FMCSA and PHMSA amend the Federal Motor Carrier Safety Regulations (FMCSRs) and Hazardous Materials Regulations (HMRs), respectively, to prohibit a driver of a commercial motor vehicle or of a motor vehicle transporting certain hazardous materials or certain agents or toxins (hereafter collectively referenced as "regulated motor vehicle") from entering onto a highway-rail grade crossing unless there is sufficient space to drive completely through the grade crossing without stopping. This action is in response to section 112 of the Hazardous Materials Transportation Authorization Act of 1994, as amended by section 32509 of the Moving Ahead for Progress in the 21st Century Act (MAP-21). The intent of this rulemaking is to reduce highway-rail grade crossing crashes.