alt Hacker News> They have breathalyzers and blood tests. Field sobriety tests are not there to help police arrest drunk drivers, they're there to help police arrest whomever they want to.
You're wrong about that. "Sobriety" isn't limited to alcohol. You'll notice that most laws against drunk driving are actually against being "intoxicated" or "impaired". Breathalyzers and blood tests are for gathering indisputable evidence.
Field sobriety tests are there to determine if you're motor skills are impaired. If an officer observers a person driving erratically and they can't walk a straight line or touch their own nose, they shouldn't be driving. You can be arrested for DUI [of sleeping pills].
The only time police would specify a DUI was for alcohol is if a breathalyzer or blood test showed that. Even if the officer says there was a beer can on the floor and they smelled like alcohol, they could be under the legal limit and be on any number of other substances so the DUI wouldn't specify alcohol.
> If an officer observers a person driving erratically and they can't walk a straight line or touch their own nose, they shouldn't be driving.
There are plenty of reasons that someone might not be able to demonstrate this to the subjective opinion of an officer and be completely unimpaired and competent at driving. e.g. people with atypical minds or bodies
Police generally ask people to do these tests when they have already made up their mind about someone being impaired. The only point of the test, practically, is generate standardized documentation. It is a dog and pony show.
Other countries that have serious anti-driving-impairment programs don't use these types of subjective tests -- they test people for using the substances directly.