Traffic across the bridge began a slow decline in the 1950s as industry shrank in New England and with it the need for the raw materials railroads excelled at transporting.
Traffic from the connecting New York, Ontario & Western ceased when that railroad shut down on March 30, 1957.
Another connection, the coal-, slate-, and cement-hauling Lehigh & New England, shut down in 1961.
At the same time, some new traffic began crossing the bridge, such as the New Haven's "Super Jet", one of the first trains to carry truck trailers.
The Penn Central's acquisition of the New Haven in 1969 discouraged connecting traffic with the Erie Lackawanna, which competed with other Penn Central routes.
After 1971, only one through train in each direction, for Erie Lackawanna, crossed the bridge.

While the Penn Central did not connect with the old New Haven on the west side of the bridge, it came close.
For a short time in 1969 and 1970, Penn Central ran a daily train between Cedar Hill Yard in New Haven, Connecticut and Potomac Yard in Alexandria, Virginia, by way of the Lehigh and Hudson River Railway, which connected with the Penn Central Belvidere Division in Belvidere, New Jersey, 72 miles south of the old interchange with the New Haven at Maybrook Yard in Maybrook, New York.
The service ended in a dispute over haulage charges and the traffic was diverted to the longer all-Penn Central route through Selkirk, New York.
Ironically, the only reason the Lehigh and Hudson River was not part of the Penn Central was because a Penn Central predecessor, the Pennsylvania Railroad, had prevented the New Haven from acquiring it in 1905.
The Lehigh and Hudson River and Erie Lackawanna were finally joined with the Penn Central when all were taken over by Conrail in 1976.

On May 8, 1974, a tie fire damaged about 700 feet (210 m) of decking and underlying girders on the bridge's eastern section.
It was likely started by a spark from an eastbound freight train that had just crossed the span.
The Penn Central had neglected the bridge's fire-protection system, which had no water on the day of the fire, and had laid off employees who kept watch for such fires.
A photograph of the last train, a run-through from the Erie Lackawanna, was included in a 40th anniversary web feature by the Poughkeepsie Journal.

In August 1974, the Penn Central applied for $1.75 million to repair and improve the bridge from the federal government through the Regional Rail Reorganization Act of 1973.
By 1975, efforts had shifted to acquiring a combination of state and railroad funding.
In November 1975, a formal agreement between the New York State Department of Transportation and the trustees of the Penn Central was approved, allowing the $359,000 insurance payout for the bridge to be spent on repairs, with the state paying the rest.
In December, U.S. Representative Benjamin A. Gilman announced that $486,000 appropriated by the state legislature for repairs was undergoing final review by the state.
Authorization for the state to spend its share on bridge repairs had still not been given when, on April 1, 1976, ownership of the bridge changed with the inception of Conrail.
Having been forced to include the route over the bridge (the Maybrook Line) in its new system at the behest of Connecticut Senator Abraham Ribicoff, Conrail announced that it would not promise to repair and use the bridge despite a Connecticut foundation's offer to pay half the repair cost if the bridge were used again.
The railroad further said that other work required to make the route usable would raise the reactivation cost to $45.8 million.

Seven years passed; pieces of the bridge's eastern approach viaduct over Poughkeepsie began falling onto U.S. Route 9 below, damaging passing vehicles.
In response, the city sued Conrail and forced it to spend $300,000 in 1983 to remove the decking over the superstructure.
Conrail then sought to dispose of the unused bridge and eventually abandoned and tore up the Maybrook Line between Hopewell Junction and Maybrook, New York in 1983–1984.
Traffic across the bridge began a slow decline in the 1950s as industry shrank in New England and with it the need for the raw materials railroads excelled at transporting. Traffic from the connecting New York, Ontario & Western ceased when that railroad shut down on March 30, 1957. Another connection, the coal-, slate-, and cement-hauling Lehigh & New England, shut down in 1961. At the same time, some new traffic began crossing the bridge, such as the New Haven's "Super Jet", one of the first trains to carry truck trailers. The Penn Central's acquisition of the New Haven in 1969 discouraged connecting traffic with the Erie Lackawanna, which competed with other Penn Central routes. After 1971, only one through train in each direction, for Erie Lackawanna, crossed the bridge.
While the Penn Central did not connect with the old New Haven on the west side of the bridge, it came close. For a short time in 1969 and 1970, Penn Central ran a daily train between Cedar Hill Yard in New Haven, Connecticut and Potomac Yard in Alexandria, Virginia, by way of the Lehigh and Hudson River Railway, which connected with the Penn Central Belvidere Division in Belvidere, New Jersey, 72 miles south of the old interchange with the New Haven at Maybrook Yard in Maybrook, New York. The service ended in a dispute over haulage charges and the traffic was diverted to the longer all-Penn Central route through Selkirk, New York. Ironically, the only reason the Lehigh and Hudson River was not part of the Penn Central was because a Penn Central predecessor, the Pennsylvania Railroad, had prevented the New Haven from acquiring it in 1905. The Lehigh and Hudson River and Erie Lackawanna were finally joined with the Penn Central when all were taken over by Conrail in 1976.
On May 8, 1974, a tie fire damaged about 700 feet (210 m) of decking and underlying girders on the bridge's eastern section. It was likely started by a spark from an eastbound freight train that had just crossed the span. The Penn Central had neglected the bridge's fire-protection system, which had no water on the day of the fire, and had laid off employees who kept watch for such fires. A photograph of the last train, a run-through from the Erie Lackawanna, was included in a 40th anniversary web feature by the Poughkeepsie Journal.
In August 1974, the Penn Central applied for $1.75 million to repair and improve the bridge from the federal government through the Regional Rail Reorganization Act of 1973. By 1975, efforts had shifted to acquiring a combination of state and railroad funding. In November 1975, a formal agreement between the New York State Department of Transportation and the trustees of the Penn Central was approved, allowing the $359,000 insurance payout for the bridge to be spent on repairs, with the state paying the rest. In December, U.S. Representative Benjamin A. Gilman announced that $486,000 appropriated by the state legislature for repairs was undergoing final review by the state. Authorization for the state to spend its share on bridge repairs had still not been given when, on April 1, 1976, ownership of the bridge changed with the inception of Conrail. Having been forced to include the route over the bridge (the Maybrook Line) in its new system at the behest of Connecticut Senator Abraham Ribicoff, Conrail announced that it would not promise to repair and use the bridge despite a Connecticut foundation's offer to pay half the repair cost if the bridge were used again. The railroad further said that other work required to make the route usable would raise the reactivation cost to $45.8 million.
Seven years passed; pieces of the bridge's eastern approach viaduct over Poughkeepsie began falling onto U.S. Route 9 below, damaging passing vehicles. In response, the city sued Conrail and forced it to spend $300,000 in 1983 to remove the decking over the superstructure. Conrail then sought to dispose of the unused bridge and eventually abandoned and tore up the Maybrook Line between Hopewell Junction and Maybrook, New York in 1983–1984.
Walkway over the Hudson