The London–Aylesbury line is a railway line between London Marylebone and Aylesbury. This line is operated by Chiltern Railways although half of the line is owned by London Underground (16 miles/26km). The total length of the route is 39 miles (63km) with 16 stations in total. Maximum speed is 75mph. The route currently sees 3 types of rolling stock, the class 165 and 168 for Chiltern Railway and the S Stock for the Metropolitan Line. As the Class 165 is already used on the Great Western Express Dovetail can easily remodel and rebrand the train. class 165 and 168 Although Chiltern Railways skip out a few intermediate stops it would be fun if we could also operate the Metropolitan line from Harrow on the Hill, either as a semi-fast service to Amersham or an all station service to Amersham calling at: North Harrow, Pinner, Northwood Hills, Northwood, and Moor Park. There could be options to include the Watford and Chesham Branches. The weekday off peak service goes as followed: 1. Marylebone - Aylesbury: 2tph with 1tph extended to Aylesbury Vale Parkway 2. Aldgate - Amersham: 2tph - All Stations from Harrow on the Hill 3. Aldgate - Chesham: 2 tph - All stations from Harrow on the Hill Both Met line services can see Semi-fast trains during the peak. This route would be ideal as it’s fairly short only reaching 39 miles. It would see a brand new terminus station added to the game (London Marylebone) and would see a new Underground line partially added without needed to develop a whole underground line.
You might as well include the Met line to Baker Street instead of stopping at Harrow, it still runs mostly parallel to the Chiltern line until terminating at Marylebone, where the Met line diverges into the tunnels at Baker Street. Also I don't think the Class 168 is permitted operating to Aylesbury via Amersham as they don't have the compatible safety systems fitted to allow running alongside tube stock. The Class 165 and 172? are however.
Strictly speaking the Turbo in GWE is a 166 so you would probably need to start from scratch for a 165. My ideal for this route would be a classic era pack giving Class 115 DMUs for the BR service, A60 stock on the Met and a guest appearance from Sarah Siddons on a railtour.
115s would be fantastic. If class 165 were to be done then it might be wise to do the /0 for Chiltern Railways and the /1 for GWE at the same time.