Amtrak has unveiled an ambitious plan, which would cost $6.5 billion or more, to revamp Washington, D.C.,’s Union Station, adding capacity to handle future passenger traffic, preserving the historic station’s distinctive architecture, and seeking to give a boost to the local economy.

The expansion and alterations to the 1907 station, designed by Daniel Burnham, would be literally topped off by 3 million square feet of new, privately financed office, residential, and other buildings, to be constructed over the existing rail yard.

Amtrak estimates that the plan, which officials outlined at a kickoff event at the station on July 25, will cost $6.5 billion to $7.5 billion over 15 to 20 years. The privately funded buildings would cost an additional $1.5 billion.

Except for the master plan itself and some other early work, the financing for the station portion of the massive program is not in place.

Amtrak President Joseph Boardman told reporters that the funding would come from a combination of sources, including the railroad company, federal and local governments, and the private sector.  He said, “Amtrak’s going to pay for a lot of it,” but provided no specifics.

Asked whether it was problematic to release the proposal without an accompanying financial plan, Boardman said, “You’ve got to have a vision to get anything done.” He added, “If you don’t have a vision or a plan of where you’re going, you’re not going to get anything funded.”

Amtrak’s consultant team of Parsons Brinckerhoff and HOK helped to develop the plan.

The four-phase plan would retain the 105-year-old station’s architecture but convert its rear, or north, area into a much more spacious, multi-level complex.

The plan also calls for expanding the facility to handle some 300,000 passengers a day, triple its current volume, and doubling the number of trains it can accommodate.

In addition, the plan would bring the station into compliance with Americans with Disabilities Act and life-safety emergency-egress standards.