While smart phone adoption may have plateaued there may be continued increase in distracted driving. Smart phone adoption had the greatest increase between about 2010 and 2016 from 35-75% of US adults who say they own a smart phone, but the number of people who use their phones while driving may have continued to rise.
Especially as younger drivers are more comfortable with smart phone use over all, instant response and connection is expected, and apps have become more distracting.
Some additional items to look at might be non fatal accidents, are cyclists just as likely to be hit by cars, but more likely to die because of the increase in size of car, reduction in helmet use, or increased shared road speeds?