Not eight, not 12, but ten-hour shifts are the best if police departments want to reduce their overtime expenses and improve their officers' quality of life, according to a recent study from the Police Foundation.

The Shift Length Experiment: What We Know About 8-, 10-, and 12-Hour Shifts in Policing examines the impact of working hours on officers' performance, health, safety, quality of life and overtime. Researchers used the Detroit and Arlington, Texas, police departments as case studies.

Since the recession hit, a growing number of police departments have moved to longer shifts (or compressed workweeks) to make up for smaller budgets and in some cases, smaller workforces.

But the Police Foundation's study found that 12-hour shifts are actually the worst for officer's job performance and not the best for reining in overtime costs. According to the study, officers who work for half a day, three days a week are sleepier and less alert on the job than those who work eight or ten hours at a time. The report also shows that police officers with ten-hour shifts work the least amount of overtime -- five times less than those who work eight-hours.

Cash-strapped law enforcement agencies have targeted overtime as a way to reduce overall costs in recent years - some with success, others not so much.

Just last week, the Minneapolis Police Department, which has its patrols working ten-hour shifts, announced that it paid out its lowest amount of overtime in a decade. According to the Star Tribune, the MPD spent $2.8 million on overtime in 2011 when it had set aside $5.3 million. The department may use some of the extra $2.5 million to rehire a dozen officers, Deputy Police Chief Scott Gerlicher told KSAX-TV. MPD investigations and support staff work eight-hour shifts but are given the option to work ten, the department's public information officer, William Palmer, told Governing.

But the 10-hour workday isn't a perfect solution for all departments. In Glendale, Ariz., officers work 10-hour days, yet the agency is already worried about exceeding its overtime budget just seven months into the fiscal year, reports the Arizona Republic. That's because some cases -- like the disappearance of a local toddler and the shooting of an officer -- required extra manpower and showcase the unpredictable nature of policing.