The full length Skipton to Carlisle line. It then has 3 'sections' of the layout to allow for faster loading times when you want need a short section of the route
However, if the route was not created in TC3 (say 2006), you will find there are likely problems
As an example - one route I downloaded used Auran's built-in track (built in in 2006) - this isn't present in TC3 - so the track doesn't appear - almost all of the route!
You can copy items from 2006 to TC3, but part of the TC process (As I understand it - and this moves to 2009) is that older assets will be removed from the built-in assets. This is to reduce the number of errors with assets (see lots of other threads here - 2006 & later have been progressively stricter about format of the information).
It's probably best to think of TC3 as the one supplied route +assets to build other UK routes from scratch.
It is a problem as the previous two posters have said but if you intend to start from scratch (i.e. you don't have previous editions of Trainz) it isn't a big deal, as you can immerse yourself in the Settle and Carlisle..