The 250-mile long system covers an area that goes from densely urban to glorious countryside in just asinglefare, easily transporting passengers from Central London into Epping Forest or the Chiltern Hills.
According to various studies, including a 1994 report in the Journal of Family Issues, children raised in single-father homes as a whole fare as well as those in single-mother homes.
Opening the Labour-led debate, Ms Eagle said her party would introduce a "strict cap" on fare increases, and would consider simplifying fare structures and introducing a"single national definition" for peak times.