短語詞組短語asphalt cemented ballast bed 瀝青道床integrated ballast bed 整體道床integral ballast bed 整體道床width of ballast bed 道床寬度ballast bed finisher 平整道碴機track on ballast bed 碎石道床軌道elastic integral ballast bed 彈性整體道床integrate ballast bed 整體道床 返回 ballast bed