In states where marijuana is legalized recreationally (Colorado, Washington, Oregon and Alaska), the state must regulate marijuana as they do alcohol. Similar to alcohol, marijuana can also have dangerous consequences behind the wheel.
Since identifying a stoned drive is much harder than identifying if a driver is drunk, police are having a hard time coming up with a set system for the matter.
Although there is a class for officers to become “drug recognition experts”, there still is nothing that can compare to a breathalyzer for alcohol. This puts more pressure on the officer’s intuition than hard facts, raising some questions to the ethics of the matter.
Tell tales of stoned drivers could be varying speeds, meaning that they may speed up fast but then slow down again. Slow speeds are often more common as well, whereas faster speeds may be an indication of a drunk driver.
Research is still underway to create a device similar to a breathalyzer that can instantaneously detect the amount of THC on the breath.