Metro-North Railroad commuters know what to expect when the 118-year-old Walk Bridge in Norwalk fails to close after boats pass underneath -- long hours stuck on a train waiting for repairs.

A federal Northeast Corridor advisory commission says the Walk Bridge, and three other 100-year-old rail spans in Westport, Greenwich and between Stratford and Milford, are seriously deteriorated and in need of replacement.

"These aging infrastructure assets are unreliable, technologically obsolete and increasingly prone to failures that create delays for riders," the Northeast Corridor Infrastructure and Operations Advisory Commission said in its first capital plan.

Established by Congress to develop recommendations for the rail corridor between Washington, D.C., and Boston, the Northeast commission proposes spending billions of dollars over the next five years to replace bridges and improve the vital rail system.

All of the Connecticut bridges highlighted by the commission are beyond the definition of old. The Devon rail bridge, which spans the Housatonic River between Stratford and Milford, was completed in 1905 and is listed on the National Register of Historic Places.

"Bridges built in the 1800s are, by definition, safety concerns," said U.S. Sen. Chris Murphy, D-Conn, who, along with others, is calling on Congress to immediately allocate $555 million for rail safety projects.

"Many of these bridges can be labeled as structurally deficient," Murphy said. "I think we have to show commuters we're serious about putting money in safety upgrades. I worry accidents, in combination with Congressional inaction, is going to start chilling ridership."

James Cameron, founder of the Commuter Action Group, said the bridges are a disaster waiting to happen.

"It's not a matter of if those bridges will fail, but when," Cameron said. "So their replacement shouldn't be an issue for debate but funding immediately, if not a decade ago."

Victorian-era bridges

The four largest rail bridges in Fairfield County -- the Cos Cob Bridge in Greenwich, the Saugatuck River Bridge in Westport, the Norwalk Walk Bridge and the Devon Bridge over the Housatonic River -- are remnants of another time.

Only the Walk Bridge, built in 1896, is now scheduled for replacement, at a cost of $465 million.

The Cos Cob Bridge over the Mianus River was completed in 1904, and is the busiest moveable bridge on the New Haven Line, which last year carried nearly 40 million passengers.

Estimates to replace the structure range up to $800 million.

"This bridge faces serious challenges caused by aging components and deferred maintenance," the Northeast commission said in its report, noting there is no funding "available or programmed" for replacement over the next five years.

The commission said if $50 million was available now, Connecticut could begin designing a new bridge.

The Saugatuck River Bridge was completed in 1904 and carries a replacement price tag of $350 million.

"Age and deferred maintenance have caused deterioration affecting both its electrical and mechanical components," the commission noted.

Connecticut plans to spend $20 million over the next five years for interim repairs on the bridge until a replacement can be funded.

The commission said the Devon Bridge, also known as the Housatonic River Rail Bridge, suffers from "serious deterioration" and requires $850 million to $1 billion to replace.

"Connecticut has initiated work on short-term repairs, but the entire structure needs to be replaced," the Northeast commission said, noting the state has earmarked $45 million to design a replacement.

Connecticut owns the commuter rail infrastructure within the state, including bridges, and is responsible for maintenance and replacement.

The rail tracks are used by the Metro-North Railroad, for its commuter rail service, and Amtrak, for its regional service.

`New Deal' for transit

Devon Puglia, a spokesman for Gov. Dannel P. Malloy, said the governor is well aware of the need to replace the bridges and complete major upgrades on the Metro-North system, which is why the governor is pushing a $100 billion, 30-year plan for rail, highway and infrastructure improvements.

"For too long, Connecticut dramatically underinvested in transportation and failed to think long-term -- and it's been bad for business, it's inconvenienced residents and halted the growth of our state," Puglia said.

"That's why we're working to transform our infrastructure with a historic plan," he said.

The Northeast commission recommended a new regional partnership under which the federal government, the eight states within the Northeast Corridor, the various railroads -- including Amtrak and Metro-North -- and others work together to develop funding sources.

"Many critical assets date back to a period between the Civil War and the New Deal," the commission said in its report.

"As infrastructure deteriorates and service levels reach the NEC's practical capacity, we must choose between declining reliability and limited economic growth or building the next generation of the railroad," the commission noted.

Murphy acknowledged his proposed $555 million infusion is a "drop in the bucket,'' adding the Northeast Corridor repair backlog stands at $21.1 billion. To move funding through Congress, Murphy said supporters will have to overcome spending caps lawmakers put in place in 2011.

"The terrible tragedy in Philadelphia is only the most recent reminder of the tremendous backlog," Murphy said, referring to the Amtrak crash earlier this month which killed four passengers and injured over 200.

State Sen. Toni Boucher, R-Wilton and a ranking member on the General Assembly's Transportation Committee, said both political parties understand the need to make major investments in both rail and highway infrastructure.

"This is what we have been talking about for a long time," Boucher said. "This is the oldest corridor in the country. It's difficult territory. Other places are flat and it's easier to build. We are stuck with old roads and bridges."

Boucher said ultimately the federal government must step up.

"We need a national basis, a New Deal, for transportation and mass transit," she said.