Crossrail has announced it is entering a "crucial" development phase as it doubles the number of test trains.


The process involves "simulating a timetabled service" on the railway by running eight trains through its central tunnels.


The project was initially due to be completed in December 2018 but has been delayed and is over budget.


It is not expected to open until the first half of 2022, when it will be known as the Elizabeth line.


The line will run from Reading and Heathrow in the west to Shenfield and Abbey Wood in the east, calling at a number of central London stations.

It will include two sections of track currently operating under the TfL Rail banner - Liverpool Street to Shenfield and Reading to Paddington - as well as newly-constructed sections.

Many of the new stations are now nearing completion and some, such as Custom House, have already been handed over to Transport for London.


Crossrail Ltd chief executive Mark Wild said: "This is an incredibly important milestone for Crossrail to reach and puts us firmly on the journey to unlocking trial running next year.


"We are doing everything possible to deliver the Elizabeth line as safely and as quickly as we can, and we know that Londoners are relying on the capacity and connectivity the Elizabeth line will bring.


"This milestone also marks the incorporation of our Romford control room colleagues into the testing process, another sign that we are moving ever closer to our final goal of an operational railway."


Crossrail Ltd described delivery of the scheme as being "in its complex final stages", with "good progress" made on completing infrastructure work.

Construction work was temporarily paused earlier this year at the start of the coronavirus pandemic but this has since resumed in a Covid-secure environment.


The project was given £825 million more Government funding earlier this month.


Its budget was set at £15.9 billion in 2007 but it is now expected to cost around £18 billion.

When fully operational, the line will have capacity to carry around half a million passengers a day.