DUI of Marijuana is Difficult to Prove
Recreational marijuana use became legal in California on January 1, 2018. Two years later, January 1, 2020, recreational pot became legal in Illinois. You can have cannabis in your car legally, but smoking it while driving is illegal. Even more significant is that a driver who ingested marijuana and is driving in an impaired fashion may be ticketed for driving under the influence (DUI) of marijuana.
However, district attorneys and prosecutors face a very difficult tasking in presenting sufficient evidence to justify a conviction of DUI of cannabis. Proving pot-impaired driving is not like proving alcohol impaired driving. Almost 100 years of social science and scientific research support a direct connection between consuming alcohol and driving impaired. Moreover, the scientific community almost unanimously agrees that a person is under the influence of alcohol for driving if their blood alcohol content is .08 percent or more. Such support does not exist in regards to cannabis or marijuana.
In 2016 National Highway Traffic and Safety Administration published a report that said that "a quantitative threshold for per se laws for THC following cannabis use cannot be scientifically supported." Simply speaking, there is no threshold to show that a person is too high to drive similar to the .08 percent blood alcohol content for alcohol use. Similarly, the field sobriety tests were designed and proven to be effective for drivers suspected to be under the influence of alcohol. There has been no studies scientifically verifying their helpfulness for drivers under the influence of marijuana.
Moreover, there is no authorized chemical tests for THC such as a breathalyzer. Even more difficult is that experts have not agreed on how much marijuana is too much for driving. Some states such as Illinois and Washington have set the limit at 5 nanograms. However, experts challenge this because he person who ingested pot over a week ago and is clearly not high can have such small amounts of THC in their blood.
Prosecutors and police officers do not have field sobriety tests and they don't have any kind of chemical test devices to prove DUI of marijuana — so how do they prove it? Police officers rely on their observations of erratic driving, bloodshot eyes, smell of marijuana, instability of the driver when alighting from the vehicle and other sorts of circumstantial evidence.
An effective criminal defense attorney should jump at this opportunity to challenge such indirect evidence. Bloodshot, watery eyes can be caused by tiredness, allergies, or other external conditions. Mechanical problems may cause driving errors. Pulling over a car on a dirt shoulder may instigate the driver to stumble when exiting his car. This where an experienced criminal lawyer needs to narrate a competing story based on circumstantial evidence.