What it means
The Stupid Motorist Law is Arizona’s name for the moment a driver decides the barricade does not apply to them. The statute behind it, ARS 28-910, says that a driver who takes a vehicle onto a public road temporarily covered by a rise in water, where the road has been barricaded because of flooding, is liable for the cost of the emergency response that follows. The bill can run to $2,000.
Nobody in Arizona says “ARS 28-910.” Everyone says the nickname, usually in July and August, usually while watching helicopter footage of an SUV in a brown torrent with someone sitting on its roof. It is half a legal reference and half a judgment, and it is one of the few laws most residents can describe accurately.
The practical side of monsoon driving, from dust walls to flooded underpasses, is in the monsoon field manual. This page is about the law and its name.
Where you’ll meet it
On television every monsoon, on social media under rescue photos, in safety briefings from fire departments, and on the road signs at dip crossings in the north, where “Do Not Enter When Flooded” is the polite version of the same message.
Where the word came from
The law dates to 1995, when legislators frustrated by drivers ignoring posted warnings, and by the cost and danger of pulling them out of washes, wrote the cost of the rescue back onto the driver. The text is dry: “emergency response expenses,” “public agency,” “reasonable costs directly incurred.” The nickname is not in it.
Who first called it the Stupid Motorist Law is unknown. No legislator, reporter or official has claimed it, and the phrase was already standard in news coverage by the time anyone thought to ask. It stuck because it is accurate and because Arizona has a lot of opportunities to use it. Desert roads in the Valley’s outer edges cross washes at grade, so a dry streambed most of the year becomes a moving river for an hour after a storm upstream, often under blue sky.
The law got its most-cited test in 2005, when a Cave Creek man drove his Hummer around barriers into a flooded road. The rescue cost about $800 and 55 minutes of deputies’ time, and he was charged in Cave Creek Municipal Court. Few cases followed.
What it is not
It is not a traffic ticket. The statute creates liability for costs, not an offense with a fine, so drivers who are cited usually face a separate charge such as reckless driving. It does not apply when there were no barricades: drivers caught by a flash flood on an open road are not covered. And it is not automatic. Each agency decides whether to bill.
The fine print
The statute has three conditions, and all must be met: water covering a public street or highway, barricades placed because of flooding and driven around, and an emergency response. Covered expenses are the reasonable costs of police, firefighting, rescue and emergency medical services at the scene, including the salaries of the people who respond, up to $2,000 for a single incident.
Enforcement is thin by design. In 2018 the Maricopa County Sheriff’s Office told Cronkite News it does not charge people under the law, describing rescues as something residents already pay for; deputies respond to 12 to 24 water rescues a year. Rescuers worry about the opposite problem: people who delay calling 911 because they think they will be billed. A review in the Tucson area found a single citation by Tucson police, in January 2016, across five years, while fire departments there answered more than 250 stranding and swift-water calls between 2015 and 2018, including 54 on one day during Tropical Storm Javier in August 2016.
The physics is why it exists. The National Weather Service says six inches of moving water can knock a person down, a foot will float many vehicles, and two feet of rushing water can carry away most SUVs and pickups. In Scottsdale the city built the Indian Bend Wash Greenbelt to flood on purpose, with roads bridged over it. The risk now is at the edges: the dip crossings of the Rio Verde Foothills and the roads toward Cave Creek.