How could the cop see them doing 55 if the conditions were zero vis?

“Very low visibility — Visibility of less than 100 metres (330 ft) is usually reported as zero.” --https://en.wikipedia.org/wiki/Visibility

That's about how far high beams shine, so it's totally acceptable for cops to give people speeding tickets for doing 55 in a 55 at night with high beams on?

https://getjerry.com/questions/how-far-do-low-beams-shine

High beams definitely do not get 100 meters of usable distance in fog, and in fact will reduce the visibility further.

https://www.weather.gov/safety/fog-driving says:

“

    • Use fog lights if you have them.
    • Never use your high-beam lights. Using high beam lights causes
      glare, making it more difficult for you to see what’s ahead of
      you on the road.

”