For police, 2010 was a difficult year. After 2009, when the number of officers who died in the line of duty hit a 50-year low at 117, deaths in uniform jumped 37 percent last year, to 160. Fifty-nine of those killed were shot, up from 49 in 2009; 73 were traffic fatalities.

What has analysts scratching their heads is that the spike in police deaths occurred during a year when many types of crime, including murder and assault, were down, according to FBI statistics. (In a twist that’s almost humorous, academic criminologists point out that recessions often bring lower crime rates, partly because a backlog of goods in stores brings down the resale value of stolen items. In other words, the fencing business takes a hit along with legitimate businesses.)

But a few “cluster killings”—incidents in which more than one officer is killed during the same action—can exert a heavy influence on the statistics. Last June, for example, two policemen were killed in Tampa after stopping a car that had no visible plate and was carrying an ex-convict wanted for passing a bad check. Last year saw five incidents in which two police were killed at once.

And the National Law Enforcement Officers Memorial Fund attributes the 2010 spike to fewer, more fatigued police officers and an increase in the number of stressed, distracted drivers.

It’s a hard fact that 160 police deaths in one year is not a new occurrence. For five of the last 10 years, more than 160 police have been killed annually in the line of duty. To put the figure of 160 in perspective, during the gang wars and street riots of the 1970s, nearly 200 officers a year were killed on the job.

In all, there are about 800,000 law enforcement officers—federal, state and local—on active duty in the U.S. The average age of those who died last year was 41, and with an average of 12 years on the job, they were not rookies. Massachusetts lost three officers, two from the eastern part of the state and one, David Zolendziewski, from the Holyoke Police Department (after his cruiser skidded on ice and hit a tree). Texas lost 18 officers, more than any other state.

Policing is not one of the most dangerous jobs in the United States—delivering pizzas is considered less safe—but the U.S. is not one of the safest places to do it. In the 48 years between 1961 and 2009, an average of only 2.7 police a year were murdered in Canada (pop. 43 million). In the United Kingdom, which has roughly one-fifth the U.S. population, only 143 police died on the job in the entire decade between 2000 and 2010, 15 from criminal acts, most in road accidents.