Be careful when merging the Yorkshire Routes 1-8 together.  If you merge all the routes together, then when you use the merge route, TRS04/06 will slow right down (almost nearly crashes), even on a high spec PC.
 
That's what happened to me when I merged Yorkshire Routes parts 1-8 together.  It got that bad that I had to delete the merged route to stop TRS04/06 from going extremely slow.