of the way of a faster moving vehicle.
  • Warn other motorists of the presence of police in the area.

In 2014, a federal court ruled that flashing one’s headlights was a constitutionally protected form of speech when it issued a permanent injunction prohibiting the Ellisville, Missouri Police Department from citing drivers who flash their lights to warn other motorists of the presence of radar or speed traps.

Headlight flashing is illegal in several states, however, including Alaska, Arizona, Illinois, Louisiana, Maryland, Michigan, and North Dakota. Other states treat the practice differently:

  • In California, it is legal for a driver to flash their headlights to indicate their intention to pass on a road where passing on the right is legal, but headlight flashing on a multiple-lane highway is against the law.
  • Colorado has no specific law against headlight flashing.
  • Headlight flashing is protected under the First Amendment in Florida and Tennessee.
  • A flashing to warn citation was successfully defended in Illinois in 2015, making the practice illegal.
  • Massachusetts does not technically forbid headlight flashing, but law enforcement is allowed to ask a motorist if they were flashing their lights to warn oncoming motorists of police presence and if they deny this, the officer can ask if the vehicle’s lights are defective, which is illegal.
  • In Minnesota, motorists can briefly flash their high beams in a manner “that does not blind or impair approaching drivers.”
  • New Jersey drivers can legally flash their lights to warn approaching drivers of speed traps ahead.
  • In New York, headlight flashing is not illegal, as long as “dazzling lights” do not “interfere with the driving of approaching vehicles.”
  • Ohio courts have ruled that flashing headlights to alert approaching drivers to a radar trap does not constitute obstructing a police officer from performing their duties.
  • According to the Oregon Constitution, flashing a vehicle’s headlights to warn others of law enforcement presence is protected free speech.
  • Driving with high beams within 500 feet of oncoming traffic or 300 feet of traffic in front of the driver is illegal in Washington.
  • In Wisconsin, a driver is allowed to intermittently flash their high beams at an oncoming vehicle whose high beams are lit.

Although headlight flashing is widely practiced, many consider it to have vague and contradictory meanings. According to a 1992 Japanese study, “car drivers are no better at communicating with each other than the average insect.”

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