I don’t think this it’s worth being reported for asking for a source on this kind of claim. I would argue of a middle ground though. I think field tests origins came from a good intent of trying to distinguish intoxicated drivers but has morphed over the years and used to give reason to search your belongings. I think the original post is wrong, the intent is not to arrest people but they are commonly used as a means to get cause to search your vehicle.

And I don’t have a source, so it’s anecdotal but one of those things where you read enough of these cases and even see how cops are trained that the intent for most stops unrelated to genuine traffic violations is to get cause to search the vehicle.

I think back to some of those corridors within the United States where law enforcement abuse cash forfeiture laws to take peoples money.

I recall that a lawyer who talked about how they were developed and explained how they work, came to that conclusion. The tests are completely subjective, and the way they are graded means that unless you are an Olympic-level athlete, you will fail it. Can you balance on one foot without swaying or puting the other foot down (even when you first start and find your balance), with your eyes closed, for one minute?

Might I suggest that you research it and post what you find.

Their obvious ineffectiveness for the stated purpose, combined with the effectiveness for the unstated, hidden purpose.

I don't know, like, common sense and your eyes?

Think of a field sobriety test. Now think of if that actually tests for sobriety. There, there's your source.