A new cost-effective phased option for Old Oak Common. See the Central Viaduct option post for more details on the problems of the site and for a more comprehensive, but expensive, option.
Phase 1 builds on the planned construction of the Crossrail link from Old Oak Common (main) to the West Coast Main Line. Phase 1 of the TfL element simply adds a new viaduct link from the West London Line to the middle two platforms of Old Oak Common (main). This allows Southern services (green) from East Croydon to Milton Keynes to travel via Old Oak in addition to the Crossrail services to Tring.
(Old Oak Common main station is due to have 8 platforms, 4 for Crossrail and 4 for the fast lines. This plan aims to send 4tph of Southern services via the central 2 of the 4 Crossrail platforms. Crossrail 24tph plus Southern 4tph can be handled on 4 platforms.)
Phase 2 builds on phase 1 by constructing a new viaduct across railway lands in the North West of the site. This allows Overground services from Clapham Junction to reach Willesden Junction (two new platforms, north of the Bakerloo ones). This phase allows the existing line in the East to be closed and sold for development:
Phase 3 builds on phase 2 by diverting Overground services from Richmond via the new North Western viaduct. This would be accompanied by a new station in that area to serve the ongoing developments. This phase allows even more existing lines to be closed and sold for development:
Obviously, the final phase does not integrate Richmond services directly with HS2, but it does link it with Crossrail (the Tring services). Linking Richmond into the main Old Oak station would require two more platforms to cope with demand, which is a big ask at this initial stage.
As a final note, all the phases are compatible with extensions to link Old Oak Common to North Acton (and beyond) and to open an Overground route to Brent Cross.
Section added 28th September 2014.
This option was triggered by the release of the Crossrail to WCML link plans. When you overlay that link and the option A viaduct over Wormwood Scrubs, you have two very similar pieces of infrastructure, just at different levels. The Shared Loop makes no changes to the Crossrail plan save the ability to access the Dudding Hill line in phases 2 and 3 (in reality, some form of grade separation may be needed there).
In terms of vertical alignment, the Shared Loop option involves a simple, low gradient descent from the WLL to the GWML/Crossrail level to use the OOC platforms. This naturally means that it is at the correct level to be able to access the Crossrail WCML link which ends up on a bridge over Victoria Road. From there, the later viaduct runs over the freight depot to Willesden, which probably requires a reconstruction of the Old Oak Common Lane bridge over the WCML (or a higher than originally intended viaduct). I would also note that with increasing land values, the freight depot area could be considered for sale, making that viaduct simper to build (looking forward 10 years).
Finally, a key part of both the Central Viaduct option and this Shared Loop option is the goal of maximising the land available for development. The existing rail lines make the site difficult to access and develop, and fewer rail lines can have a big impact.
This blog outlines an alternate approach to Old Oak Common - the Shared Loop option.