I did overtime studies of Anchorage police & fire years ago. I doubt much has changed since then.  The amount of overtime that APD/AFD officers received in the past could increase their total annual compensation by 30-40% on top of already generous pay scales. Then, overtime rules allow the most senior officers -  those earning the most because of longevity- to get "first crack" at it.  
So when you see police directing parking at events or other non-standard patrol duties, they are usually the most senior officers & are making a HUGE hourly overtime pay for that duty.  Senior officers tend to start seeking a lot of overtime in the 3 years before their 20-year retirement timeline-  because all the overtime they earn in their final 3 years of working  is added into the calculation of the size of their annual retirement income.  I have known APD/AFD people with retirement incomes larger than the incomes they received while working! has been true under Dem/Republican mayors both. Always.