It doesnt run on the Great Western Mainline it only runs on these routes Class 142s have operated the following routes: Bishop Auckland to Saltburn Blackpool South to Colne Carlisle to Newcastle Carlisle to Lancaster, via Barrow-in-Furness Cleethorpes to Sheffield (Saturday only) Hexham to Middlesbrough Heysham Port to Lancaster Huddersfield to Manchester Victoria Huddersfield to Sheffield Huddersfield to Liverpool Lime Street Hull to York via Selby Hull to Doncaster Leeds to Huddersfield Leeds to Sheffield via Barnsley (stopping service) Leeds to Sheffield via Wakefield Westgate (stopping service) Leeds to York via Harrogate Lincoln Central to Sheffield Liverpool Lime Street to Manchester Oxford Road via Warrington Central Liverpool Lime Street to Manchester Victoria, Stalybridge and Huddersfield Liverpool Lime Street to Warrington Bank Quay Manchester Piccadilly to Marple, Rose Hill Marple, New Mills Central Manchester Piccadilly to Hazel Grove (the Buxton line (NB: No service up to Buxton due to steep gradients)) Manchester Piccadilly to Sheffield (the Hope Valley line) Manchester Piccadilly to Chester via Stockport and Knutsford Manchester Victoria to Kirkby and Southport Manchester Victoria to Leeds via Brighouse Manchester Victoria to Leeds via Halifax Manchester Victoria to Clitheroe via Bolton Manchester Victoria to Blackburn via Todmorden Manchester Victoria to Rochdale Manchester Victoria to York MetroCentre and Newcastle to Morpeth Middlesbrough to Whitby Preston to Ormskirk Sheffield to Scunthorpe Stockport to Stalybridge (NB: One train a week, towards Stalybridge only) Todmorden to Kirkby Wakefield to Selby via Huddersfield and Bradford Wrexham Central to Bidston (No longer used due to route now transferred to the Arriva Trains Wales franchise) York to Sheffield via Rotherham Central
Hey Tom, this train won't be added on it own as it does not run on the Great Western Mainline. You will need to hope that DTG add a route that the train runs on.
Why don't you put this request in the Loco Suggestions forum (https://forums.dovetailgames.com/forums/loco-suggestions-proposals.77/)? You need to provide more justificaton as well. Have a look at some of the other suggestions - some of them have really excellent justifications.
i would love it but first we would be best of getting a lime street add on perhaps as a base add on that could incorporate serveral sub add ons with further routes or perhaps if this sort of system is possible add in the merseyrail northen line and have a way to get from Ormskirk to preston as a separate line after completing a full northern line Liverpool to Ormskirk route but i doubt any of these would be implemented anytime soon there will be other ideas in the works first