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A Reality Check on Perceived BAC and Subjective Intoxication Levels 

Author: Sasha Tanner

What compels someone to drive while impaired?  The key is to understand behavioral processes.  One study analyzes the effects of alcohol to see how risk-taking behaviors differed among several people based on self-perceptions of intoxication levels and how alcohol affected their inhibitory control. 

  • Inhibitory control: the ability to control or manage impulses and respond reasonably 

Study Design 

Before the experiment, the researchers, Heymsfeld and Fillmore (2025), collected information on demographics (such as age and sex), medical history, driving frequency, drinking levels, and drug use across 80 participants based on the following characteristics: 

  • Eligible drivers 
  • 21 to 45 years old 
  • Not currently pregnant 
  • No mental disorders 
  • Not using drugs other than THC (participants had to wait 24 hours for alcohol or THC to leave their system) 

Then, they issued a placebo to the control group and had the experimental group consume a certain level of alcohol before moving on to the simulation. 

Simulating the Driving Experience 

The researchers employed a driving simulator as the primary experimental tool, and the methodology consisted of the following structured procedures: 

  1. Participants self-reported estimates of intoxication based on visual-analog symptoms and guessed their BAC levels on a scale from 0.01% to 0.16% BAC to understand how people perceived their tolerance and capability to drive. 
  1. Then, the simulation displayed a four lane, metropolitan setting without the presence of speed limit signs to gauge the participant’s risk-taking behaviors under the influence of alcohol, which were measured by TTC levels. 
  1. Time-to-collision (TTC): the amount of time that exists between two vehicle bumpers to estimate risk level 
  1. Participants received higher compensation if they completed the simulation in a shorter timeframe, but the longer they took, the less they earned. 
  1. Ex. $5 for <5 minutes, and $0.50 for >10 minutes 
  1. Participants paid $0.50 for each crash 
  1. Following the simulation, the participants were required to undergo a cued go/no-go reaction time (RT) test that lasted 15 minutes, which measured the amount of time it took for the participants to react to a certain stimulus. 
  1. (RT) test used to measure inhibitory control 
  1. For the next 30 days, participants were required to record each day that they chose to drink alcohol to determine whether they were a heavy drinker. 

Results 

Reaction Time Based on Alcohol Consumption 

  • The mean BAC level between men and women was 0.072% BAC 30 minutes after consumption. 
  • TTC levels decreased if the participant consumed alcohol. 
  • Though crash cases were low, they were always associated with alcohol consumption. 
  • For the RT test, those who consumed alcohol had slower reaction time. 

Estimation & Risk-Taking Behaviors 

  • Drivers overestimated their BAC levels 40 minutes after drinking, but the actual levels were 0.0816% BAC. 
  • Among the experimental group that consumed alcohol, 40% overestimated and 33% underestimated their actual BAC levels. 
  • Participants who underestimated their BAC had lower TTC levels. 
  • Drivers with higher risky behaviors—i.e., reduced TTC, crashes, high BAC—tended to underestimate their subjective intoxication levels. 
  • Those who consumed higher amounts of alcohol were subject to risky behaviors due to an impaired inhibitory control system. 
  • There is no relationship between self-reported understanding of intoxication and risky driving. 
  • The people who underestimated their BAC levels drank more throughout the 30 days following the simulation. 
  • Heavy drinkers were more likely to assume they weren’t as intoxicated—but they were more likely to be risky drivers in the simulation. 

Policy Implications 

As mentioned previously, drivers that underestimated their BAC levels had a greater propensity to engage in risky behaviors behind the wheel, yielding a greater need for policy reform around drinking expectations versus reality. 

  1. Research should expand on why underestimated BAC levels were in line with risky driving behavior while underestimated subjective intoxication was not. 
  1. Though compensation can certainly reduce crashing during driving simulations, more alternatives to driving simulations should be explored since the participant believes there are no true consequences, thus altering their behavior. 

In short, alcohol consumption and risky driving go hand-in-hand.  Heavy drinkers may have heightened tolerance, but this does not mean that they are able to drive. Click the link to the source below for more information. 

References