After seven months of delays and tens of millions of dollars in cost overruns, there is finally some good news: Passengers could be boarding Metro Silver Line trains this summer.

The Metropolitan Washington Airports Authority and Metro announced Thursday that they have reached an agreement that will allow MWAA additional time to complete its work on the $5.6 billion rail line even after the project is turned over to the transit authority.

The agreement means there won’t be the speedy turnover many had hoped for, but it provides a clear outline for what needs to be done to get the new rail line running.

“It is a big step forward,” said Pat Nowakowski, executive director of the Silver Line project, who announced last week that he was resigning to take a job with another transportation agency.

Metro General Manager Richard Sarles said if the transit agency waited until MWAA completed all the necessary work before taking custody of the project, passenger service probably wouldn’t begin until late 2014. Service originally was slated to begin in December 2013.

There are a number of critical issues MWAA must address before Metro takes possession of the line, Sarles said.

“While there are still outstanding items for the Airports Authority and their contractor to resolve, today’s agreement allows us to move this project closer to opening day for our customers by allowing certain tasks to be completed after the project is in Metro’s control,” Sarles said. “We expect that the Airports Authority will complete the remaining items in a timely fashion, thereby allowing us to open the line this summer.”

Sarles said Metro is likely to take control of the Silver Line next month, followed by up to 90 days of testing and training before passenger service begins.

Although it may speed up the opening, the agreement could mean additional costs for phase one of the project, which is already $150 million over budget. While that is a relatively modest amount for a project of this size, it is concerning to fiscal watchdogs and users of the Dulles Toll Road —who are paying the bulk of the project’s $5.6 billion price tag.

“There is a certain unknown,” Nowakowski conceded. “We still feel we will be very close to contract budget, but it’s difficult to know.”

MWAA officials also announced Thursday that the project’s contractor, Dulles Transit Partners, led by construction giant Bechtel, had met all conditions under its contract with the airports authority for the project to be considered “substantially complete.” That declaration, which came at the end of a 15-day review period, set the stage for the agreement between Metro and MWAA.

“Substantial completion is an important milestone that signals major work is finished and that soon riders will travel on a 21st-century transit system,” said Larry Melton, Bechtel’s executive director for the project. “This achievement is remarkable given the complexity of building a rail line in a densely populated area where 700,000 cars travel each day.”

One elected official described the news as “heading into the homestretch.”

“After decades of planning, intense politics and finally construction, we are heading into the homestretch on the first phase of rail to Dulles. I look forward to a quick handoff of the project from MWAA to Metro so we can welcome riders to the Silver Line this summer,” Rep. Gerald E. Connolly (D-Va.) said.

But regional leaders emphasized that it was important to keep the pressure on both agencies.

“While I welcome today’s news of additional progress on bringing rail to Dulles, I strongly encourage MWAA and WMATA to maintain a sense of urgency so that we will see the Silver Line up and running before the end of summer, said Sen. Mark R. Warner (D-Va.), who has been critical of the many delays that have plagued the project. “I urge everyone involved to pull together to get the remaining punch-list issues resolved quickly so we can move forward to the crucial safety testing. Too many travelers and taxpayers have waited too long for these final steps not to be resolved as quickly and efficiently as possible.”

Thursday’s announcements cap a tumultuous period for the rail project, which has had myriad problems ranging from faulty computer systems to emergency speakers that did not meet fire codes.

The news of Nowakowski’s resignation last week coincided with an acknowledgment from MWAA officials that attempts to fix a key component of the rail line, which had delayed completion of the project for several months, had failed. And while contractors have found a work-around that will allow the rail line to open, it will cost nearly $2 million and take a year to complete a permanent fix.

To many, the ongoing saga illustrates the bumpy road the project—one of the largest of its kind under construction in the country — has traveled since rail to Dulles was first conceived in the late 1960s. Northern Virginia leaders see rail to Dulles International Airport as a way to boost economic development and relieve traffic congestion. The transit line is expected to help transform traffic-choked Tysons into an urban oasis of walkable communities with shopping, night life, city-style residences and jobs.

But paying for and building the rail link have proved to be a difficult slog.

The Silver Line is the first line to be added to the 38-year-old Metro system in more than two decades. But because it is the first one not being built by Metro, it has required a previously unheard of level of cooperation between an agency that runs two of the region’s airports and a toll road, and one that manages its rail and bus system.

The first phase of the rail line will have four stations in Tysons and one at Wiehle Avenue in Reston. Preliminary work on the second phase, which will have six stops, including one at Dulles Airport, has recently begun and is expected to be completed in 2018.

The state of Virginia, the federal government and Loudoun and Fairfax counties are all contributing to the project, but the bulk of its costs are being paid by users of the Dulles Toll Road.

“It’s always frustrating to have something near the goal line and not be able to quite get it over the goal line,” Sarles said Thursday.

But he added: “I’ve been through system start-ups before. There are things that come up. The important thing is that we get it right. The last thing I would like to do is start the system prematurely, and then have problems with opening day and deliver bad service to our customers.”

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