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BACKGROUND: Despite increasing medical cannabis use, research has yet to establish whether and to what extent products containing delta-9-tetrahydrocannabinol (THC) impact driving performance among patients. Stable doses of prescribed cannabinoid products during long-term treatment may alleviate clinical symptoms affecting cognitive and psychomotor performance. AIM: To examine the effects of open-label prescribed medical cannabis use on simulated driving performance among patients. METHODS: In a semi-naturalistic laboratory study, 40 adults (55% male) aged between 23 and 80 years, consumed their own prescribed medical cannabis product. Driving performance outcomes including standard deviation of lateral position (SDLP), the standard deviation of speed (SDS), mean speed and steering variability were evaluated using the Forum8 driving simulator at baseline (pre-dosing), 2.5 h and 5 -h (post-dosing). Perceived driving effort (PDE) was self-reported after each drive. Oral fluid and whole blood samples were collected at multiple timepoints and analysed for THC via liquid chromatography-mass spectrometry. RESULTS: A significant main effect of time was observed for mean speed (p = 0.014) and PDE (p = 0.020), with patients displaying modest stabilisation of vehicle control, increased adherence to speed limits and reductions in PDE post-dosing, relative to baseline. SDLP (p = 0.015) and PDE (p = 0.043) were elevated for those who consumed oil relative to flower-based products. Detectable THC concentrations were observed in oral fluid at 6-h post-dosing (range = 0-24 ng/mL). CONCLUSIONS: This semi-naturalistic study suggests that the consumption of medical cannabis containing THC (1.13-39.18 mg/dose) has a negligible impact on driving performance when used as prescribed.

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Despite sleepiness being considered one of the main factors contributing to road crashes, and even though extensive efforts have been made in the identification of techniques able to detect it, the assessment of fitness-to-drive regarding driving fatigue and sleepiness is still an open issue. In the literature on driver sleepiness, both vehicle-based measures and behavioral measures are used. Concerning the former, the one considered more reliable is the Standard Deviation of Lateral Position (SDLP) while the PERcent of eye CLOSure over a defined period of time (PERCLOS) seems to be the most informative behavioral measure. In the present study, using a within-subject design, we assessed the effect of a single night of partial sleep deprivation (PSD, less than 5 h sleeping time) compared to a control condition (full night of sleep, 8 h sleeping time) on SDLP and PERCLOS, in young adults driving in a dynamic car simulator. Results show that time-on-task and PSD affect both subjective and objective sleepiness measures. Moreover, our data confirm that both objective and subjective sleepiness increase through a monotonous driving scenario. Considering that SDLP and PERCLOS were often used separately in studies on driver sleepiness and fatigue detection, the present results have potential implications for fitness-to-drive assessment in that they provide useful information allowing to combine the advantages of the two measures for drowsiness detection while driving.

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Background: Δ9-Tetrahydrocannabinol (THC) is the psychoactive component in cannabis and a relationship of THC to driving impairment is expected. Despite this, there are discrepant findings with respect to the relationship of blood THC to driving. This study investigated the relationship of blood, urine, and saliva THC/THC-COOH levels to "weaving," as measured by a driving simulator. Methods: Participants smoked cannabis alone or with alcohol. THC/THC-COOH levels in blood, urine, and saliva were correlated with standard deviation of lateral position (SDLP), measuring "weaving." In addition, SDLP after cannabis and/or alcohol were compared with SDLP after placebo when THC/THC-COOH levels were above or below specified thresholds in blood (5 ng/mL), urine (50 ng/mL), or saliva (25 ng/mL). Results: A clear linear relationship between blood THC concentration and SDLP was not observed based on calculation of Spearman coefficients. When compared with placebo, SDLP was significantly increased after cannabis and cannabis combined with alcohol when THC in the blood was above the legal limit. SDLP was increased in drug conditions when saliva cutoffs were above the legal limit. Conclusions: The findings of this study suggest that specified thresholds for THC in blood and saliva may be able to detect driving impairment, but future studies are needed. ClinicalTrials.gov ID: NCT03106363.

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RATIONALE: The effects of hypnotics on automobile driving have been attracting increasing attention. However, few driving simulators (DSs) have been confirmed to have acceptable reliability and validity for assessing the next-day residual effects of zopiclone as a positive control on driving performance. OBJECTIVE: To investigate whether a new DS could permit detection of the next-day residual effects of zopiclone on driving performance. METHODS: In this double-blind, randomized, placebo-controlled crossover trial, 28 healthy males received zopiclone 7.5 mg at bedtime on days 1 and 8 and placebo on the other days over a period of 16 days. The participants took part in three driving tasks-road-tracking, car-following, and harsh-braking-using a DS on days 2 and 9 at 9-h post-dosing. Scores on the Karolinska Sleepiness Scale and Profile of Mood States-Second Edition were then assessed, as was the serum concentration of zopiclone. RESULTS: The estimated differences in the standard deviation of lateral position (cm) in the road-tracking task between the zopiclone and placebo groups on days 2 and 9 were 3.75 cm (90% confidence interval (CI): 1.71-5.79) and 4.07 cm (90% CI: 2.02-6.11), respectively. The estimated differences in the distance coefficient of variation in the car-following task and in the brake reaction time in the harsh-braking task between the zopiclone and placebo groups on day 2 were 4.31 (90% CI: 1.94-6.69) and 24.6 ms (90% CI: 12.7-36.4), respectively. CONCLUSIONS: The DS used in this study has sufficient sensitivity to detect the next-day residual effects of zopiclone on driving performance.

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BACKGROUND: Intranasal esketamine demonstrates rapid improvement of depressive symptoms. However, transient adverse effects (dissociation, sedation and dizziness) may occur, which could impact driving performance. AIMS: To evaluate the effects of 84 mg intranasal esketamine on driving performance in unipolar major depressive disorder (MDD) or persistent depressive disorder (PDD) patients. METHODS: The study consisted of two parts. Part A was a single-blind, double-dummy, randomized three-period, cross-over study to compare effects of esketamine versus placebo on next morning driving, 18 ± 2 h post-treatment. Alcohol was administered to demonstrate assay sensitivity. In Part B, same-day driving, 6 ± 0.5 hours post-treatment, was assessed during twice weekly esketamine administration for 3 weeks. Twenty-seven patients with mild-to-moderate MDD or PDD without psychotic features completed a 100 km on-the-road driving test on a public highway in normal traffic. The primary outcome was standard deviation of lateral position (SDLP; cm; weaving of car). RESULTS: In Part A, alcohol impaired driving performance compared to placebo: Least-square means (95% CI), p-value for delta SDLP (cm) compared with placebo: (ΔSDLP = + 1.83 (1.03; 2.62), p < 0.001), whereas esketamine did not: (ΔSDLP = -0.23 (-1.04; 0.58), p = 0.572). In Part B, weekly driving tests showed no differences between placebo baseline SDLP and after esketamine administration over 3 weeks: Day 11: (ΔSDLP = -0.96 (-3.72; 1.81), p = 0.493), Day 18: (ΔSDLP = -0.56 (-3.33; 2.20), p = 0.686) and Day 25: (ΔSDLP = -1.05 (-3.82; 1.71), p = 0.451). CONCLUSIONS: In this study, esketamine did not impair on-road driving performance the next morning following a single dose, or on same day after repeated administration.

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Driver's drowsiness is one of the high-risk road behaviors that quadruples the risk of road accidents. Measures to deal with drowsiness during driving include listening to music. The present study investigates the effect of two types of music, namely Iranian high-tempo pop and classical music, on mental and physiological drowsiness during driving. Twelve male students at Tehran University of Medical Sciences within the normal range of the Epworth Drowsiness Scale (ESS) participated in this study. Two types of music (classical and pop) were assessed on two separate days with an interval of one week. The mental aspect of drowsiness was evaluated using the Karolinska Sleepiness Scale (KSS), the physiological aspect by monitoring the EEG and heart rate, and the functional aspect through the mean and standard deviation of speed and the Standard Deviation of Lateral Position (SDLP) in a driving simulator. The results showed that the brain waves (four algorithms (1) (θ + α)/ß, (2) α/ß, (3) (θ + α)/(α + ß) and (4) θ/ß), the KSS score, SDLP and standard deviation of speed all decrease while the mean heart rate increases when listening to music during driving compared to driving without music. No significant difference was observed in the mean speed when exposed to music. Moreover, no difference was observed between the effect of the two music styles, i.e. Iranian classical and pop music. Listening to Iranian classical and pop music while driving improves the driver's performance and reduces drowsiness. The present study showed that higher tempo music during driving can reduce drowsiness and change physiological responses and driving performance.

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OBJECTIVE: Results of observational investigations have demonstrated that the risk of a traffic accident is independent of use of AEDs. However, no reports of driving tests conducted with patients administered AEDs have been presented. This study examined this scenario in a simulated driving setting. METHODS: Driving performance of 43 patients with epilepsy (PWE) and prescribed an AED, who were licensed to drive and drove regularly (subject group), was assessed, with the results compared to 40 age- and gender-matched healthy volunteers (control group). Daily driving skills associated with a traffic accident were examined using two different tests provided by a driving simulator software package, road-tracking and car-following. Standard deviation of lateral position (SDLP) and distance coefficient of variation (DCV) were determined as primary and exploratory outcomes, respectively. RESULTS: There was no statistically significant difference for primary outcome shown by SDLP between the subject and control groups (p = 0.906), nor for exploratory outcome shown by DCV (p = 0.063). Multiple regression analysis revealed that age (ß=0.967, p = 0.001), female gender (ß=0.469, p<0.001), and duration of driving experience (ß=-0.583, p = 0.038) were correlated with SDLP. SIGNIFICANCE: The present results demonstrated that the driving performance of PWE taking AEDs was not different from that of healthy volunteers.

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RATIONALE: Although driving simulators (DS) are receiving increasing attention due to concern over traffic accidents under the influences of drugs, few DS are recognized for their reliability and validity. Therefore, the development of an evaluation system using DS for driving performance is urgently needed. OBJECTIVES: To investigate whether the standard deviation of lateral position (SDLP) increases with blood alcohol concentration (BAC) using a DS with reliability and calculate the SDLP threshold from the difference between BAC levels of 0 and 0.05%. METHODS: Twenty healthy Japanese men performed the DS tasks up to 60 min in Study 1 and DS tasks twice at 1-week intervals in Study 2. Twenty-six healthy men conducted the same DS tasks under BAC level (0, 0.025, 0.05, and 0.09%) in double-blind, randomized, crossover trial in Study 3. The primary outcome was SDLP in a road-tracking test. The test-retest reliability of DS data was assessed, and the estimated difference in SDLP between BAC levels of 0 and 0.05% was calculated using a linear regression model. RESULTS: The cumulative SDLP values at 5-min intervals were stable, and the intraclass correlation coefficient for its values was 0.93. SDLP increased with BAC in a concentration-dependent manner. The predicted ΔSDLP value for the difference between BAC levels of 0 and 0.05% was 9.23 cm. No participants dropped out because of simulator sickness. CONCLUSIONS: The new DS used in these studies has reliability, validity, and tolerability and is considered suitable for evaluating the influence of drugs on driving performance.

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BACKGROUND: Standard deviation of lateral position (SDLP) has been accepted as a reliable parameter for measuring driving impairment due to lowered vigilance caused by sleepiness or the use of sedating drugs. Recently, lane drifts were proposed as an additional outcome measure quantifying momentary lapses of attention. The purpose of this study was to validate lane drifts as outcome measure of driver impairment in a large data pool from two independent research centers. METHODS: Data from 11 placebo-controlled studies that assessed the impact of alcohol, hypnotics, and sleep deprivation on actual driving performance were pooled. In total, 717 on-the-road tests performed by 315 drivers were subjected to an automated algorithm to detect occurrences of lane drifts. Lane drifts were defined as deviations > 100 cm from the mean (LDmlp) and from the absolute lateral position (LDalp) for 8 s. RESULTS: The number of LDmlp was low and did not differ between treatments and baseline, i.e., 14 vs. 3 events, respectively. LDalp were frequent and significantly higher during treatment relative to baseline, i.e., 1646 vs. 470 events. The correlation between LDalp and SDLP in the treatment conditions was very high (rs = 0.77). The frequency of the occurrence of treatment-induced lane drifts however depended on baseline SDLP of drivers, whereas treatment-induced changes in SDLP occurred independent of baseline SDLP. CONCLUSION: LDmlp is not useful as an outcome measure of driver impairment due to its rare occurrence, even when treatment-induced increments in SDLP are evident. Treatment effects on LDalp and SDLP are closely related.

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Background: Recent cannabis use is associated with an approximate two-fold increase in automobile crash risk, but detecting cannabis-impaired driving remains a challenge.Objectives and Methods: In this perspective, the pros and cons of two types of assessments arising from those used to detect alcohol-impaired driving are discussed in the context of cannabis-impaired driving.Results: Some laws rely on tests to detect whether blood or breath levels exceed a legally defined (per se) threshold. These laws rely on clear and consistent relationships across individuals between detectable drug concentrations and the amount consumed, crash risk, or degree of driver impairment. However, unlike alcohol, there is poor correspondence between detected levels of the primary active constituent of cannabis or its metabolites and the amount consumed or its behavioral effects. Field sobriety tests assess impairment on functional tests calibrated to reflect actual driving-impairment and validated to predict traffic safety risk. However, functional tests for cannabis-impaired driving have not been developed or validated, and the degree of impairment resulting from recent cannabis use is difficult to distinguish from other conditions such as advancing age or use of certain medications.Conclusions: Although standard field sobriety tests have advantages over per se tests for cannabis-impaired driving, limitations of both leave cannabis users and law enforcement officials little guidance in assessing an individual's driving fitness after recent cannabis use. General strategies for detecting and preventing impaired driving regardless of the cause would be preferable to establishing specific methods for every situation or substance that could impair driving.

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BACKGROUND: As the disease progresses, patients with Huntington's disease (HD), an inherited neurodegenerative disorder, become less independent in their daily life activities and have to consider if they can still drive a car. For most patients, the decision to quit driving is difficult and affects their independence and social activities. OBJECTIVE: To investigate if cognitive, motor, or psychiatric symptoms can predict driving performance in HD gene carriers using a simulator situation. METHODS: Twenty-nine controls, 28 premanifest HD, and 30 manifest HD participated in this observational, cross-sectional study and underwent neuropsychological, motor, and psychiatric evaluations. All participants drove a motorway scenario in a driving simulator to evaluate driving performance. Group differences were analyzed using Analysis of Covariance and stepwise forward linear regression analysis was used to investigate which clinical assessments were predictors of driving simulator outcomes. RESULTS: Manifest HD drove slower and had less vehicle control in the driving simulator compared to controls and premanifest HD. They also performed worse on all clinical assessments compared to controls. Postural sway and slower speed of information processing were predictors of the driving simulator outcome measures. Psychiatric symptoms were unrelated to simulated driving. There were no significant differences between premanifest HD and controls. CONCLUSIONS: Increased postural sway and slower speed of processing are predictive of driving simulator performance in manifest HD. Worse performance on these clinical tasks might be useful as a first screening and could assist clinicians in their referral for an official on-road driving test.

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OBJECTIVE: In clinical practice, patients with Huntington's disease (HD) often decide to solely drive in their own familiar neighborhoods and not on a motorway or in an unknown area. The aim of the study was to identify differences in driving performance between HD gene carriers and healthy individuals in simulated urban and motorway environments. METHODS: This cross-sectional study included 87 participants (28 premanifest HD, 30 manifest HD, 29 controls). All participants were active drivers and were assessed using a driving simulator, a driving history questionnaire, and the Unified Huntington's Disease Rating Scale. The driving simulator session included urban and motorway scenarios. Analysis of variance and Kruskal-Wallis tests were used to compare urban and motorway driving across all 3 groups. RESULTS: Manifest HD drove slower compared to controls and premanifest HD when speed limits increased (80 and 100 km/h) and they had a less steady speed compared to premanifest HD on the motorway and in a 30 km/h zone. Manifest HD also had a larger standard deviation of the lateral position (i.e., more weaving of the car/less vehicle control) compared to controls and premanifest HD on the motorway. CONCLUSIONS: Manifest HD drive more cautious in a driving simulator when speed limits increase compared to premanifest HD and controls and they have less vehicle control on the motorway. The driving simulator parameters are able to discriminate between manifest HD and healthy individuals, so a driving simulator seems a feasible tool to use when investigating changes in driving in manifest HD.

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Ketamine hydrochloride elicits potent psychotomimetic and neurobehavioural effects which make it incompatible with driving; however, the direct effect on driving performance is yet to be assessed. Using an open label, within-subjects protocol, 15 males and 5 females (mean age = 30.8 years) were administered three fixed, stepwise increasing sub-anaesthetic doses of intravenous (IV) ketamine solution [(i) 8 mg/h IV infusion plus 30 mg bolus, (ii) 12 mg/h IV infusion and (iii) 20 mg/h infusion]. Whole blood ketamine and norketamine concentrations were determined at each treatment step and at 2 h post-infusion. Driving performance was assessed at baseline, at each treatment step and at 2 h post-treatment using a validated computerised driving simulator. Standard Deviation of Lateral Position (SDLP) and Steering Variability (SV) were assessed. Linear Fixed Effect Modelling indicated a main effect for time (dose) for SDLP (F[4,72] = 33.22, p < 0.0001) and SV (F[4,72] = 4.65, p < 0.002). Post-hoc analyses revealed significant differences from baseline at each treatment step for SDLP (all p < 0.001), and for 12 mg/h treatment step for SV (p = 0.049). Post-treatment driving performance returned to baseline levels. Weak positive linear associations were observed between SDLP and whole blood ketamine concentrations (R2 = 0.11, ß = 29.96, p = 0.001) and norketamine (R2 = 0.09, ß = 28.87, p = 0.003). These findings suggest that even under highly controlled conditions, ketamine intoxication significantly alters simulated driving performance. At the highest dose, ketamine produced changes to SDLP considered incompatible with safe driving, highlighting how ketamine consumption may translate to an increased risk of road trauma.

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OBJECTIVE: Screening of drug-induced performance impairment is needed to provide meaningful information for users and prescribers regarding the impact of drugs on driving. The main objective was to assess the effects of oxazepam 10 mg (OXA10), oxazepam 30 mg (OXA30), and diazepam 10 mg (DIA10) on standard deviation of lateral position (SDLP) in a highway driving test in actual traffic and to determine the ability of eight neurocognitive tests to detect comparable effects. METHODS: Twenty-three healthy volunteers participated in a four-way double-blind, placebo-controlled, crossover study. The highway driving test was conducted between 4 and 5 h after drug intake. A range of neurocognitive tests was conducted before and after driving, 2 and 6 h post-treatment, respectively. RESULTS: Mean SDLP increased by 1.83, 3.03, and 7.57 cm after OXA10, DIA10, and OXA30, respectively. At 2 h post-treatment, all neurocognitive tests, except the useful field of view, showed performance impairment in all active treatments. Effect sizes (ES) were moderate for OXA10, large ES for DIA10, and largest ES for OXA30. Modest correlations were found between changes in SDLP and performance in the attention network test (ANT), the divided attention test (DAT), and the psychomotor vigilance test (PVT). CONCLUSION: OXA10 caused minor, DIA10 moderate, and OXA30 severe driving impairment. No neurocognitive test was both dose dependently sensitive and able to be associated with driving impairment. No neurocognitive test can replace the on-the-road highway driving test.

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RATIONALE: The purpose of this study is to evaluate the single dose effect of intranasal esketamine (84 mg) compared to placebo on on-road driving performance. Mirtazapine (oral, 30 mg) was used as a positive control, as this antidepressant drug is known to negatively affect driving performance. METHODS: Twenty-six healthy volunteers aged 21 to 60 years were enrolled in this study. In the evening, 8 h after treatment administration, participants conducted the standardized 100-km on-road driving test. Primary outcome measure was the standard deviation of lateral position (SDLP), i.e., the weaving of the car. Mean lateral position, mean speed, and standard deviation of speed were secondary outcome measures. For SDLP, non-inferiority analyses were conducted, using +2.4 cm (relative to placebo) as a predefined non-inferiority margin for clinical relevant impairment. RESULTS: Twenty-four participants completed the study. No significant SDLP difference was found between esketamine and placebo (p = 0.7638), whereas the SDLP after mirtazapine was significantly higher when compared to placebo (p = 0.0001). The upper limit of the two-sided 95% confidence interval (CI) of the mean difference between esketamine and placebo was +0.86 cm, i.e., <+2.4 cm, thus demonstrating that esketamine was non-inferior to placebo. Non-inferiority could not be concluded for mirtazapine (+3.15 cm SDLP relative to placebo). No significant differences in mean speed, standard deviation of speed, and mean lateral position were observed between the active treatments and placebo. CONCLUSIONS: No significant difference in driving performance was observed 8 h after administering intranasal esketamine (84 mg) or placebo. In contrast, oral mirtazapine (30 mg) significantly impaired on road driving performance.

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RATIONALE: Chronic non-cancer pain (CNCP) is a major health problem. Patients are increasingly treated with chronic opioid therapy (COT). Several laboratory studies have demonstrated that long-term use of opioids does not generally impair driving related skills. But there is still a lack of studies investigating on-the-road driving performance in actual traffic. OBJECTIVES: The present study assessed the impact of COT on road-tracking and car-following performance in CNCP patients. METHODS: Twenty CNCP patients, long-term treated with stable doses of opioid analgesics, and 19 healthy controls conducted standardized on-the-road driving tests in normal traffic. Performance of controls with a blood alcohol concentration (BAC) of 0.5 g/L was used as a reference to define clinically relevant changes in driving performance. RESULTS: Standard Deviation of Lateral Position (SDLP), a measure of road-tracking control, was 2.57 cm greater in CNCP patients than in sober controls. This difference failed to reach statistical significance in a superiority test. Equivalence testing indicated that the 95% CI around the mean SDLP change was equivalent to the SDLP change seen in controls with a BAC of 0.5 g/L and did not include zero. When corrected for age differences between groups the 95% CI widened to include both the alcohol reference criterion and zero. No difference was found in car-following performance. CONCLUSIONS: Driving performance of CNCP patients did not significantly differ from that of controls due to large inter-individual variations. Hence in clinical practice determination of fitness to drive of CNCP patients who receive opioid treatments should be based on an individual assessment.

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The present study mainly aimed to assess whether and how sleepiness due to sleep deprivation interacts with Time on Task (ToT) effects both on electroencephalography (EEG) measures and driving performance in real driving conditions. Healthy participants performed a one hour on-the-road monotonous highway driving task while EEG was recorded continuously after one night of normal sleep and after one night of total sleep deprivation. The main outcome parameter in the highway driving test was the Standard Deviation of Lateral Position (SDLP). SDLP and EEG indices (i.e alpha and theta power spectra) increased after sleep deprivation and varied with ToT. The latter was more pronounced after sleep deprivation. Beta power spectra did not differ between conditions but increased with ToT. Changes in SDLP and EEG did not correlate significantly. We conclude that driving performance as well as fatigue and sleepiness fluctuations with ToT were more evident after sleep deprivation as compared to normal sleep.

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Insomniacs report decreased performance in daily routines, which may have detrimental consequences for car driving. We compared changes over time in driving performance (measured as Standard Deviation of Lateral Position - SDLP) and background EEG between 20 untreated insomnia patients (52-70 years old) and 21 normal sleepers (54-73 years old) during a 1h on-the-road driving test after a normal night of sleep, in the morning. SDLP did not differ between groups and increased slightly over time to similar degrees in both groups. EEG alpha and beta power were lower in insomniacs as compared to normal sleepers. Alpha and beta power slightly reduced during driving in normal sleepers but remained at a constant low level in insomniacs. Changes in EEG power and SDLP were not related. It is concluded that on-the-road driving performance does not differ between older insomniacs and older normal sleepers and that changes in spectral EEG measures of cortical arousal and in driving performance are not related.

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The development of effective and safe antidepressant medications is ongoing, and driving studies are critical to assess a drug's safety. The current review summarizes the effects of a sedating effective antidepressant, mirtazapine, on driving ability, and its potential to serve as positive control drug in future driving studies. Three on-road driving studies and four driving simulator studies of mirtazapine were identified. The studies, conducted in healthy volunteers, showed a significant dose-dependent driving impairment, the first day following bedtime administration of mirtazapine. The magnitude of impairment after a single dose of 15 mg or 30 mg mirtazapine was comparable to that observed with a blood alcohol concentration of 0.05%, the legal limit for driving in many countries. After 1 or 2 weeks of daily treatment with mirtazapine, partial tolerance developed to mirtazapine's effects on driving. Driving studies conducted in patients were less informative, as the effect on driving caused by mirtazapine was obscured by a drug-disease interaction and increased variability in patient groups. In conclusion, mirtazapine is useful as positive control drug to assess the potential effects of new antidepressant drugs on driving. Studies in normal healthy volunteers are more sensitive to drug effects than studies in patient populations.

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BACKGROUND: The traditional outcome measure of the Dutch on-the-road driving test is the standard deviation of lateral position (SDLP), the weaving of the car. This paper explores whether excursions out-of-lane are a suitable additional outcome measure to index driving impairment. METHODS: A literature search was conducted to search for driving tests that used both SDLP and excursions out-of-lane as outcome measures. The analyses were limited to studies examining hypnotic drugs because several of these drugs have been shown to produce next-morning sedation. RESULTS: Standard deviation of lateral position was more sensitive in demonstrating driving impairment. In fact, solely relying on excursions out-of-lane as outcome measure incorrectly classifies approximately half of impaired drives as unimpaired. The frequency of excursions out-of-lane is determined by the mean lateral position within the right traffic lane. Defining driving impairment as having a ΔSDLP > 2.4 cm, half of the impaired driving tests (51.2%, 43/84) failed to produce excursions out-of-lane. Alternatively, 20.9% of driving tests with ΔSDLP < 2.4 cm (27/129) had at least one excursion out-of-lane. CONCLUSIONS: Excursions out-of-lane are neither a suitable measure to demonstrate driving impairment nor is this measure sufficiently sensitive to differentiate adequately between differences in magnitude of driving impairment.

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