Current methamphetamine users showed more speeding by distance, greater lane-position variability and shorter turning gaps than comparison drivers in a small simulator study. The experiment did not establish that an individual’s blood methamphetamine concentration predicts driving impairment, or that methamphetamine alone caused the group differences.
Bosanquet and colleagues’ Driving on ice is a human primary investigation of people with ongoing use histories. It is neither an animal experiment nor a randomized drug-administration trial. That distinction determines how its findings can be used.
The final sample comprised 15 current users and 15 controls, matched on age, gender and driving experience. Users reported at least weekly methamphetamine use during the preceding three months. Researchers did not standardize their dose, route or time of consumption. Most met criteria for methamphetamine dependence.
Participants drove a 9.5-kilometer course in a fixed-base simulator after practice. The course included traffic, speed limits, overtaking decisions and a turn across oncoming traffic. Instructions introduced time pressure while requiring compliance with road rules. These conditions probe selected decisions and vehicle-control measures; they do not reproduce every feature of real driving.
The user group spent 16.95% of the route above the speed limit, compared with 9.53% among controls (p = 0.012). Lateral-position variability was greater (p = 0.024). Users also accepted shorter gaps in the right-turn task (p = 0.039). Because this was an Australian scenario, the turn crossed oncoming traffic; the direction should not be detached from that road setting.
Average speed was numerically higher among users, but its comparison did not meet the study’s 0.05 significance criterion (p = 0.052). Centerline crossings, separate speed-exceedance counts and collisions also did not differ significantly. More distance spent speeding and more discrete speeding events are different endpoints. The significant first finding cannot substitute for a significant result on the second.
Blood was collected after driving. One user could not supply a specimen, leaving 14 user specimens for toxicological assessment. Eleven were positive for methamphetamine and ten for amphetamine. Those are separate analytes; the counts should not be described as 15 independently confirmed methamphetamine-positive blood results.
The paper describes a clot-activator collection tube and calls the quantitative findings blood levels. It does not fully resolve the processed specimen fraction in its published methods, so these results should retain that qualification rather than being confidently relabeled serum or validated whole-blood values. Initial screening and subsequent GC/MS quantification also perform different analytical functions.
Within the users with available blood, methamphetamine concentration was not significantly correlated with lane variability, mean speed or distance spent speeding. Reported correlations were 0.154, 0.034 and −0.079, respectively, all p > 0.05. These null findings do not establish the universal absence of drug effects. They show that the three outcomes were not significantly predicted by concentration in this small dataset.
Users differed from controls in impulsivity and other characteristics. Some had additional drugs detected, and histories of alcohol and cannabis use complicated the comparison. Subjective sleepiness and brief cognitive-screen scores did not differ significantly, but those assessments cannot exclude every relevant difference in fatigue or executive function.
Accordingly, this study supports a group association with selected risky simulator behaviors. It cannot separate acute drug effects from chronic exposure, withdrawal, other substances or preexisting characteristics. Applying it to a particular collision requires the actual driving record, specimen timing, analytical documentation and competing explanations.
Compare this naturalistic design with our account of a placebo-controlled d-methamphetamine experiment. The studies ask different questions; neither supplies a universal individual impairment cutoff.
Bosanquet D, et al. Driving on ice: impaired driving skills in current methamphetamine users. Psychopharmacology. 2013;225:161–172. doi:10.1007/s00213-012-2805-y.