The U.S. Department of Transportation has proposed a two-year phase-out or retrofit of DOT-111 rail tank cars. Retrofits would involve thicker shells, electronic braking and protections to prevent rollovers. It also aims to set a 40 mph speed limit for trains with older tank cars, and for urban areas with a population of more than 100,000. New or retrofitted cars could travel up to 50 mph outside of urban areas. Comments on the proposed rules will be accepted for 60 days.