(4)Where arailway crosses anavigable water way,and it is impossible to lift the line high enough for vessels to pass underneath without interception,a bridge must be built which is capable of being opened in order to allow the river or canal traffic to pass.在铁路经过通航河道的地方,如果那时不可能做到把线路升高到使船只在下面不受阻碍地通过的话,就必须把桥梁修成开启式的,以便江河或运河里的船只通过。