Yeah, no one LIKEs mixing bikes and cars on roads, but little is given towards making them separate. There are 4 things on a street being balanced though, pedestrians, bikes, greenery, buses, and cars. The first 3 IMHO should be the priority for a street (the area people travel short distances between close destinations). Roads on the other hand should be limited to buses, cars, and greenery OR a bike highway limited to bikes and greenery.
Like you said, though, using police as the primary method to enforce these separations is a failure of design. It would be like if Lemmy required you edit the webpages code to comment instead of having comment boxes, and having some dedicated to just going around and checking the code to make sure you were only putting in good formatted text and hoping they could punish people enough to do encourage it.
You would either shut down the site from excessive enforcement or shut it down from unusable design.