Can Alcohol Increase Driving Errors Without a Significant Rise in Simulator Crashes?

Yes. A small simulator study found more driving errors after alcohol without a statistically significant increase in its combined critical-situation-and-collision outcome. The null collision finding does not negate the error findings, and the positive error findings do not provide a real-world crash probability for an individual driver.

Kenntner-Mabiala and colleagues’ 2015 alcohol-calibration study illustrates why DUI evidence should identify the actual endpoint rather than compress every driving result into “impaired” or “unimpaired.”

A crossover test with several driving scenarios

Twenty-four healthy licensed drivers completed placebo and two alcohol conditions in randomized, double-blind, counterbalanced order. They were selected from a driver panel with substantial simulator familiarization and good simulator tolerance.

The approximately hour-long course included rural roads, highway and urban sections, with easy, winding and monotonous tracking scenarios. Trained blinded investigators recorded errors, while software measured position, speed and other outcomes.

Scenarios requiring responses to sudden unexpected events were deliberately avoided because repeated exposure can produce practice effects. That choice is particularly relevant when interpreting the collision endpoint: the course was not designed as a repeated emergency-hazard test.

Actual alcohol exposure changed during the drive

The nominal conditions were 0.05% and 0.08%, but the paper reports breathalyzer-derived mean values of 0.058% at the start and 0.044% at the end of the lower condition, and 0.079% and 0.077% in the higher condition. The instrument was a Dräger 7410.

These were breath-based exposure measurements expressed in BAC terminology, not paired venous whole-blood ethanol assays. The nominal condition should not be assigned as an exact measured concentration throughout each participant’s drive. Serum/plasma, urine and biomarkers were not substitute exposure measures here.

Total errors distinguished the three conditions

Mean total recorded errors increased from 50.2 with placebo to 71.6 in the lower alcohol condition and 86.2 in the higher condition. All three pairwise comparisons were significant. Total errors were the only reported endpoint that significantly distinguished every condition from the others.

Separate lateral-control, longitudinal-control and cognitive-error categories differed between alcohol and placebo, but did not all distinguish the two alcohol conditions. The combined critical-situations-and-collisions outcome did not significantly increase (reported p = .958).

That very nonsignificant result is not a demonstrated reduction in risk, proof of equivalence or evidence that alcohol cannot cause crashes. Small-sample studies and selected scenarios may detect common performance errors more readily than uncommon critical events.

Lane keeping depended on the road scenario

Lane-position variability distinguished alcohol from placebo in simple and monotonous sections, but not on the winding road. Conversely, lane departures increased on the winding road, while none occurred in the easiest section.

The choice of metric therefore mattered as much as the general label “lane keeping.” A null lane-variability result in one scenario did not mean every lateral-control measure was unchanged.

Some tactical outcomes also remained nonsignificant, including accepted gap size and percentage of highway time spent in the left lane. These null findings should remain visible rather than be replaced by a claim that every driving behavior deteriorated.

Observer ratings were not identical to error counts

Overall blinded observer ratings differed significantly between placebo and the higher alcohol condition. The lower-versus-placebo comparison was only trend-level (p = .061), and observer ratings did not significantly distinguish the two alcohol conditions.

Participants rated their own driving as worse with alcohol, again without significantly separating the two doses. A global impression and a detailed count therefore provided related but different information.

Limits on DUI and drug-comparison conclusions

The study involved trained simulator users, one apparatus and a selected course. It lacked psychoactive-drug screening and did not tightly restrict caffeine or nicotine. Real traffic, unfamiliar drivers, other doses and emergency situations may produce different results.

Alcohol calibration can benchmark a particular drug-related outcome under comparable experimental conditions. It cannot establish that two substances have identical effects across every task or that a defendant with a similar error count had a particular BAC.

This extends the site’s lane-weaving experiment by examining an error profile and several scenarios. The appropriate case opinion still requires actual measurements, timing and observed behavior; neither the null collision outcome nor the positive total-error outcome independently resolves crash causation or a legal violation.

Primary source

Kenntner-Mabiala R, Kaussner Y, Jagiellowicz-Kaufmann M, Hoffmann S, Krüger HP. Driving Performance Under Alcohol in Simulated Representative Driving Tasks: An Alcohol Calibration Study for Impairments Related to Medicinal Drugs. Journal of Clinical Psychopharmacology. 2015;35:134–142. https://doi.org/10.1097/JCP.0000000000000285.