作废
BS 4521-4-1975 专用铁路道岔规范.第4部分:英国铁路机车不运行的、轴负荷可超过25吨的重型平底钢轨岔道Specification for railway turnouts for private users - Heavy grade turnouts over which British Railways locomotives do not operate, for axle loads which may exceed 25 tons, using flat bottom rails