Biggest Resignalling Scheme on the networks history will close the line between Cardiff Central and the valleys, and several stations including paddington and london will either be partially or completely shut for several days. Our Transport Correspondent has more. It is going to be the biggest rail upgrade ever taken on, and it all starts late tonight, hitting services across south wales, london and manchester. The lack of trains will make the roads busier. This was the m6 today. And it is a popular time to fly away for the holidays. Here is sta nsted. So why do they always pick christmas to close the railways . We have a huge programme of works that we have to deliver, as part of our Railway Upgrade programme, and some of that work just cant be done on a live railway. We have to shut the railway. And so christmas is the best time to do it, because its one of the quietest times of year. 2a,000 engineers will work on 200 sites across britain. Well, one of the biggerjobs they are doing