If there is going to be a 4 month blockade at Farnworth they will need to do something along the lines of either re-open the route for Metrolink via Bury, (Well, Radcilffe, theres only a few houses in the way and one might be able to loop round them) to take the strain from Bolton or put a coard / loop in around Hindley kind of area so that services can run North out of Bolton and on to Manchester via Atherton.
EDIT: Or to be less extreme, put in crossovers either side of the tunnels and run 3tph of a massive length as a shuttle 6x23/20m (Six car 150s running round), and divert everything else. As in 3tph from Preston to Victoria or Airport, send all other services via the Chat Moss or Atherton.
What do people think to trying to jam in 4tphpd through the big tunnel that won't need any major work doing to it, (then swapping sides to do the other one).
If we can do 3tph, I'd have all of these running Preston - Victoria or Preston - Oxford Road, one of these would stop at each intermediate station (Moses Gate, Farnworth, Kearsley) and journies between each of these replaced by buses. 2tph would run a shuttle between Wigan Wallgate / North Western and Bolton, terminating in Platform 4, Clitheroe would be curtailed to Bolton and run into Platform 1 and terminate. Alternativly be diverted via Lostock Hall and the Chat Moss for direct services, although that could prove un-nessesarry. 3tph would then run from Preston to Manchester via Bolton formed up as 6 car 150s (The longest the route through Salford can take and stop) or 6 car 185s (proberbly more popular with the locals) calling with a standardey pattern all the way. Possibly have one service start AT bolton in Platform 3.