DUI checkpoints in Los Angeles, now include a saliva test for drugs...

[tofuandbeer]

http://www.scpr.org/news/2013/12/27/41219/la-dui-checkpoints-will-expand-testing-of-drug-imp/

Wow. I'm not a pot smoker, but this sounds like something that can easily be abused on the side of the police as needed.
I'm 100% for keeping folks sober while driving, but this one seems like it may be pushing it.

[Major Nikon]

1. Looks like it's voluntary

Though I can't imagine the police routinely informing people of their right to refusal.

State law requires drivers suspected of driving under the influence to submit to a blood test but they have the right to refuse the swab. The oral test is voluntary, said deputy city attorney Michelle DeCasas.