The US rail safety regulator issued rules on Friday meant to prevent the kind of runaway fuel-train accident that devastated a Canadian town last month. Under the rules, rail cars carrying hazardous materials such as combustibles may not be left unattended on main tracks or adjacent tracks unless specifically authorised. Railroads must boost their safety procedures and record-keeping for trains that carry hazardous material and are braked, according to the rules from the Federal Railroad Administration.