Canton viaduct

The Maryland Transportation Authority plans to move ahead with a $178 million project to replace the heavily deteriorated Canton Viaduct, pictured beneath I-95. (Jed Kirschbaum, Baltimore Sun / August 8, 2011)

On the north end of the Baltimore Harbor Tunnel, where northbound drivers emerge from the dark and southbound motorists descend into it, stands one of the oldest and most decrepit parts of Maryland's toll-financed transportation network.

The bridge called the Canton Viaduct carries Interstate 895 for two-thirds of a mile over city streets and railroad tracks and ducks between the concrete pillars that support Interstate 95. The Maryland Transportation Authority has at least a half-dozen projects under way or soon to begin at the Harbor Tunnel, Fort McHenry Tunnel and Key Bridge. But none of the system preservation projects come close to the Canton Viaduct's price tag of $178 million.

Maryland Transportation Secretary Beverley Swaim-Staley, who chairs the authority, said the costs of maintaining an aging system — the newest parts of which date to the mid-1980s — are among the reasons the agency has proposed the largest series of toll increases in the state's history.

Those tolls have sparked outrage from motorists, who by 2013 would pay an additional $4 to make a round trip via any of the harbor crossings and an extra $5.50 at the Bay Bridge. The increases, which would bring each round trip to $8, have been defended by state officials, who say they need the money to maintain safety and usability of important thoroughfares and to pay off the bonds on new projects such as the $2.6 billion Intercounty Connector.

The Canton Viaduct is at the crossroads of that debate.

The 36,000 drivers who rumble across the pitted and cracked deck of the bridge each day can easily tell that the road needs work, but a visit to the viaduct's underside clearly shows why the bill for that project adds up. Looking up at the steelwork that supports the driving surface, an observer can see extensive rusting. The concrete pillars that hold the bridge aloft also are crumbling in places, exposing the steel rebar within.

The Canton Viaduct, built between 1955 and 1957 at a cost of $6.6 million in that era's dollars, is showing its age.

"If you go by life cycle, it's time," said Dan Williams, the authority's deputy director of engineering. "It's not going to get better on its own."

The board of the Maryland Transportation Authority, following a recommendation from its engineering staff, decided last month that the viaduct needs to be replaced in its entirety rather than rehabilitated. (Rehabilitation would cost $167 million — only $11 million less than the price of a full replacement, engineers told the board.)

Williams said the bridge is considered "structurally deficient." On the 10-point scale that the federal government uses to rate bridges, the Canton Viaduct gets scores ranging from 4 (poor) for its driving surface to 6 (satisfactory) for the concrete pillars that elevate the roadway. But Williams said the bridge is still safe for travel. If it weren't, authority officials say, they would close it down.

The cost of the new bridge would not be borne by Maryland's taxpayers. It would be paid for out of the tolls collected by the transportation authority at the Harbor Tunnel and at the state's seven other toll facilities.

The viaduct is part of the network that lets travelers cross Baltimore's harbor and avoid having to crawl through downtown or take a wide, looping route around the western Beltway. But it is hardly the only section of the network that's in need of repair. The other projects planned for the three Harbor crossings and their approaches collectively cost more than $150 million.

"It's not just new facilities," Swaim-Staley said. "It's also that we keep the things we have functional as well as safe."

But Swaim-Staley acknowledged that motorists might not make the connection between projects such as the Canton Viaduct and the tolls they pay.

"If they notice it's a bridge, they probably think it's part of the State Highway Administration — not part of the tunnel for which they've just paid the toll," she said.

The secretary said that several years ago her department and the authority conducted a comprehensive assessment of the Baltimore area's toll facilities and found that much of the system needed expensive maintenance work.

"The longer you wait, the more it's going to cost you," she said.

Williams said that's the case with the Canton Viaduct. Like a 20-year-old car, its maintenance costs grow with each passing year. At this point, he said, it's more cost-effective to replace the bridge from the ground up.

"We don't want to put a brand-new superstructure on a close to 60-year-old substructure," he said. The bridge is expected to be at least that old when the project is completed.