IntroductionThe on-the-road highway driving test is generally regarded as a gold standard for assessing drug-induced driving impairment. The primary outcome measure is the standard deviation of lateral position (SDLP), a measure of road tracking error or “weaving”. The test has been calibrated for incremental doses of alcohol almost 30 years ago in order to define the impact of drug-induced impairment in terms of blood alcohol concentration (BAC) equivalents. Drug-induced changes in SDLP exceeding 2.4 cm have been evaluated as clinically relevant ever since. The present analysis was conducted to assess the robustness of the alcohol effect in a range of on-the-road driving studies which have been conducted since the initial alcohol calibration study.MethodsThe present study pooled data of 182 participants from nine placebo-controlled crossover studies who performed the highway driving test, while their BAC was at or just below the legal limit for drivers (i.e., 0.5 g/L).ResultsOverall, mean SDLP increased with 2.5 cm (95% CI 2.0–2.9 cm). Equivalence testing showed that the clinical relevance criterion value of 2.4 cm fell well within the 95% CI in each individual study. Gender did not affect alcohol-induced changes in SDLP.DiscussionThese results demonstrate the robustness and validity of the clinical relevance criterion for SDLP as measured during on-the-road driving.

Depression is a mental disorder likely to affect everyday functions. The present study aimed to assess actual driving performance of depressed patients who were without specific antidepressant treatment or received long-term antidepressant treatment. A standardized on-the-road driving test was used to assess standard deviation of lateral position (SDLP) in 3 patient groups receiving either no antidepressant treatment (with or without benzodiazepine medication) or treatment with selective serotonin/noradrenalin reuptake inhibitors for a period of 6-52 weeks. Severity of depression was assessed using Beck's Depression Inventory and the Hamilton Depression Rating Scale. The performance of patient groups was compared to healthy controls. The mean SDLP of untreated and treated patients was significantly higher than that of healthy controls. Driving impairment in the long-term treated group was significantly less than in the untreated groups. SDLP was positively correlated to severity of depression across all groups. It is concluded that symptoms of depression are a major cause of driving impairment. Reductions in severity of depression through antidepressant treatment reduce severity of driving impairment.

Objective The aim of this study is to compare actual driving performance and skills related to driving of patients using benzodiazepine anxiolytics or hypnotics for at least 6 months to that of healthy controls. Methods Participants were 44 long‐term users of benzodiazepine and benzodiazepine‐related anxiolytics (n = 12) and hypnotics (n = 32) and 65 matched healthy controls. Performance was assessed using an on‐the‐road driving test measuring standard deviation of lateral position (SDLP, in cm) and a battery of neurocognitive tasks. Performance differences between groups were compared with a blood alcohol concentration of 0.5 mg/ml to determine clinical relevance. Results Compared with controls, SDLP was significantly increased in hypnotic users (+1.70 cm) but not in anxiolytic users (+1.48 cm). Anxiolytic and hypnotic users showed significant and clinically relevant impairment on neurocognitive task measuring executive functioning, vigilance, and reaction time. For patients using hypnotics for at least 3 years, no significant driving impairment was observed. Conclusion Impairing effects of benzodiazepine hypnotics on driving performance may mitigate over time following longer term use (i.e. 3 years or more) although neurocognitive impairments may remain.

Acute benzodiazepine intoxication produces severe impairment of neurocognitive skills related to driving. It is less clear whether such impairments also occur in patients who use benzodiazepines chronically. The current review evaluated neurocognitive skills of long-term benzodiazepine users and addressed 2 major questions: do long-term users develop tolerance for the impairing effects of benzodiazepines on neurocognitive performance, and if so, does tolerance warrant a change in driver fitness classification systems that currently deem users of benzodiazepines unfit to drive? Neurocognitive impairments were reported in patients who on average used benzodiazepines for 5–15 years. In addition, sensitivity to acute benzodiazepine impairment decreased in long-term users, suggesting (partial) tolerance. Definitions of clinical relevance of neurocognitive impairments in long-term users and how these were affected by duration of benzodiazepine use were generally lacking. Also, sensitivity of neurocognitive tasks to drug effects and their validity to predict fitness to drive were generally unknown. Because of these limitations, no firm conclusion can be drawn regarding a re-classification of long-term benzodiazepine effects on driver fitness.

Summary Patients with narcolepsy or idiopathic hypersomnia (IH) are at increased risk of driving accidents. Both excessive daytime sleepiness, i.e. unwanted sleep episodes during the day, and disturbed vigilance are core features of these disorders. We tested on‐the‐road driving performance of patients with narcolepsy or IH coming in for a routine driving fitness evaluation and examined: (1) correlations between driving performance and the Maintenance of Wakefulness Test (MWT), Sustained Attention to Response Task (SART) and Psychomotor Vigilance Test (PVT) as objective tests; (2) the predictive power of the MWT and SART for increased risk of impaired driving; (3) the best set of objective predictors for increased risk of impaired driving. Participants were 44 patients (aged 18–75 years) with narcolepsy type 1 (NT1), type 2 (NT2) or IH. They completed the MWT, SART, PVT, a subjective sleepiness questionnaire, and a standardised on‐the‐road driving test. The standard deviation of the lateral position (SDLP) was used as outcome measure of driving performance. The MWT had low correlation with the SDLP (ρ = −0.41 to −0.49, p < 0.01). The SART and PVT had low correlations with SDLP (ρ = 0.30 and ρ = 0.39, respectively, both p < 0.05). The predictive power of MWT for an increased risk of impaired driving was significant, but low (area under the curve = 0.273, p = 0.012), and non‐significant for SART. We conclude that in our present group, none of the tests had adequate ability to predict impaired driving, questioning their use for clinical driving fitness evaluation in narcolepsy and IH. Real‐time monitoring of sleepiness while driving seems more promising in these patients.