Not quite.
If they have not surveyed that street in awhile, they cannot use radar (or lidar) speed guns to write speeding citations
But they can issue tickets to anyone violating the Basic Speed Law (essentially, ~“too fast for prevailing conditions”~ ) or Reckless Driving (presumptive at 20+ mph over posted limit).
Any obvious instance of speeding that doesn’t require radar or laser can still be ticketed. If you’re doing 30 in a 15 zone, “Officer’s expert estimate” is sufficient. No radar needed.
Ummm, again, no.
If the 85th percentile is doing 18, then the limit could be set to 18 (or 20 or 25), and then radar-enforced at ANY speed over that limit.
Also, a recent engineering survey that justifies the limit on the grounds of safety will permit radar surveillance regardless of drivers’ actual speeds.
So here’s the thing: Most urban roadways are set to speeds somewhat lower than the maximum safe engineered speed. About 85% of motorists will reflexively stay within a reasonable safety envelope,
regardless of posted speed. (The faster 15% are generally idiots, and are therefore ignored in these calculations.)
So the limit must be set to the speed of the 85th percentile (or above) if you want to use radar/lidar to issue citations.
Otherwise, you could be running an illegal speed trap: Setting the limit below anything justifiable by engineering safety or reasonable driver behavior, and then raking in ticket revenue from motorists who are driving in a perfectly sane and responsible manner.
NB: Your local jurisdiction may vary, but these are the rules on Baxter Street. (-:
