Railroad cutoff

Nicholson Cutoff (which travels over the Nicholson Viaduct in this 1989 photo) replaced an old route whose right-of-way now carries U.S. Route 11, the roadway shown in the foreground.

A railroad (or railway) cutoff (or cut-off) is a new railroad line built to replace or supplement an existing route, typically one where the old line is deficient for some reason.