So for example, if you were at Birmingham New Street and in the bottom link then you would get to go to Lichfield City and back five times in a shift, but if you were in the top link then you would have a nice run to Cambridge or Preston or somewhere. It's not exactly like that any more but the basic principle is the same. Link 1 covers a certain number of routes and type of traction, Link 2 different routes and traction, Link 3 different stuff again (and so on) and while there would be plenty of overlap between the links, eg the guys in Link 1 would sign the traction and some of the routes Link 3 get every day, there are several different groups of drivers working off of different rosters. It makes organising everything a lot less complicated at a big depot as you are basically breaking the work down into bite sized chunks.