process "mild" (between 0.16% and 0.29% carbon) steel, while the two approach viaducts were built of iron. It formed part of the most direct rail route between the industrial northeastern states and the midwestern and western states. Operation The bridge was the only fixed Hudson River crossing between Albany and New York City until the construction of the Bear Mountain (road) Bridge in 1924, and was advertised as a way to avoid New York City car floats and railroad passenger ferries. Ownership of the bridge passed through several railroads including the Central New England Railway (CNE), New York, New Haven & Hartford Railroad (NH), Penn Central (PC) and Conrail. A strengthening of the bridge was completed in 1907 to handle heavier freight trains by engineer Ralph Modjeski, of the famed bridge civil engineering firm Modjeski and Masters, who added a third line of trusses down the middle, a central girder, and interleaved columns. In 1917–18, the double tracks on the bridge were converted to gauntlet track operation to center the weight of heavier New Haven Railroad 2-10-2 steam locomotives. Even so, trains were restricted to 12 miles per hour. In 1959, the gauntlet tracks were replaced by a centered single track. During World War II, the bridge was a vital link for war freight traffic, guarded around the clock by United States Army soldiers. At its peak, nearly 3,500 train cars crossed over the Hudson on a daily basis. Decline 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,