8. 请简述五线制提速道岔各线的作用？
["X1\u7ebf\uff1a\u5b9a\u53cd\u4f4d\u52a8\u4f5c\u3001\u8868\u793a\u5171\u7528\u7ebf\uff1bX2\u7ebf\uff1a\u53cd\u4f4d\u2192\u5b9a\u4f4d\u52a8\u4f5c\u53ca\u5b9a\u4f4d\u8868\u793a\u7ebf\uff1bX3\u7ebf\uff1a\u5b9a\u4f4d\u2192\u53cd\u4f4d\u52a8\u4f5c\u53ca\u53cd\u4f4d\u8868\u793a\u7ebf\uff1bX4\u7ebf\uff1a\u5b9a\u4f4d\u2192\u53cd\u4f4d\u52a8\u4f5c\u53ca\u5b9a\u4f4d\u8868\u793a\u7ebf\uff1bX5\u7ebf\uff1a\u53cd\u4f4d\u2192\u5b9a\u4f4d\u52a8\u4f5c\u53ca\u53cd\u4f4d\u8868\u793a\u7ebf\u3002"]