The proliferation of marijuana legalization has changed the relationship between driving and marijuana use. While impaired driving remains illegal, marijuana use that does not result in impairment is not a bar to operating a motor vehicle. Scientists have yet to find a reliable way for law enforcement officers to make this distinction. In the marijuana impairment context, there is not a scientifically proven equivalent to the Blood Alcohol Content standard nor are there reliable roadside assessments. This scientific and technological void has problematic consequences for marijuana users that get behind the wheel and find themselves suspected of impaired driving. Without a marijuana breathalyzer or reliable Field Sobriety Tests, law enforcement officers are forced to find another way to determine impairment. Searching the vehicle for evidence of recent marijuana use can be an attractive option. However, the Fourth Amendment prohibits “search first, find probable cause later” policing. A roadside vehicle search violates a driver’s Fourth Amendment rights if sufficient evidence of impairment is lacking. Until law enforcement can reliably determine marijuana impairment at the roadside, drivers need protection from these unconstitutional searches. This Note addresses how states can disincentivize potential Fourth Amendment violations.
To provide context for this discussion, this Note begins by outlining the history of marijuana’s legal status and summarizing the relevant Fourth Amendment case law. Next, it contrasts the challenges of determining marijuana impairment with the relative ease of testing for alcohol impairment during motor vehicle stops. This Note then presents case studies of three states that each have a distinct legal approach to determining marijuana impairment amongst drivers. Finally, this Note provides prescriptive recommendations for states that have legalized or plan to legalize marijuana. Ultimately, this Note provides the reader with a primer on an important legal issue: how the inability to reliably establish marijuana impairment during a traffic stop creates an incentive for the police to search the vehicle first and find probable cause later.