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Most jurisdictions that allow off-duty use of police vehicles cite substantial and worthwhile benefits. Cruisers parked in neighborhoods serve as a crime deterrent, and off-duty officers can respond quickly from home to nearby crime scenes. Other pluses include potentially lower maintenance costs and longer vehicle lives for permanently-assigned vehicles compared to those assigned to department motor pools. Finally, some studies show most residents like the idea and feel more secure.
I think that most of these arguments are biased in favor of the take-home policy. For example, some surveys suggest that approximately one-half of take-home police vehicles are unmarked. Whatever the percentage, these unmarked vehicles would have no crime deterrence effect. And, arguments about lower maintenance and longer vehicle life may fall apart when one considers that a take-home vehicle, by defintion, will have more "non-business" miles on its odometer per unit time (if the vehicle is used as intended, an additional round-trip commute more in miles per work day). The typical argument that makes take-home vehciles "seem" cheaper is the fact that a take-home car lasts about 5 years before it attains 90,000 miles of use (this is a common replacement mileage value) versus 1.8 years for a pool car. What this argument misses is the fact that the pool car has been used on average for 26,000 more on-duty patrol miles (assumes a 10 mile each way commute over five years) than the take-home car or at least 0.4 FTE more in on-duty patrol time than a take-home car. In addition, costs for auto liability insurance per mile driven are approximately $0.02 to $0.08 (depends on jursidiction). Assuming the average jurisdiction in terms of severity, the imputed additional auto liability insurance cost for a take-home vehicle is $260 per year. Using the 2009 IRS mileage rate, the value to officers with take-home vehicles is about $14,300 per year assuming 26,000 personal miles per year.