296 ment caused by a drug. If these tests, alone or in combination, can predict actual driving performance, they could serve as a time-and cost-effective safe alternative for on-the-road driving tests. Ramaekers (2003) correlated changes in driving perfor- mance (SDLP) and performance in seven psychometric tests (tracking, divided attention, reaction time, vigilance, Critical Flicker Fusion test, tapping, and memory). Analyzing data from two studies (N= 32 in total), he found that correlations were at best relatively modest (r = 0.2 to 0.4). Correlation was highest between SDLP and the tracking test. In the current study, data from a larger sample of healthy volunteers was analyzed, who participated in three studies examining the effects of various CNS drugs on both on-the- road driving and a number of psychometric test. The objective was to determine to what extend performance on the psychometric tests predicts on-the-road driving perfor- mance (SDLP), alone or in combination. Methods Participants Data from three studies was used to compose the current data set (Verster et al. 2002a,b, 2003a,b, 2006). The Medical Ethics Committee of the University Medical Center Utrecht approved the study protocols, and subjects were treated according to ICH guidelines for Good Clinical Practice and the Declaration of Helsinki and its amendments. A total of 96 healthy male and female volunteers completed the three studies. Mean (SD) age was 23.9 (2.2) years old. Written informed consent was obtained before their inclusion. Subjects were medically screened, used no concomitant medication other than acetaminophen and oral contraceptives, and they had no history of alcohol or drug abuse. Before the start and at the end of the studies, blood chemistry and hematology and urinalysis were determined, and a 12-lead ECG was recorded. All assessments were within normal limits. To confirm compliance, at all visits, subjects were tested on the presence of alcohol and drugs of abuse (amphetamines, barbiturates, cannabinoids, benzo- diazepines, cocaine, and opioids). In addition, female subjects underwent β-HCG pregnancy tests. None of the subjects were positive on any of these tests. Subjects possessed a valid driver's license and drove more than 5,000 km/year during each of the past 3 years. A thorough discussion on the inclusion and exclusion criteria of participants and description of the study designs can be found elsewhere (Verster et al. 2002a, b, 2003a, b, 2006). In each study, subjects performed an on-road driving test and a psychometric test battery. The design of the studies was set Psychopharmacology (2012) 220:293–301 up in a balanced manner: half of the subjects first performed the driving test, whereas the other half first performed the psychometric test battery. Treatments A variety of treatments were tested in the three studies, including alcohol, hypnotics, anxiolytics, analgesics, and antihistamine drugs. Study 1 (part 1) examined the residual effects of zaleplon (10 and 20 mg) and zolpidem (10 and 20 mg), 4–6 h after middle of the night administration (Verster et al. 2002a). The results were compared to a single dose of alcohol (a blood alcohol concentration of 0.05%) and alcohol-placebo (study 1, part 2). Study 2 examined the acute effects bromfenac (25 and 50 mg), oxycodone with paracetamol (5/325 and 10/650 mg), and alprazolam (1 mg) (Verster et al. 2002b, 2006). Study 3 examined the acute (day 1) and subchronic (day 4) effects of levocetirizine (5 mg) and diphenhydramine (50 mg) (Verster et al. 2003a, b). In all studies, results were compared with those obtained in a placebo condition. The on-the-road driving test Standardized 100-km driving tests (O’ Hanlon et al. 1982; Verster and Roth 2011a) were performed on a primary highway during normal traffic, between the cities of Utrecht and Arnhem. A camera, mounted on the roof of the test vehicle, measured the vehicle's lateral position relative to the road delineation. Participants were instructed to drive with a steady lateral position within the right traffic lane while maintaining a constant speed of 95 km/h (60 mph). The amount of weaving of the car, measured by the standard deviation of the lateral position (SDLP, centimeter), is the primary outcome parameter. The standard deviation of speed (kilometer per hour) is a secondary parameter. Duration of the driving test was approximately 75 min. Patients were allowed to deviate from the instructions to overtake a slower-moving vehicle in the same traffic lane. The vehicle's speed and lateral position were continuously recorded. A licensed driving instructor who had access to dual controls sat in the right front seat, guarding the subject's safety. Tests could be terminated if the driving instructor or the subject felt it was unsafe to continue. Before disclosure of treatment blinding, the data were edited off-line to remove data that were disturbed by extraneous events (e.g., overtaking maneuvers and traffic jam), and SDLP values were calculated. Psychometric tests All tests were computerized and developed from ERTS (Beringer 1992). Subjects were seated in a soundproof test