The relationship between performance on the standardised field sobriety tests, driving performance and the level of D9-tetrahydrocannabinol (THC) in blood K. Papafotiou*, J.D. Carter, C. Stough Swinburne Centre for Neuropsychology, Swinburne University of Technology, PO Box 218, Hawthorn, Vic. 3122, Australia Received 6 September 2004 received in revised form 23 November 2004 accepted 24 November 2004 Available online 11 January 2005 Abstract The consumption of D9-tetrahydrocannabinol (THC) as cannabis has been shown to result in impaired and culpable driving. Testing drivers for the presence of THC in blood is problematic as THC and its metabolites may remain in the blood for several days following its consumption, even though the drug may no longer have an influence on driving performance. In the present study, the aim was to assess whether performance on the standardised field sobriety tests (SFSTs) provides a sensitive measure of impaired driving behaviour following the consumption of THC. In a repeated measures design, 40 participants consumed cigarettes that contained either 0% THC (placebo), 1.74% THC (low dose) or 2.93% THC (high dose). For each condition, after smoking a cigarette, participants performed the SFSTs on three occasions (5, 55 and 105 min after the smoking procedure had been completed) as well as a simulated driving test on two occasions (30 and 80 min after the smoking procedure had been completed). The results revealed that driving performance was not significantly impaired 30 min after the consumption of THC but was significantly impaired 80 min after the consumption of THC in both the low and high dose conditions. The percentage of participants whose driving performance was correctly classified as either impaired or not impaired based on the SFSTs ranged between 65.8 and 76.3%, across the two THC conditions. The results suggest that performance on the SFSTs provides a moderate predictor of driving impairment following the consumption of THC and as such, the SFSTs may provide an appropriate screening tool for authorities that wish to assess the driving capabilities of individuals suspected of being under the influence of a drug other than alcohol. # 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Marijuana D9-tetrahydrocannabinol SFSTs Driving impairment 1. Introduction Research has indicated that drugs other than alcohol have been detected in as many as 26.7% of drivers killed on Australian roads and that cannabis D9-tetrahydrocannabinol (THC) is the drug that has been most commonly detected [1,2]. Furthermore, research into the culpability of drivers who have been killed in traffic crashes on Australian roads indicates that the odds ratio (relative odds of culpability) of drivers in whom THC was detected was 6.6. The odds ratio is calculated by determining the proportion of drivers respon- sible for crashes to those not responsible for crashes. By way of contrast, the odds ratio of drivers who presented with a blood alcohol concentration (BAC) of between 10 and 15 was 3.7 and the odds ratio of drivers in whom neither drugs nor alcohol were detected was 1.0 [2]. www.elsevier.com/locate/forsciint Forensic Science International 155 (2005) 172���178 * Corresponding author. Tel.: +61 3 9214 5757 fax: +61 3 9214 5230. E-mail address: kpapafotiou@swin.edu.au (K. Papafotiou). 0379-0738/$ ��� see front matter # 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2004.11.009

The consumption of THC has been shown to lead to impaired car control [3], increase the number of obstacles hit on a driving course [4,5], increase the standard deviation of the lateral position of a vehicle [5,6], impair tracking ability [6] and increase the number of sideways movements of a vehicle as well as the percentage of time spent out of a lane [6,7]. Unlike testing for BAC however, the ability to determine whether drivers have consumed THC is limited by a number of factors, not the least of which is the fact that THC and its metabolites may remain in the blood for several days following its consumption, even though the drug may no longer have a deleterious effect on driving performance [1]. Therefore, rather than conducting a test to simply detect the presence of a drug in a driver���s blood, law enforcement officers require a tool that will allow them to determine whether an individual���s driving behaviour is impaired fol- lowing the consumption of a drug. The standardised field sobriety tests (SFSTs) are currently being used in Victoria, Australia for this purpose [8], despite the fact that no studies have been conducted in order to determine whether perfor- mance on the SFSTs provides an accurate indicator of driving behaviour following the consumption of a drug other than alcohol. The SFSTs have been demonstrated to be sensitive tests of impairment related to a BAC of up to 0.08% [9,10] and it has been argued that the SFSTs provide an accurate indicator of driving impairment caused by the consumption of alcohol [9,11���13]. The consumption of THC has also been found to impair performance on the SFSTs [14]. Furthermore, the drug evaluation and classification program (DECP) (a 12 step testing program that includes the administration of the SFSTs) has previously been found to reliably indicate whether individuals have consumed drugs other than alcohol [15,16]. However, these studies have only revealed that the SFSTs provide an indicator of whether a drug has been consumed, they have not indicated whether performance on the SFSTs provides a predictor of impaired driving beha- viour following the consumption of a drug other than alcohol. Therefore, the aim of the present study was to assess whether performance on the SFSTs provides an indicator of impaired driving behaviour following the con- sumption of THC. A further aim of the present study was to determine whether the inclusion of a new sign in the SFST scoring procedure may improve the sensitivity of the SFSTS as a measure of driving impairment. The additional sign, head movements or jerks (HMJ) during performance of the horizontal gaze nystagmus (HGN) test, is not traditionally included in the SFST scoring procedure but is considered to be a possible symptom of drug use [8]. Inclusion of HMJ has previously been shown to increase the number of subjects classified as impaired on the SFSTs following the consump- tion of THC [14]. As the consumption of THC has been shown to impair driving performance and has also been shown to impair performance on the SFSTs, it was hypothesised that scores obtained from the administration of the SFSTs would cor- rectly predict whether the driving behaviour of participants was impaired. It was further hypothesised that scores obtained from the administration of the SFSTs would pro- vide a better predictor of driving impairment when the sign HMJ was included in the scoring procedure. 2. Materials and methods 2.1. Participants Forty healthy participants (14 female and 26 male), aged between 21 and 35 years (M = 25.5, S.D. = 3.1) who had previously smoked cannabis participated in the study. Parti- cipants were recruited through advertisements. Prior to the commencement of testing, participants were required to undergo a medical examination that was performed by a general medical practitioner. Participants were required to complete a drug-use questionnaire and were requested to refrain from the use of all drugs other than alcohol, including medications, in the 7 days preceding the experimental session. Exclusion criteria were: history of cardiac disorders history of substance abuse history of mental health pro- blems history of allergic reactions to drugs and current medical illness. 2.2. Marijuana cigarettes THC was administered to participants using marijuana cigarettes that were provided by the National Institute on Drug Abuse (NIDA) in the USA. Three different THC dosages were used: 0% THC (placebo) a low dose of 1.74% THC (0.813 g) and a high dose of 2.93% THC (1.776 g). 2.3. The standardised field sobriety test All three tests that comprise the SFST battery were administered, as per the administration procedures used by the Victoria Police [8]. These procedures were based on those of Burns and Moskowitz [9] and are outlined below. 2.3.1. Horizontal and vertical gaze nystagmus (HGN and VGN) In this test, participants were required to focus on an object, located 12���15 in. in front of their face, as it moved horizontally and then vertically. The investigator separately observed the left and right eye for the following four signs: lack of smooth pursuit (LSP) distinct nystagmus at max- imum deviation (Nmax) nystagmus onset before 458 (N45) and nystagmus at the vertical position (VGN). If a total of four or more signs were observed, the participant was judged to be impaired to a degree equivalent to a blood alcohol concentration of above 0.10%. An additional sign, head K. Papafotiou et al. / Forensic Science International 155 (2005) 172���178 173