Currently, this concerns the State of Ohio. But, I think it's going to spread.
I don't know if you've all seen this article. Simply put, it states that a police officer's "visual estimate" -- without SMD verification "can be" used to convict a driver of speeding.
In WA state, at least, an officer's "visual estimate" has always been considered "probable cause" for a traffic stop, but there are NO cases as to whether a visual estimate alone can be considered a "preponderance of evidence", resulting in a conviction. Yet, Ohio's burden of proof is "beyond a reasonable doubt".
Anyway, I'll let the article speak for itself.