Phase 2 of Metro's Silver Line in Northern Virginia is substantially delayed.

The second phase of the project -- which is designed to eventually run trains to and beyond Dulles International Airport -- may not open until late 2019 or even 2020. The official timetable for the delay is 13 months.

The reason is attributed to more than 150 design changes that mirror adjustments made late in Phase 1 of the project, said the Metropolitan Washington Airports Authority (MWAA), the group behind the Silver Line project.

"Many of these modifications parallel design changes made in the latter stages of Phase 1 and will enhance the safety and reliability of Phase 2," said an MWAA release Monday.

Phase 1, which includes five new stations, opened with service between West Falls Church and Wiehle-Reston East in July 2014.

"For consistency, many of these same safety and reliability modifications needed to be incorporated into Phase 2 of the project, which then impacted the schedule," Charles Stark, MWAA's executive director of the Silver Line project, said in the release.

Although Phase 1 of the Silver Line has been open for months, there's still some more work to be done there, as well as close-out costs -- and that means additional funds. MWAA also revealed Monday that Phase 1 will require an additional $76 million, or another about 2.6 percent of the original planned cost.

MWAA said the new amount still remains within the original federally approved Phase 1 budget.

Tolls from the Dulles Toll Road are helping to finance a large percentage of the rail project, but MWAA said today that toll rates will not be impacted by these changes.