I worked with Law Enforcement for 10yrs of my(previous) life, and have the greatest respect for them. My son-in-law is a cop up north. As for quotas, there are some states and/or municipalities that have them, but I think a lot of it comes from what Stadry inferred. We had a Lt that took complaints from local residents about speeding in various areas, and encouraged the patrolling of those areas. If these patrolmen did not have any tickets in a period of time, it wouldn't show enforcement? On another note, dating back before my time, I knew that State Police were required to patrol the highways and interstate at night, especially in winter(before cellphones), to ensure folks did not get stranded and freeze. To prove that, some of them would jack up their cars and run them, to spin the odometer! Or...towards the end of their shift, scream up and down the highway for miles!
Good times! Cheers!