Completion of London’s already delayed Crossrail project has been delayed again, into 2020, while cost overruns have risen by another $510 million-$830 million. Project officials now estimate the budget at $23 billion.

Originally due to open last December, the cross-London tunneled railroad was originally budgeted at $18.9 billion in 2010. With civil construction largely done, signaling and train software developments are now “the two critical paths,” says Mark Wild, chief executive of Crossrail Ltd., which is jointly owned by Transport fir London and the Dept. for Transport.

Train trial runs will start “at the earliest opportunity” next year followed full scale testing, Wild adds. Fitting out work on the tunnels is due to end in January while the tunneled section under central London will be “substantially complete” by March, except for stations at Bond Street and Whitechapel.

Crossrail, to be known as the Elizabeth Line, will link networks on either side of the city with 21 km of new twin tunnels through the center. Sections of Line outside of the center stretch are already in operation.