An evaluation of the Standardised Field Sobriety Tests for detection of impairment associated with cannabis with and without alcohol

Reports indicate that in Victoria, New South Wales and Western Australia, 23.5% of drivers in fatal accidents had consumed drugs other than alcohol, and that 29.1% of drivers had a Blood alcohol contentration (BAC) level of 0.05% or higher. Alcohol has been detected in combination with drugs in almost 10% of cases. Cannabis was most prevalent among drugs other than alcohol detected in specimens (13.5%) (Drummer et al., 2003). The combination of drugs as an influence on road traffic accidents is becoming a growing concern and research has been conducted to identify how these drugs impair performance. Krueger & Vollrath (2000) reported that recent consumption of cannabis improved lane positioning; however, when combined with alcohol, lane position deviated, and participants drove faster. The consumption of low dose and high dose cannabis alone has also been associated with an increase in vehicle lane weaving (straddling solid and barrier lines) (Papafotiou, 2004b). Furthermore, a trend towards greater braking latency after consumption of higher doses of cannabis has been reported (Ligouri et al., 1998). Generally, alcohol has been reported to increase hazardous simulated driving, and cannabis has been reported to slow a driver’s speed (Stein et al., 1983). The findings of several studies have directly suggested that the effect of Tetrahydrocannabinol (THC) consumption on driving performance may be greater for nonregular cannabis users than for regular cannabis users (Marks & MacAvoy, 1989; Wright and Terry, 2002; Papafotiou, 2004c). Wright and Terry (2002) also provide evidence to suggest that regular cannabis users may develop cross-tolerance to the effects of drugs and alcohol.