Following those events, Maryland Sens. Paul S. Sarbanes and Barbara A. Mikulski successfully urged Congress to appropriate funding to study Baltimore's rail system for vulnerabilities. That study, released in 2005, found the Baltimore and Potomac Tunnel should be a top priority for reconstruction or replacement.

In 2010, Congress voted to set aside $60 million in American Recovery and Reinvestment Act funds to conduct an engineering study and an environmental impact study in conjunction with Amtrak.

Amtrak eventually awarded a contract to Parsons Transportation Group, which began the engineering work Nov. 1, according to Rob Kulat, a Federal Railroad Administration spokesman.

Parsons has put out a request for proposals for subcontractors interested in conducting the environmental work, which will consider regulations and requirements under the National Environmental Policy Act, Kulat said. That contract should be awarded by December, with work beginning in January, he said.

Galloway said he is eager for the study to be completed, as it will largely shape the course Amtrak charts forward. But he has some idea of what engineers are looking at.

"The focus right now is on constructing two new single track tunnels on a new alignment that would provide a 70- or 80-mph operating speed versus the 30 mph we see today," he said.

One tunnel would be for southbound trains, one for northbound trains. Their design would eliminate the sharp curves that restrict speed today.

"The current tunnel forms almost like a backwards 'S,'" Galloway said. "The working name for this new tunnel is called the 'Great Circle Route,' because it forms a pretty uniform arc north and west of the current tunnel."

While such a path would cut straight through West Baltimore, Galloway said there is "not the expectation that there will be many impacts on residential properties at all" because the tunnels would be 80 to 90 feet below the surface.

Trains enter the current tunnel from the west in Sandtown-Winchester and it winds northeast under Upton and Bolton Hill to emerge underneath the North Avenue Bridge over Jones Falls.

The southern portal into the two new tunnels would be in an existing industrial area near Sandtown, and the northern portal would be in an existing railway area near the Jones Falls, he said. The tunneling would not be cut-and-cover, like much of the existing tunnel's construction was, but would be conducted using state-of-the-art "boring machines," he said.

With new tunnels in place, the existing tunnel — if engineers don't suggest it should be filled in — could be converted to a single track to carry larger trains or be used to increase capacity during peak travel periods or in times of maintenance or emergency, Galloway said.

All the plans, of course, are subject to change and depend on favorable engineering reviews, Galloway said.

But finally, after decades of indecision and a lack of political will to fund the project, things look promising for replacing the post-Civil War-era tunnel, he said.

Funding will be a challenge, but public-private partnerships will be on the table and the federal government has indicated a desire to see long-decaying transportation infrastructure upgraded, he said.

"The odds of investing and making a really good improvement and a new major asset to the state of Maryland and the city of Baltimore," Galloway said, "is much more likely than it was a decade ago."