Costs associated with building Crossrail are "likely to continue to climb", a watchdog has said.
The Commons Public Accounts Committee said commuters in the South East have been let down by the delay in opening the new rail line.
A report published by the MPs noted that funding for the programme has already increased by around £2.8 billion to £17.6 billion, and "the final cost still remains unknown".
Crossrail was due to be completed in December last year, but the railway may not open in full until 2022.
The project is being jointly funded by the Department for Transport and Transport for London.
It is being built by Crossrail Ltd, which is an arm's-length body owned by TfL. The PAC found that Crossrail Ltd has "so far failed to understand the complexity and risks involved in the programme".
It added that the DfT "still does not appear to have got a grip" on the problem of cost increases and delays on major rail projects, citing the modernisation of the Thameslink and Great Western routes as previous examples.
Crossrail is two years late and #2.8 billion over budget. Unfortunately, delay and being over-budget now appear to be par for the course for major rail projects. Crossrail Ltd has failed to understand the complexity and risks of Crossrail, to manage its main contractors, and to integrate different strands of the programme successfully. The Department for Transport is ultimately responsible for the use of taxpayers' money on Crossrail. It still does not appear to have got a grip of the problems. It has also failed to get a grip of Crossrail Ltd, continuing to pay its executives bonuses despite the programme going off track.