It's long been the plan to open Crossrail in three phases, starting with the central section and eventually connecting everything up. That's not changed. But a big adjustment has been made to what the intermediate phase will look like, silently revealed in papers for an upcoming TfL meeting, because it turns out there's a better more efficient way to do it.
Here's how things are at present (and have been since the end of 2019). One arm out west from Paddington towards Heathrow and Reading, and one arm out east from Liverpool Street towards Shenfield.
Officially this is Stage 2 (following the 2015 takeover of the Shenfield line which was stage 1). Everything's currently branded TfL Rail because the Queen's name doesn't get a look-in until Crossrail properly connects.
What's coming next is Stage 3, the opening of the central section, a long-delayed event currently due "in the first half of 2022".
A full service will operate between Paddington and Abbey Wood with trains running every five minutes. But this won't yet be proper Crossrail because the two suburban arms won't connect up, terminating at Paddington and Liverpool Street mainline stations while the new services operate underground.
In terms of branding only the central section will launch as the Elizabeth line while the two separate outliers continue to operate as TfL Rail. And because the central section is entirely separate from the rest of the rail network it can open as soon as it's ready, without having to wait for the nod from National Rail.
Here's what was planned to happen next, that's Stages 4 and 5.
Stage 4 would have seen services from Shenfield connected to the central section, just west of Stratford, completing the rollout of Crossrail across east London. But the TfL Rail brand would have lingered on across west London, until eventually in Stage 5 the final tunnels opened and the disconnect at Paddington was removed.
That's now not happening.
Instead the powers-that-be have thought again and come up with a new optimised approach "which both reduces operational and performance risks and helps maximise the benefits to passengers as early as possible". It's clever, broadly beneficial and should deliver additional money via fares and branding.
The central section opens as expected next year, that's Stage 3. But the next stage (renumbered 5b) will see two simultaneous tweaks rather than just one. Services from Shenfield will operate to Paddington, as previously planned, but services to/from Reading/Heathrow will also be diverted to operate through the central section to Abbey Wood.
The cunning bit is that this creates "two separate but overlapping railways", one from Shenfield to Paddington and one from Abbey Wood through Paddington. The two can be operated entirely separately, interleaving with each other through the central section, bringing all the benefits of the final configuration (5c) but without the technical complexities.
It works because trains will either operate on the National Rail network in the west or on the National Rail network in the east, not both. It's efficient because drivers need only be trained on one set of National Rail procedures, not two. It's more resilient because the previous version had a huge number of trains reversing at Paddington and this plan halves that. And it's convenient because it'll utilise the existing Shenfield and Reading timetables, just extended into the tunnels, so doesn't need to wait for a specific National Rail timetable changeover date.
Financial bonus 1 is that passengers from the west will be whisked direct into the West End for the first time, which is expected to provide a welcome boost to TfL revenue. It also works the other way, for example with Canary Wharf now connected direct to Heathrow, and this all happens one stage earlier than it would have done before. Financial bonus 2 is that TfL will be able to ditch their TfL Rail branding at this point and go full-on purple, taking more money off advertisers and sponsors, potentially six months earlier than they could have done otherwise.
The final stage is still the same, seamless interconnectedness with trains from Shenfield finally allowed out to Reading and Heathrow. But this time the general public may not even notice, because under the revised scheme the benefits of catching purple trains straight across London will already be a thing.
No timings for the last two stages have been provided, just as we don't yet have a specific date for Paddington to Abbey Wood services to begin. But if Stage 3 takes place in the first half of 2022 then Stage 5b might well kick in at the end of 2022, with the final Stage 5c being introduced at the subsequent spring (or winter) timetable changeover day.
In which case this month's change to project phasing means the Crossrail service pattern during a substantial portion of 2023 will be as follows.
It won't look like this on the map, it'll only operate like this underneath, but the campaign to rename the two lines Elizabeth I and Elizabeth II starts here.