Individuals can have THC detected in their blood or saliva without experiencing any psychotropic effects or exhibiting impairments. Following the use of cannabis, THC and its metabolites can be detected for long periods of time in plasma and urine, ranging from approximately 7 days for occasional users  and up to 30 days for frequent users . The extent to which the behavioural impairments of cannabis use are present depends on a variety of drug- and user-related factors due to the bidirectional and biphasic nature of the drug . These considerations include route of administration, dosage of THC, titration of dose, user tolerance, user intake frequency, environment of administration, and cannabinoid absorption, metabolism, and excretion rates . The current state of enforcement in Canada for roadside testing of cannabis-induced impairment includes the use of Standardized Field Sobriety Tests  and handheld drug screening devices that can detect the presence of cannabis in saliva. While the SFST has been well-validated for impairment due to alcohol, they have been shown to have little sensitivity to impairment from grow lights for cannabis .

If the SFST or handheld saliva device results indicate potential impairment, the administrating officer could demand a qualitative evaluation by a drug recognition evaluator and potentially a blood test at a police station to justify a charge of impaired driving. However, as discussed above, blood THC levels do not directly correlate with levels of behavioural impairment as manifested in driving performance deficits. In essence, measuring THC levels at roadside does not allow comprehensive conclusions to be drawn regarding cannabis-related impairment, thus alternative measures are needed. Much of the previous research examining the link between cannabis use and driving safety consists of epidemiological and observational studies . Reviews of these studies have consistently shown an increased crash risk for drivers who were under the influence of cannabis compared to drivers who had not consumed cannabis , with indications that driving after cannabis consumption is twice as likely as sober driving to result in a collision . However, these studies have several limitations including potentially compromised data validity such as inaccurate blood THC levels reported due to delays between the time of crash and the time of driver blood toxicology analysis and information bias, such as drug presence presumptuously assumed to result in drug impairment .

Another way to determine whether associations and/or causal relationships are observed between grow cannabis use and driving performance is to investigate this link experimentally within controlled settings, including using driving simulators. Simulators are an attractive proxy for the real-world operation of vehicles, as many of the practical, ethical, and safety issues involved with testing human operators under the influence of drugs in the real world are avoided . Sophisticated simulation technology also provides the ability to reproduce conditions in a controlled environment, capture precise measurements of quantitative variables, receive real-time qualitative assessment from trained evaluators, and design targeted test scenarios and conditions, including challenging driving situations. Compared to real world, on-road driving assessments, simulators allow for the safe testing of driving performance without requiring impaired individuals to join live traffic and potentially endanger themselves and others. Simulators ensure that all participants experience the same driving scenario without introducing a wide range of conditions that differ across individuals, such as differences in traffic, road structure, or environmental conditions.

Several previous driving simulation studies have demonstrated associations between cannabis use and changes to driving performance . For instance, it has been shown that poorer lane-keeping, slower reaction times, and slower driving speeds are observed following THC consumption  relative to pre-consumption. These effects on driving performance measures have also been shown to increase in a dose-dependent manner . However, reduced speed and minor within-lane weaving in a generic scenario representing common, everyday driving is not necessarily indicative of performance impairments that compromise driving safety across the wide range of common and challenging situations drivers face in everyday settings. This is likely due to the use of preconfigured scenarios, not customized to this specific research question. To our knowledge, there have been no formally described approaches to provide guidance on how to construct customized driving simulation scenarios that strategically test abilities shown to be affected by cannabis.