If "singing along" is a leading indicator of being in an accident, then amazon should absolutely not employ drivers that sing along. People get injured or killed in accidents, we dont need to observe them if we have sufficently strong signals that show risk (IE: driving at 100mph, driving while drunk, etc). What I don't understand is if you tell drivers "dont sing along" does that negate the predictive value of "singining along" as a signal for propensity to be involved in an accident.