Definition of "by-pass"

In The Bus We Loved (2005) Travis Elborough describes the New Road [now named Euston Road and Marylebone Road] as 'London's first by-pass ... a kind of perimeter fence, a here be yokels boundary line between the burgeoning town and the country'.

2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, pages 17–18