Two Bay State motorists deemed “immediate threats” to public safety after being involved in crashes that killed two kids — and a T bus driver caught playing chicken in her rig — are all back on the road because of lax registry rules, a Herald review found. The survey of terrible motorists comes weeks after another reckless driver had been cleared to get his license back when authorities say he tore through Chatham near an ice cream parlor, killing one and maiming others. The RMV revoked 1,409 licenses last year from drivers deemed immediate threats by police, but the agency...