The busiest section of the Fast Lines is between Euston and Ledburn Junction, with something like 15 trains in peak direction in peak periods. The standard pattern of evening peak departures is something like (off memrory)
XX57 Lancaster (Pendolino, first stop Tamworth)
XX00 Manchester (Pendolino, first stop Stoke)
XX03 Birmingham (Pendolino, first stop Rugby)
XX07 Liverpool (Pendolino, first stop Stafford)
XX10 North Wales (Voyager, first stop Milton Keynes)
XX13 LNWR (first stop Milton Keynes
XX16 LNWR (first stop Leighton Buzzard)
XX20 Manchester (Pendolino, first stop Milton Keynes)
XX23 Birmingham (Pendolino, first stop Watford then Coventry)
XX30 Glasgow (Pendolino, first stop Warrington)
XX33 Blackpool or Liverpool (Voyager/Pendolino, first stop Rugby)
XX40 Manchester (Pendolino, first stop Crewe)
XX43 Scotland via Birmingham (Pendolino or Voyager, first stop Milton Keynes)
XX46 LNWR (first stop Milton Keynes then Rugby)
XX49 LNWR (first stop Leighton Buzzard)
The signalling in theory permits departures every 3 minutes, but this is not achievable in practice since:
No xx27 departure is possible as the xx20 needs to stop on the Fast Line at Watford, and by the time it departs again the xx30 has caught up.
Similaly, no xx54 is possibe since the xx46 calls at Milton Keynes and is caught up by the xx57 as a result.
Therefore the only "spare" path might be considered to he the xx36...which is prudent to keep as a performance reserve after all of the above (and if it did run it would have linited options with what could be done with it).
Note in particular that the sequence of trains is careful and well-optimised (random it is certainly not). Notice for example:
-The sequence of trains running non-stop for a long distance at 57,00,03 and 07
-Then followed by an xx10 and 13 calling Milton Keynes (after the fast trains have passed), then a 16 which leaves the Slow Lines at Ledburn (giving 'space' for the 10/13 to call without blocking a train straight behind it).
Another example is the 23 calling at Watford, which gives space for the 20 to call at Milton Keynes.
A work of art to squeeze as many trains as possible out of this railway.