The snaking tunnel beneath West Baltimore where an Amtrak engine derailed Monday, disrupting travel for thousands of evening commuters, has been a source of concern for decades.
The narrow, two-track Baltimore and Potomac Tunnel twists 1.4 miles under the city, slowing the scores of passenger and commuter trains that use it each day.
The tunnel is a key "choking point" for Amtrak, which owns it, as well as for MARC and freight carrier Norfolk Southern, said Drew Galloway, Amtrak's chief of Northeast Corridor infrastructure, planning and performance. With service demands growing on the line that connects Washington to Baltimore and on to Philadelphia, New York and Boston, Amtrak has begun planning to replace the 140-year-old arched masonry tunnel.
A federally funded engineering study began this month to review options for rebuilding or replacing the tunnel. Rail officials envision boring two new tunnels — one running each way — deep beneath Baltimore, below the city's other major transit project, the Red Line.
Each day, about 85 intercity Amtrak trains and 60 MARC commuter trains move through the tunnel, but growing demand has Amtrak planning to expand service eventually to 140 trains per day and MARC looking to increase the frequency of its trains, Galloway said.
"Both systems are growing, in some cases growing rapidly, so the increasing demand for more service will only add to the number of trains operating through there," he said.
Simon Taylor, the Maryland Transit Administration's deputy administrator for planning, engineering and statewide services, said "having a faster tunnel, a more reliable tunnel, will be a great benefit" to MARC riders because it will allow MARC trains to circulate between Baltimore and Washington more quickly, possibly allowing for more trips.
Sustained growth would be impossible using the current tunnel, Galloway said.
Like much of Baltimore's underground infrastructure, the tunnel is frequently the victim of damage from ruptured water mains, Galloway said. Built in 1873, it's also the victim of age.
Perhaps more important, though, are the limitations of its design.
Its sharp curves restrict trains to 30 mph, well below their average speed. Its size means it can't accommodate modern freight trains or two-tier commuter trains.
Trains using it in both directions further complicates maneuvers and increases the likelihood of problems. Monday's minor derailment caused no injuries and all passenger cars remained upright, but the line was closed for hours, delaying even the morning commute.
None of the problems are new, and significant work on replacing the tunnel has long been delayed because of economic considerations. Current estimates put the work somewhere around $1.5 billion.
Still, the new study means new hope that decades of talk will translate into action, Galloway said.
"What's the alternative?" he said. "Shutting down the Northeast Corridor?"
Such a replacement would "end up vastly increasing the reliability of the service, because you wouldn't have the constant risk of losing this tunnel that's 140 years old," said Mitch Warren, executive director of the federal Northeast Corridor Infrastructure and Operations Advisory Commission.
The corridor can't be underestimated in importance, he said. Rail usage along it has exploded, particularly with the introduction of high-speed Acela trains at the end of 2000.
According to the commission, about 75 percent of the travel market between Washington and New York City used rail in 2011, compared with 37 percent by 2001.
"It's critical to continued service between D.C. and Baltimore, D.C. and Philly, D.C. and New York, D.C. and Boston," Warren said.
Addressing the tunnel's shortcomings emerged as a legislative priority for Maryland officials in 2001, after a huge crash and fire in the Howard Street Tunnel and the terrorist attacks of Sept. 11 refocused attention on the nation's and the city's aging, yet critical, infrastructure.