Whenever the proposed path of a road or railway is obstructed by a hillside, a waterway or some form of construction, the engineer designing the project has to decide whether or not it is practical to construct a tunnel through or under the obstacle.

• 通常,拟建中的公路或铁路遇到山丘、河道或其他建筑物时,该工程的工程师就得决定能否开凿隧道从障碍物中或障碍物下穿过。