As long as no one is holding a lit joint.
Drugs affect everyone differently, that's why some people pass out after a small toke and others can power through a days worth of work after consuming enough edibles to kill a small horse. The problem is, now that a few states have legalized medical marijuana with a handful having gone the route of full legalization, the laws regarding impaired driving are trying to play catch up. In five of the six states that have recently legalized marijuana, a driver is convicted for driving under the influence if the THC in their blood surpasses a certain level.
According to a recent study done by the Automobile Association of America, this isn't really a good way to determine if a driver is impaired or not. The study found that some drivers could have TCH levels that exceed the limit but still be perfectly capable of driving a car. Meanwhile some drivers that fall under the limit can have a different reaction to the marijuana and be too high to drive. Another thing to consider is how experienced a user is. Medical patients and heavy users tend to have lower THC counts in their bloodstreams than infrequent consumers, although their blood tends to retain THC for longer periods of time. Frequent users are usually better at knowing how THC dosages affect them, making it easier to know if it's okay to drive.
By using similar testing methods that are administered to drunk drivers, cops can easily fail to catch impaired drivers or cut loose people who are so high that they might pass out behind the wheel. The AAA is using the study to recommend that states with legal weed use a different method to determine driver ability. It wants Colorado, Montana, Nevada, Ohio, Pennsylvania, Washington, and any other state that legalizes pot to use an observation-based system where a trained officer analyzes behavioral indicators to see if a driver is too stoned to drive. According to the numbers, marijuana increases the likelihood of a crash, but not nearly as much as cellphone use or drunk driving.