if the idea is to suggest an alternative to HS2 then that needs to be an alternative that holds some water.
Indeed.
I've seen someone suggest that we just do the works at Euston so that we could then run 12 coach 80x's with 900 seats (i.e. adding 3 standard class coaches to the 9 coach 80x's on GWR & LNER). As that would double the capacity of trains.
There's many problems with this:
It doesn't double capacity, even compared with the shorter 390's, as double 469 is 938 and double 589 is 1178.
Therefore you'd need to run more trains, now once the extra services from the ICWC franchise and the open access operators are running then there's no spare capacity (or at least so little that it's not going to do much but at much greater risk of things go wrong)
To do so would result in a train ~50m longer than the longer 390's, now London is sorted but what about (picking a station at random, and definitely not the most expensive one to deal with) Birmingham New Street?
Even once you've fixed Birmingham New Street you then have all the other stations, now with Liverpool you could have 2x6 coach units which split with half serving Liverpool. However that would reduce capacity in the trains from 900 to 864 when paired or 432 when running on their own. That's at least an 8% reduction in capacity but could be up to 27% reduction:
11 coach 390 - 589
1/2 size HS2 train - 550
9 coach 390 - 469
6 coach 80x - 432
Even once you overcome the issue with the stations you are still left with where do you maintain them and store them overnight.
Then there's the issue of the number of coaches within the fleets, taking Manchester as an example:
- class 390's (9+9+11 coach units), 5 hour unit cycle, 3tph - 145 coaches (1,527 seats/hour)
- HS2 trains (3*16 coach units), 3 hour unit cycle, 3tph - 144 coaches (3,300 seats/hour)
- class 80x 3*12 coach units), 5 hour unit cycle, 3tph - 180 coaches (2,700 seats/hour)
- class 80x 3*12 coach units), 5 hour unit cycle, 3.5tph - 210 coaches (3,150 seats/hour)
That's an extra ~65 coaches to provide double the capacity to Manchester compared to either the current fleet or to nearly match the HS2 fleet.
Now at this point I should point out that there'll be a need for some retained WCML services to Manchester after HS2, so there could be a need for (say) 2*9 coach trains an hour which would add a further 90 coaches. However, even assuming that these are class 390's these would take the hourly seating capacity to ~4,240.
Chances are they would be more akin to a 444 and assuming 3*5 coach units running a total service provision of 2tph (i.e. 1*10 & 1*5) that's 75 coaches and a total of 4,200 seats.
That's 1/3 more seats per hour than the 80x's could provide with only 9 extra coaches being leased, stored, maintained, etc. It also frees up at least one path compared to the existing service patterns. As well as allowing 1/2 a train to be split from the 5 coach unit which is serving Manchester.
That could allow a service to run; Euston, Watford Junction, Milton Keynes, Rugby, Coventry, Nuneaton, Stafford, Crewe (split), stations to Liverpool/Manchester