资料来源 : Webster's Revised Unabridged Dictionary (1913)

Broad gauge \Broad" gauge`\ (Railroad)
   A wider distance between the rails than the ``standard''
   gauge of four feet eight inches and a half. See {Gauge}.

资料来源 : WordNet®

broad gauge
     n : a railroad track (or its width) broader than the standard
         56.5 inches