Effect of smartphone breathalyzer feedback on willingness to drive in moderately intoxicated individuals: A randomized trial.

OBJECTIVE

The present study examined the impact of smartphone breathalyzer feedback on individuals' decisions to drive when they are moderately intoxicated. Although the legal driving limit for blood alcohol concentration (BAC) in the United States is < 0.08%, crash risk begins to increase at moderate BACs ≥ 0.04%.

METHOD: We conducted a laboratory-based, randomized controlled trial in 20 adult drivers aged 21-39 with a history of binge drinking. Participants were given sex- and weight-based doses of alcohol over 90 min with a target peak BAC of 0.10%. Smartphone breathalyzer measurements were taken every 15 min until the participant's BAC declined to 0.03%. Ten participants received feedback on their BAC readings, while the other 10 were blinded to BAC readings. After each measurement, participants were asked to rate on 10-point scales how much they were intoxicated, able to drive, and willing to drive.

RESULTS

At BACs ≥ 0.04% and < 0.08%, learning about BAC was associated with lower perceived intoxication (-2.0, confidence interval [-3.1, -0.8]), greater perceived ability to drive (2.4, confidence interval [1.0, 3.9]), and greater willingness to drive (3.9, confidence interval [2.5, 5.3]), all ps < .001.

CONCLUSIONS

Being aware of their BAC may make drinkers more willing to drive up to the legal BAC limit of 0.08%, despite being in a range associated with increased crash risk. We recommend that breathalyzer apps provide salient feedback about the risks of driving with a BAC in the moderately intoxicated range. (PsycInfo Database Record (c) 2025 APA, all rights reserved).