A new study by AAA's finds that it鈥檚 not possible to set blood-test thresholds for marijuana.
The findings come after six states, including Ohio, established tests for drivers suspected of marijuana impairment.
AAA's says marijuana鈥檚 impairing chemical differs greatly from alcohol and needs to be treated as such.
"We can鈥檛 use the same policy approaches we use on alcohol for marijuana," Nelson said. "We have to find an alternative."
AAA suggests states switch to more comprehensive measures for determining sobriety. One of those suggestions includes the use of a system that tests for recent marijuana use combined with assessing driver behavior.