Old Lyme - Amtrak is considering replacing the century-old bridge that spans the Connecticut River between the town and Old Saybrook.

The Connecticut River Bridge, a 1,500-foot steel rolling lift span structure, is "nearing the end of its useful life," says Amtrak.

Amtrak recently completed a study that identified two replacement options for the bridge, but would still need to secure funding for the long-term project estimated at $400 million.

Either a new bascule or a vertical lift bridge would replace the current bridge, which began carrying trains over the river in 1907, according to Amtrak. Today, Amtrak and Shore Line East passenger cars, as well as P&W freight trains, traverse the bridge.

The time frame for construction of a new bridge could be 2018 to 2021.

The Connecticut River Bridge would be Amtrak's latest in a series of bridge replacement projects in the region. Amtrak replaced the Thames River Bridge between Groton and New London in 2008 and the Niantic River Bridge between Waterford and East Lyme last year.

In the environmental study of the Connecticut River Bridge replacement, Amtrak calls the Connecticut River Bridge replacement "the next major improvement to address the operational reliability of the Northeast Corridor drawbridges."

Amtrak says in the environmental assessment, completed last month with the Federal Railroad Administration, that replacing the bridge would improve both rail service and navigation on the river.

"At times, the operational reliability of the aging bridge results in cascading delays to rail and maritime traffic due to its failure to open and close properly," the study states.

A 2006 inspection of the bridge found certain features to be "particularly problematic," including its mechanical operating system and the bascule span's rolling tread plates, according to the study.

One of the two bridge replacement options could also entail widening the bridge's channel and increasing its vertical clearance. The bascule bridge, one option, would keep the current 150 feet width and 68 feet vertical clearance for ships. However, a vertical lift bridge, another option, could either retain the current width or widen the channel by 50 feet. The vertical lift bridge would also increase the vertical clearance by at least 22 feet.

Amtrak estimates the project will cost about $400 million, but there is no source of committed funding for construction at this point, said Craig Schulz, a senior communications officer for Amtrak. The 2018 to 2021 construction time frame is an estimate, since the actual time frame depends on identifying a funding source, he said.

Amtrak will also need to secure permits for the construction and may need to stop construction during specific periods due to migrating fish or other wildlife concerns, the study states.

The final design, which would include more detailed engineering data, would take about two years to complete, Schulz said.

Amtrak is seeking public comments on the environmental study, which details the bridge replacement's effects, from noise and vibration to its impact on natural resources, until the end of the month. The study is available at the Phoebe Griffin Noyes Library in Old Lyme and the Acton Library in Old Saybrook. It is also online at www.fra.dot.gov.

k.drelich@theday.com