alt Hacker News> 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.
They'll have an opportunity to prove that in court. I know that's not a great solution (because of the penalties involved in simply being accused of a crime, but that's a different issue) but, remember, they were pulled over for driving erratically and the, through conversation, the officer would gain further reason to ask them to do the test. The problem is the driving, everything after that is evidence gathering.
These days, so much of that will be recorded on video, from the dash cam to the body cam, it's usually cut and dry that the person accused is under the influence of something.
> people with atypical minds or bodies
This is a reasonable concern so I don't want to dismiss it but this isn't even close to the typical situation and, to emphasize, the reason for the stop is usually bad driving and the officer is looking for an explanation. Before a sobriety test is administered, there is already a cause for being pulled over. So people who can't pass a sobriety test because they have a physical or mental reason they can't only have that one piece of evidence against them removed.
I'm sure you can construct a hypothetical case where a person with a speech impairment, an inner ear deformaty and who's eyes shake when moving left and right gets arrested for DUI because they appear impaired but they weren't pulled over for those reasons.