At 250 miles long, the London Underground is the second longest metro system in the world, after Shanghai at 270 miles long. The total rail network in London is one of the largest in the world, only Tokyo with, Crossrail being the latest extension to London's rail map.
However in a small corner of Hertfordshire, just outside the Capital, lies Watford, gateway to the north of the country and on the edge of the Metropolitan Line. But after a long fifty year wait, the Croxley Rail link is finally getting built. At some 4 miles long, London's Underground network slowly increases in size again. Who knows, we may catch up with Shanghai yet. But this plan was twenty years in the making...