The local police pick various arteries in the city. The focus on one area for a short time constantly moving to other areas.
In 5 days they issued almost 700 tickets in a one mile section. They then abandoned enforcement on that particular section for months.
Speed limits can vary on a given section of road. Drivers easily misjudge the prudent speed limit as enforcement is always in the lowest area. The Motorcycles usually sit back from the road and at times are in pairs.
If a group of cars is doing all the same speed they will not necessarily go after the lead, largest or fastest car.