CA police patrol lifecycles
Contra Costa County Sheriff runs their patrol sedans to 80,000 miles which should play out to about 36-42 months in service- also taking advantage of the extended warranty
CA Highway Patrol (CHP) runs their patrol vehicles to 100,000 miles which probably works out to cycling them every 2.5 - 3 years. They purchase the extended warranty as well.
Whichever lifecycle is established, it is important to rotate low and high mileage patrol vehicles as well as possibly rotating out sergeant or supervisor vehicles to equalize annual mileage as much as possible. Even if this means pulling a light bar and making a slick top or vice versa.