Construction on the Silver Line extension from Wiehle-Reston to Ashburn is complete, according to the Metropolitan Washington Airports Authority, which is in charge of the project. The project is years behind its original estimated completion date of 2016.

Now that construction is “substantially complete,” as MWAA announced today, the contractor will go through a series of tests to demonstrate the project’s functionality. After that, the project can be handed over to Metro, which will test the line to make sure it is safe and ready for passengers.

Metro says it will do about 200 tests to make sure they are getting what they ordered and ensure tracks and the train yard are safe for train operation. After that, for about 90 days, Metro will take provisional control and begin training, simulations, and emergency drills. Then Metro’s board will vote to accept the project and set an opening date.

Metro has not set a date for opening yet and likely will wait until they’re sure the line is ready. But in the past, Metro officials have estimated it could take about six months of work after construction to get the line ready, hire staff, and finish last-minute items. The Washington Metrorail Safety Commission will also need to sign off on the extension before it opens to the public. Earlier this year, Metro estimated the new extension would open around February 2022 — the latest projection after a series of postponements.

The project has suffered a series of construction issues that took time to fix or mitigate, including problems with cracking concrete, unlevel tracks, and track plates that hold the rails down weren’t to specifications.

But once open, the new line is expected to significantly ease travel for Northern Virginia residents and travelers who use Dulles Airport.

The extension will add 11.5 miles of track from the Wiehle-Reston East Station to a terminus near Ashburn in Loudoun County. It adds six new stations: Reston Town Center, Herndon, Innovation Center, Dulles Airport, Loudoun Gateway, and Ashburn.

“In addition to providing new public transportation options, the Silver Line is a major catalyst for jobs and economic development in the National Capital region,” Jack Potter, president and CEO of the Airports Authority said in a statement.

The project was designed and built by Capital Rail Constructors with Kiewit and Clark Construction Group.

“This significant milestone is a testament to the hard work, dedication, and collaboration of the project team and stakeholders,” Keith Couch, project director at Capital Rail Constructors said. “It is the result of the significant contributions of almost 10,000 craftworkers – a large contingent from the Capital region – all coming together to deliver an impactful project that we can be proud of. It has been an extraordinary team effort.”

A separate construction project for a new train yard at Dulles is also nearing substantial completion but MWAA provided no timeline for that project, which will also need to open before Metro begins service.