Concerns have been raised that the opening of Crossrail could be delayed by the impact of Omicron.
The London Assembly is also seeking assurances from Transport for London about its ability to find extra cash if the costs of opening the long-delayed line continue to rise.
Up to five mass evacuation simulation exercises are due to be held over coming weekends to test the safety procedures on the new trains and stations.
But the assembly fears the high number of infections due to Omicron – London’s rate is currently 943 cases per 100,000 – could present a threat to the “dress rehearsal” tests and wider “trial operations” phase, which involves running 12 empty trains an hour throughout the day to test reliability.
TfL has permission to spend an extra £1.1bn to get the line open but has only been able to secure £825m of loans.
Last week TfL commissioner Andy Byford admitted that it was about £150m over the £825m secured and may need to ask the Department for Transport for further help if spending could not be reined back.
In a letter to Crossrail chief executive Mark Wild on Wednesday, the assembly’s transport committee wrote: “We acknowledge that a further discussion between TfL and the DfT would be required if TfL were not able to complete Crossrail within the current budget.
“The committee would like to understand what plans are in place to secure further funding from the Government, if it is required, and what plans are in place if Government does not provide that required funding.”
Crossrail announced on Tuesday that it remained on track to open the central section of the line between Paddington and Abbey Wood by the revised deadline of the end of June.
The line, which has cost in excess of £20bn, was originally planned to open in December 2018.
Caroline Pidgeon, chair of the assembly’s transport committee, said: “We were pleased to hear in our November meeting that Crossrail is still confident of opening the central section in the first half of 2022.
“However, a number of issues have concerned us – particularly if and how the Omicron variant will affect the launch timetable. It may be difficult to predict at this stage but an assurance that we will be kept updated is required.
“All Londoners look forward to their first trip on an Elizabeth Line train and we all hope that this long overdue project will be up and running as planned, early next year.”
Mr Byford told the Standard on Wednesday that he was confident that final costs could be brought closer to £825m and insisted there was no threat of blowing the £1.1bn maximum allowed.
Crossrail said the mass tests would use volunteers from TfL, Crossrail, contractors and partner organisations.
A TfL spokesperson said: “We remain vigilant to any Covid-19 developments and are very mindful of protecting our staff and volunteers. Every attendee will be required to take a lateral flow test and face coverings will be required throughout exercises. Participants will not attend exercises if they feel unwell or have been instructed to isolate.
“The Elizabeth line is extremely complex, and the trial operations phase will continue until it is clear that the highest levels of safety and reliability are in place before the railway can open to customers.”