That's an impossible number to calculate. Just today, in fair but flowing traffic, I noticed a vehicle braking constantly and erratically. The person behind t

That's an impossible number to calculate. Just today, in fair but flowing traffic, I noticed a vehicle braking constantly and erratically. The person behind them apparently had enough and swerved to my lane to pass them, nearly causing an accident that wouldn't have involved the other driver. Sure enough, it was a middle aged lady staring at her phone.