The National Highway Traffic Safety Administration says the number of motorcyclists killed in traffic crashes declined by 6.4 percent from 2012 to 2013, and the number injured dropped 5.4 percent, the American Motorcyclist Association reports.

In 2013, 4,668 motorcyclist fatalities were reported, down 318 from the 4,986 in 2012. Similarly, 88,000 “occupants” were reported to have been injured in motorcycle crashes in 2013, down from 93,000 the year before.

The NHTSA also reported that motor vehicle crash fatalities overall decreased by 3.1 percent in 2013 and injuries declined 2.1 percent.

One factor in the lower incidence of motorcycle crash fatalities was an 8.3 percent decrease in the number of motorcycle crashes in which the rider was impaired by alcohol, the NHTSA reported.

The NHTSA report also noted that there were 190 fewer fatalities in 2013 among motorcyclists aged 50 to 69 years. That decline represented 60 percent of the total decrease in motorcyclist fatalities.

The Motorcycle Crash Causation Study is the first comprehensive examination since the 1981 Hurt Report on the factors contributing to motorcycle crashes in the United States.

When the project is completed in 2016, it will provide a large and unique data set derived from actual motorcycle crashes and riders with similar risk characteristics, with a focus on the unique circumstances that produce motorcycle crashes.