Cellphones can track what we say and write, where we go, what we buy and what we search on the internet. But they still aren’t being used to track one of the biggest public health threats: crashes caused by drivers distracted by the phones. More than a decade after federal and state governments seized on the dangers that cellphone use while driving posed and began enacting laws to stop it, there remains no definitive database of the number of crashes or fatalities caused by cellphone distraction