Why this page exists
We are a Wisconsin OWI-defense firm. We see clients after the arrest, not before. But the most common thing we hear from a first-time client is some version of “I didn’t think I was that impaired”. The research below is what the National Highway Traffic Safety Administration, the AAA Foundation, and the University of Iowa actually measure. Same science the Wisconsin State Patrol and the District Attorney’s office work from. If you are charged, knowing the science is the first part of building a defense; if you are not, knowing it might keep you out of one.
Alcohol impairment
The popular picture of drunk driving is perceptual — blurry vision, double-vision, slurred speech. The science is mostly cognitive: slower decision-making, worse judgment of speed and distance, overconfidence, and degraded lane-position control. That last one, the steering wobble, is what an officer is trained to look for and what dashcam footage in a 346.63 prosecution shows.
Drive Sober or Get Pulled Over (NHTSA press conference). Source: USDOTNHTSA on YouTube.
Cannabis impairment
AAA Foundation research published in 2025 found that 84.8% of cannabis users will drive on the same day, and 53% will drive within an hour of using. Many do so believing cannabis affects driving less than alcohol. Federally sponsored research at the University of Iowa’s National Advanced Driving Simulator pushes back on that: a driver with a blood-THC concentration of 13.1 µg/L showed lane-weave equivalent to a driver at the 0.08 alcohol legal limit. (Lane-weave is the measurable signal; cognitive and reaction-time effects are harder to film, but worse.)
The World's Most Advanced Driving Simulator. Source: University of Iowa Media Production on YouTube.
Combined alcohol and cannabis
The same NADS study tested six combinations of alcohol and vaporized cannabis at concentrations matched to what is found in arrested drivers. The headline finding: combined use is additive, not synergistic. Drivers using both substances together weave more than drivers using either substance alone, but the combination does not double the impairment of either component. In a Wisconsin prosecution, this matters for two reasons: (1) the State will present both substances together as evidence of impairment under § 346.63, and (2) toxicology timing is contested ground — cannabis metabolites linger long after impairment ends, and a defense investigation often turns on what the blood test actually proves.
National Advanced Driving Simulator highlights. Source: UI Driving Safety Research Institute on YouTube.
What the research can’t show
A driving-simulator clip can show steering wobble. It cannot show what the driver was thinking. The honest case against impaired driving is not the visual blur; it is the worse risk-assessment, the slower decision speed, and the overconfidence that comes with any psychoactive substance. AAA’s 2025 study found that 46.9% of cannabis users believe they drive the same on cannabis as sober. That belief is itself the most dangerous variable. Wisconsin juries hear it from defendants and from witnesses alike, and prosecutors know to cross-examine on it.
Charged with OWI in Wisconsin?
We are Cafferty & Scheidegger, S.C., a Racine criminal-defense firm. Free, confidential consultations, answered 24/7. If you have a refusal-hearing deadline running, call now — the 10-day clock starts at arrest, not at hire.
Authoritative sources cited
- NHTSA — Drive Sober or Get Pulled Over campaign
- NHTSA YouTube channel (USDOTNHTSA)
- AAA Foundation — High Stakes (March 2025)
- AAA Foundation Cannabis Fact Sheet (PDF, Dec 2024)
- University of Iowa NADS — Cannabis & Alcohol study
- Zero in Wisconsin — Impaired Driving (WI DOT)
- Wisconsin OWI penalty chart (official PDF)