Motorcycle deaths jump nationwide but fall in California. Why?

Motorcycle fatalities on U.S. roads rose 10% in 2015, according to estimates from the Governors Highway Safety Assn.

Those estimates show that more than 5,000 motorcycle riders died in 2015, up from 4,548 in 2014. That makes 2015 the third year in history when the body count was above 5,000.

In...