A lot of it would be normal attrition. They're only required to work 20 years for "full" retirement benefits (although their retirement pay goes up if they choose to stay longer). Management (Captains, etc.) isn't the one working wrecks and writing speeding tickets, turnpike or otherwise and they're the ones that would be more inclined to stay on. At 45 or 50, most that are still "working the beat" are also about ready to hang it up. Police work, military, firefighting - all jobs that are a young man's game. There may be 60 year old generals and chiefs but I don't WANT there to be 60 year firefighters crawling around in houses dragging hoses. And while there's no reason a 60 year old can't drive a patrol and write a ticket, how many are in shape to wrestle over a gun with a belligerent perp. And they never know if the next stop won't be "that one".