In cut and fill construction it keeps the route straight and/or flat, where the comparative cost or practicality of alternate solutions (such as diversion) is prohibitive. Contrary to the general meaning of cutting, a cutting in construction is mechanically excavated or blasted out with carefully placed explosives. The cut may only be on one side of a slope, or directly through the middle or top of a hill. Generally, a cut is open at the top (otherwise it is a tunnel).