I had an acquaintance who was a county constable. He once told me, "Let me watch you drive down the road, any road, for 30 seconds and I will be able to find a valid reason to pull you over." He implied that some part of their training was focused on exactly that.
One data point, and a highly regional one at that, I know.
The law is not on the citizens' side and never has been. Driving over the limit (even the smallest increment) is technically illegal. Driving under can be considered suspicious and warrant further surveillance (or more likely incite road rage from other drivers) in which you will likely make a mistake. Nobody follows every traffic law perfectly and in all likelyhood cannot. Every cop I have ever known has admitted to this fact and there are even more examples of former(or current) law enforcement officers going on record saying the same thing.
"Y.T.’s mom pulls up the new memo, checks the time, and starts reading it. The estimated reading time is 15.62 minutes. Later, when Marietta does her end-of-day statistical roundup, sitting in her private office at 9:00pm, she will see the name of each employee and next to it, the amount of time spent reading this memo, and her reaction, based on the time spent, will go something like this:
Less than 10 min.: Time for an employee conference and possible attitude counseling.
10-14 min.: Keep an eye on this employee; may be developing slipshod attitude.
14-15.61 min.: Employee is an efficient worker, may sometimes miss important details.
16-18 min.: Employee is a methodical worker, may sometimes get hung up on minor details.
More than 18 min.: Check the security videotape, see just what this employee was up to (e.g., possible unauthorized restroom break).
Y.T.’s mom decides to spend between fourteen and fifteen minutes reading the memo. It’s better for younger workers to spend too long, to show that they’re careful, not cocky. It’s better for older workers to go a little fast, to show good management potential. She’s pushing forty. She scans through the memo, hitting the Page Down button at reasonably regular intervals, occasionally paging back up to pretend to reread some earlier section. The computer is going to notice all this. It approves of rereading. It’s a small thing, but over a decade or so this stuff really shows up on your work-habits summary."
There was a recent case in Illinois where the district attorneys' office decided to create their own private police force that wasn't covered by any of the laws normally reserved for law enforcement, so it could do whatever the fuck it wanted.
I remember one guy they hired to sit and pull people over all day on the highway who said the same thing "I can find something wrong with every single vehicle that passes by. I can literally pull anybody over that I want." IIRC he had things like a corner of a mudflap being broken off, or some trivial insanity like that. The big one in Illinois was having any air freshener hanging from your mirror.
Law enforcement has enormous discretion for probable cause and can give straight up contradictory reasons for different cases, it is what officers are taught to do (i.e. something like driving too fast, driving too slow, driving too rigidly at the speed limit). This allows individual bias to overwhelm any attempt at equal enforcement. It's pretty well documented in both The New Jim Crow and Usual Cruelty, the Supreme Court has made it difficult to gather data in the last couple decades.
Any given american citizen is certainly breaking, at minimum, dozens of laws even while asleep in their own bed. If they want to pick you up and they are diligent enough they certainly can. They might be laughed out of court, but they also might not be.
One data point, and a highly regional one at that, I know.