The Elizabeth line that never was: The Watford Junction extension from Old Oak Common

"When Old Oak Common station opens to Elizabeth line services in a few years time, it could have included an option to extend the Elizabeth line up towards Watford Junction. Old Oak Common is the HS2 super-hub station being built between Ealing Broadway and Paddington, and in addition to the six HS2 platforms below ground, will include eight platforms above ground for Elizabeth line and GWR services to call at. Most of the westbound Elizabeth line services that currently terminate at Paddington are expected to go on to Old Oak Common. So they can get out of the way and reverse back into London, three turnback sidings are being included next to the station."

"It was initially planned for two sidings, but this was later increased to three. That's because the Elizabeth line service will be running at 18 trains per hour once Old Oak Common Station opens, and a Freedom of Information request has confirmed that they now have the potential to increase to up to 24 trains per hour in future. So far, so normal."

"However, back in 2014, the Secretary of State for Transport, Patrick McLoughlin, commissioned a report to investigate whether the sidings could include a short link to the West Coast Main Line (WCML). The WCML runs into Euston station, and the thinking at the time was that, considering the disruption at Euston during its rebuilding, some services could be diverted over the new link between the WCML and the Great Western Main Line into Paddington instead. That would reduce pressure on Euston station."

Old Oak Common is the HS2 super-hub being built between Ealing Broadway and Paddington with six below-ground HS2 platforms and eight above-ground platforms for Elizabeth line and GWR services. Most westbound Elizabeth line trains that currently terminate at Paddington are expected to continue to Old Oak Common, prompting inclusion of three adjacent turnback sidings (increased from two) to handle reversing and higher frequencies. The Elizabeth line will run at 18 trains per hour on opening with potential to rise to 24 tph. A 2014 report examined a short link from those sidings to the West Coast Main Line to divert services into Paddington and reduce pressure on Euston during its rebuild. Euston opening timing assumptions have since changed.

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