How will over-the-limit, DUI driving infractions be determined [View all]

under the newly legalized pot laws in CO and WA?

Just had an interesting conversation with my brother who's an ER doc in CA. He sees the catastrophic results of alcohol/drug-related driving on a daily basis.

In CA, he sees road accidents due to THC impairment even under CA's legalized medical marijuana laws.

Question: How are pot smokers and law enforcement supposed to determine when someone is driving under the influence?

How can a smoker know if they're over some "impairment" limit? If they've toked one too many? Will there be some sort of roadside test similar to the breathalizer?

THC cannot be detected on the breath, apparently. So, will they have to come up with instant blood-drawing kits for use by the highway patrol?

Enquiring minds want to know...just how will this brave new world of legalized pot work out on the road?

P.S. I'm all in favor of legalization. Just wonder about what adjustments society will have to make. I don't think letting stoners drive willy-nilly after several joints would be a really safe bet.

At best, they'd tend to fall asleep at the wheel. At worst, their lack of alertness and slow reflexes would be a menace to themselves and others.

Edit: typos