The decline was predicted earlier this year in a report put out by Governors Highway Safety Association, and it attributed the drop to the weather; 2012 was warmer than usual, leading to more people getting out on two wheels. The return of normal weather patterns in 2013 meant fewer riders, and that meant fewer deaths.
For the data we have so far, almost every metric saw a drop. Injuries declined to 88,000 compared to 93,000 in 2012, unhelmeted deaths were 1,854 versus 2,039 in 2012, and 27 percent of riders involved in fatal crashes had a Blood Alcohol Level of .08 or higher, as opposed to 28 percent in 2012. Breaking down that last number, however, the 21-24 and 55-64 age groups did go up by one percent, where all other age groups either declined or stayed the same. Just going by the black-and-white figures, the report delivers news that's less bad than before, but the two-wheeled game remains a dangerous one: the other three vehicle types tracked each account for less than one single death per 100 million vehicle miles traveled; in the same amount of miles traveled, 23.4 motorcyclists die.
You can peruse the numbers on the Quick Facts sheet, or in the full report.