Discordant horn sounds can affect driver safety

Photo credit: Mike Bird

by Jeanine Botta, MPH, Co-founder, The Quiet Coalition

In a recent News Tribune “Rules of the Road” column, a reader asked if using a horn to signify that a car is locked is considered misuse of vehicle safety equipment. The reader described their tendency to ignore horn honking because of the assumption that it means someone is locking a car. Columnist Doug Dahl, who is the director of communications for the Washington Traffic Safety Commission, disagreed with the reader.

Dahl challenged the reader’s statement about tuning out horn honks because of their prevalence as a possible lock signal. “If you’re driving through an intersection and you hear a horn blaring, I bet you don’t ‘figure it’s someone parking their car,’” he said. Dahl seems to assume that the reader’s context was for cars not on the road.

He references a Washington State law on vehicle horn regulations to defend his argument that horns can be used when a car is parked or not being driven. “When you’re on the road, your horn is to be used only as a warning device. Once you’re parked though, the limits on how you can use your horn no longer apply, at least based on this law,” Dahl wrote.

The section he refers to states, “The driver of a motor vehicle shall, when reasonably necessary to insure safe operation, give audible warning with his or her horn but shall not otherwise use such horn when upon a highway.” The phrase “when upon a highway” means “when driving” and in vehicle legislative terminology, the word “highway” refers to any road, street or area where cars are driven. Dahl reasons that because the law says drivers should use the horn in a limited way when driving, once they are not driving, the law does not apply. He offers no further argument that his interpretation of the law is accurate.

By contrast, a recent court decision out of California, that was later upheld by the Supreme Court, uses similar state laws to argue that horn use is limited to warning of imminent danger. It does not offer exceptions. 

Complaints about horn-based lock alerts include off-the-road experiences, like being awakened from sleep, walking near a remotely locked car emitting a loud honk and difficulty concentrating in settings that face street parking. But Dahl is wrong to assume horn lock signals couldn’t confuse drivers or threaten safety on the road. 

In 2012, I started researching impacts of horn-based lock alerts. I interviewed people in the United States and Canada, and presented my research findings at the International Congress on Acoustics 2013 in Montreal. Many people cited impacts that occurred while they were at home or outside, but not driving. Others described confusing signals while they were driving through parking lots, where sudden horn honks caused them to panic, jamming on the brakes. 

Cyclists described instinctively swerving when passing parked cars with remotely activated horns. My father described pulling into a driveway just as a parked car emitted a horn sound. Perceiving it as a warning, he acted instinctively, speeding up and scraping the side of the car against a stone wall. He realized too late that someone had just been locking a car.

A discordant horn honk can elicit an instinctive physical response whether you are asleep or falling asleep, on the road, driving or cycling. Discordant horn sounds can affect driver safety. For this reason, horn sounds should not be used to reflect the lock status of a parked car.

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