feasible and prudent alternative
An alternative that avoids or minimizes harm to historic sites and other protected areas under Section 4(f) or Section 106 and is feasible because the alternative could be built as a matter of sound engineering, and is prudent because it would not result in unique problems, truly unusual factors, or cost and community disruption of extraordinary magnitudes; must be adopted by the federal agency unless it can be shown to be not feasible and prudent. (Bucher, 1996)