No Easy Way To Measure How Much Marijuana Impairs Drivers

A new study out Tuesday from the AAA Foundation for Traffic Safety finds that it is very hard to accurately measure through a blood test whether someone's driving is impaired because of marijuana.

Another AAA study found that the number of fatal crashes involving a driver who had recently used marijuana doubled in Washington state in the year after recreational marijuana was legalized there. Here & Now's Jeremy Hobson talks to Jake Nelson, the AAA director of traffic safety advocacy and research about both studies.