The Metropolitan Washington Airports Authority is seeking an additional $250 million to pay for construction of the second phase of the Silver Line rail project, citing the project’s complexity, coronavirus-related restrictions, an increase in the cost of building materials and supply chain slowdowns as key factors for the cost increase.

The additional money will push the price tag for the second phase of the rail line, which was originally scheduled to open in 2018, to just over $3 billion. The original estimate was about $2.8 billion. The total cost for both phases of the rail line will be about $6 billion.

The budget increase is the latest obstacle for a rail project that has sustained years of cost overruns, problematic infrastructure and political finger-pointing. It comes months before the extension is expected to open, creating a rail connection between the nation’s capital and its wealthiest county as well as Dulles International Airport.

The request for more money must be approved by the MWAA’s board of directors at a meeting Wednesday. MWAA is overseeing construction of the rail line, which will become part of the region’s Metro system and will be managed and operated by the Washington Metropolitan Area Transit Authority.

The additional cost would be spread among the project’s funding sources, which include Fairfax and Loudoun counties, the MWAA and Dulles Toll Road users.

Under the proposed agreement, Dulles Toll Road users would pay the bulk of the increase, about $188 million, according to the airports authority. According to a staff report, the project’s budget increase would not affect toll rates, which already were set to rise next year. Fairfax County would pay an additional $40 million, Loudoun County an additional $12 million and the MWAA an additional $10 million. Fairfax and Loudoun counties created special tax districts to pay most of the cost of the rail project.

It wasn’t clear Tuesday when project officials became aware the project had exhausted the $551 million contingency fund that had been set aside to cover cost overruns. Last month, a presentation to the MWAA board indicated the project was still on budget.

“Cost increases on projects of this size are never enjoyable, but are also not unusual,” said Jeffrey C. McKay (D-At Large), chairman of the Fairfax County Board of Supervisors. “That said, we will fully analyze and scrutinize the reasons to be sure that this is the very last financial adjustment for this project and that Fairfax County is under no further obligations for any capital payments.”

Matt Rogers, a spokesman for Loudoun County Board of Supervisors Chairwoman Phyllis J. Randall (D-At-Large), said she had no comment Tuesday on the proposed budget increase.

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MWAA officials said they are requesting the additional money after concluding negotiations with contractors and with officials at Metro. The funding will include a pool of money that Metro can tap to cover additional expenses related to issues that arose during construction, including concerns about defective panels installed at five of the six new stations that will be part of the rail extension.

Metro officials confirmed Tuesday that the agency had reached an agreement with the MWAA on a trust account to cover future expenses but referred additional questions to the airports authority.

The MWAA declared the second phase of the rail project substantially complete late last year. Metro took control of the rail extension last month, a milestone that raised the possibility that passenger service could begin this fall. Once open, the rail line will extend service into Ashburn and include a stop at Dulles Airport.

The 11.4-mile extension will add six stations to the Metrorail system. The Silver Line’s first phase, with four stops in Tysons and one in Reston, opened in 2014.

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Because it appeared to be less challenging than the project’s first phase, which involved constructing a tunnel under Tysons and building large sections of track over the Capital Beltway, airports authority officials had hoped they would save money on the project’s second phase. Initial bids to build the rail line came in below the MWAA’s estimates.

Those hopes were quickly dashed, and contractors found themselves dealing with problems. For example, an early decision to comply with new requirements for storm-water management added to the project’s cost and caused a 13-month delay. Subsequent projects pushed the project’s opening date even later.

By comparison, the project’s first phase, built by Bechtel, was six months late and more than $220 million over budget.

Bechtel had hoped to win the contract to build the rail line’s second phase, but the MWAA turned to a different company: Capital Rail Constructors, a joint venture between Bethesda-based Clark Construction Group and Kiewit Infrastructure Group. Hensel Phelps was hired to build the rail yard that also was part of the project.

The companies were selected by the MWAA not only for their technical expertise, but also because they said they could build the rail-line extension and yard for less than their competitors.

The delays have proved costly for the MWAA, which paid contractors more than $8 million to continue to supervise the project until it was ready to be turned over to Metro.

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